[GitHub] [pulsar] mattisonchao commented on a diff in pull request #17611: [feat][broker][PIP-195] Implement delayed message index bucket snapshot (create/load) - part2

[GitBox <gi...@apache.org>]

mattisonchao commented on code in PR #17611:
URL: https://github.com/apache/pulsar/pull/17611#discussion_r991133064


##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/Bucket.java:
##########
@@ -0,0 +1,122 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static org.apache.pulsar.broker.delayed.BucketDelayedDeliveryTracker.DELAYED_BUCKET_KEY_PREFIX;
+import static org.apache.pulsar.broker.delayed.BucketDelayedDeliveryTracker.DELIMITER;
+import com.google.protobuf.ByteString;
+import java.util.BitSet;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.CompletableFuture;
+import lombok.AllArgsConstructor;
+import lombok.Data;
+import org.apache.commons.lang3.mutable.MutableLong;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+
+@Data
+@AllArgsConstructor
+public class Bucket {

Review Comment:
   Maybe we can create two classes, one is `ImmutableBucket` and another is `MutableBucket`?



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/BucketDelayedDeliveryTracker.java:
##########
@@ -0,0 +1,628 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static org.apache.bookkeeper.mledger.util.Futures.executeWithRetry;
+import com.google.common.collect.HashBasedTable;
+import com.google.common.collect.Range;
+import com.google.common.collect.RangeMap;
+import com.google.common.collect.Table;
+import com.google.common.collect.TreeRangeMap;
+import com.google.protobuf.ByteString;
+import io.netty.util.Timeout;
+import io.netty.util.Timer;
+import java.time.Clock;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.concurrent.CompletableFuture;
+import javax.annotation.concurrent.ThreadSafe;
+import lombok.SneakyThrows;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.bookkeeper.mledger.ManagedCursor;
+import org.apache.bookkeeper.mledger.ManagedLedgerException;
+import org.apache.bookkeeper.mledger.impl.PositionImpl;
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.lang.StringUtils;
+import org.apache.commons.lang3.mutable.MutableLong;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.DelayedIndex;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotMetadata;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegment;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+import org.apache.pulsar.broker.service.persistent.PersistentDispatcherMultipleConsumers;
+import org.apache.pulsar.common.util.FutureUtil;
+import org.apache.pulsar.common.util.collections.TripleLongPriorityQueue;
+
+@Slf4j
+@ThreadSafe
+public class BucketDelayedDeliveryTracker extends InMemoryDelayedDeliveryTracker {
+
+    public static final String DELAYED_BUCKET_KEY_PREFIX = "#pulsar.internal.delayed.bucket";

Review Comment:
   What do you think to make the `bucketKey` to be a class?
   ```java
   class BucketKey {
      private static final String DELAYED_BUCKET_KEY_PREFIX = "#pulsar.internal.delayed.bucket";
      private static final String DELIMITER = "_";
      private final long ledgerId;
   
      // provide some method to get the ledger id
   }
   ```



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/BucketDelayedDeliveryTracker.java:
##########
@@ -0,0 +1,628 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static org.apache.bookkeeper.mledger.util.Futures.executeWithRetry;
+import com.google.common.collect.HashBasedTable;
+import com.google.common.collect.Range;
+import com.google.common.collect.RangeMap;
+import com.google.common.collect.Table;
+import com.google.common.collect.TreeRangeMap;
+import com.google.protobuf.ByteString;
+import io.netty.util.Timeout;
+import io.netty.util.Timer;
+import java.time.Clock;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.concurrent.CompletableFuture;
+import javax.annotation.concurrent.ThreadSafe;
+import lombok.SneakyThrows;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.bookkeeper.mledger.ManagedCursor;
+import org.apache.bookkeeper.mledger.ManagedLedgerException;
+import org.apache.bookkeeper.mledger.impl.PositionImpl;
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.lang.StringUtils;
+import org.apache.commons.lang3.mutable.MutableLong;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.DelayedIndex;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotMetadata;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegment;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+import org.apache.pulsar.broker.service.persistent.PersistentDispatcherMultipleConsumers;
+import org.apache.pulsar.common.util.FutureUtil;
+import org.apache.pulsar.common.util.collections.TripleLongPriorityQueue;
+
+@Slf4j
+@ThreadSafe
+public class BucketDelayedDeliveryTracker extends InMemoryDelayedDeliveryTracker {
+
+    public static final String DELAYED_BUCKET_KEY_PREFIX = "#pulsar.internal.delayed.bucket";
+
+    public static final String DELIMITER = "_";
+
+    private final long minIndexCountPerBucket;
+
+    private final long timeStepPerBucketSnapshotSegment;
+
+    private final int maxNumBuckets;
+
+    private final ManagedCursor cursor;
+
+    public final BucketSnapshotStorage bucketSnapshotStorage;
+
+    private long numberDelayedMessages;
+
+    private final Bucket lastMutableBucket;
+
+    private final TripleLongPriorityQueue sharedBucketPriorityQueue;
+
+    private final RangeMap<Long, Bucket> immutableBuckets;
+
+    private final Table<Long, Long, Bucket> snapshotSegmentLastIndexTable;
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        this(dispatcher, timer, tickTimeMillis, Clock.systemUTC(), isDelayedDeliveryDeliverAtTimeStrict,
+                bucketSnapshotStorage, minIndexCountPerBucket, timeStepPerBucketSnapshotSegment, maxNumBuckets);
+    }
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis, Clock clock,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        super(dispatcher, timer, tickTimeMillis, clock, isDelayedDeliveryDeliverAtTimeStrict);
+        this.minIndexCountPerBucket = minIndexCountPerBucket;
+        this.timeStepPerBucketSnapshotSegment = timeStepPerBucketSnapshotSegment;
+        this.maxNumBuckets = maxNumBuckets;
+        this.cursor = dispatcher.getCursor();
+        this.sharedBucketPriorityQueue = new TripleLongPriorityQueue();
+        this.immutableBuckets = TreeRangeMap.create();
+        this.snapshotSegmentLastIndexTable = HashBasedTable.create();
+
+        this.bucketSnapshotStorage = bucketSnapshotStorage;
+
+        numberDelayedMessages = recoverBucketSnapshot();
+
+        this.lastMutableBucket = new Bucket(-1L, -1L, new HashMap<>());
+    }
+
+    @SneakyThrows
+    private long recoverBucketSnapshot() {
+        List<CompletableFuture<Void>> completableFutures = new ArrayList<>();

Review Comment:
   Can it be given an initial value to avoid expansion?



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/BucketDelayedDeliveryTracker.java:
##########
@@ -0,0 +1,628 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static org.apache.bookkeeper.mledger.util.Futures.executeWithRetry;
+import com.google.common.collect.HashBasedTable;
+import com.google.common.collect.Range;
+import com.google.common.collect.RangeMap;
+import com.google.common.collect.Table;
+import com.google.common.collect.TreeRangeMap;
+import com.google.protobuf.ByteString;
+import io.netty.util.Timeout;
+import io.netty.util.Timer;
+import java.time.Clock;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.concurrent.CompletableFuture;
+import javax.annotation.concurrent.ThreadSafe;
+import lombok.SneakyThrows;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.bookkeeper.mledger.ManagedCursor;
+import org.apache.bookkeeper.mledger.ManagedLedgerException;
+import org.apache.bookkeeper.mledger.impl.PositionImpl;
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.lang.StringUtils;
+import org.apache.commons.lang3.mutable.MutableLong;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.DelayedIndex;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotMetadata;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegment;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+import org.apache.pulsar.broker.service.persistent.PersistentDispatcherMultipleConsumers;
+import org.apache.pulsar.common.util.FutureUtil;
+import org.apache.pulsar.common.util.collections.TripleLongPriorityQueue;
+
+@Slf4j
+@ThreadSafe
+public class BucketDelayedDeliveryTracker extends InMemoryDelayedDeliveryTracker {
+
+    public static final String DELAYED_BUCKET_KEY_PREFIX = "#pulsar.internal.delayed.bucket";
+
+    public static final String DELIMITER = "_";
+
+    private final long minIndexCountPerBucket;
+
+    private final long timeStepPerBucketSnapshotSegment;
+
+    private final int maxNumBuckets;
+
+    private final ManagedCursor cursor;
+
+    public final BucketSnapshotStorage bucketSnapshotStorage;
+
+    private long numberDelayedMessages;
+
+    private final Bucket lastMutableBucket;
+
+    private final TripleLongPriorityQueue sharedBucketPriorityQueue;
+
+    private final RangeMap<Long, Bucket> immutableBuckets;
+
+    private final Table<Long, Long, Bucket> snapshotSegmentLastIndexTable;
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        this(dispatcher, timer, tickTimeMillis, Clock.systemUTC(), isDelayedDeliveryDeliverAtTimeStrict,
+                bucketSnapshotStorage, minIndexCountPerBucket, timeStepPerBucketSnapshotSegment, maxNumBuckets);
+    }
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis, Clock clock,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        super(dispatcher, timer, tickTimeMillis, clock, isDelayedDeliveryDeliverAtTimeStrict);
+        this.minIndexCountPerBucket = minIndexCountPerBucket;
+        this.timeStepPerBucketSnapshotSegment = timeStepPerBucketSnapshotSegment;
+        this.maxNumBuckets = maxNumBuckets;
+        this.cursor = dispatcher.getCursor();
+        this.sharedBucketPriorityQueue = new TripleLongPriorityQueue();
+        this.immutableBuckets = TreeRangeMap.create();
+        this.snapshotSegmentLastIndexTable = HashBasedTable.create();
+
+        this.bucketSnapshotStorage = bucketSnapshotStorage;
+
+        numberDelayedMessages = recoverBucketSnapshot();
+
+        this.lastMutableBucket = new Bucket(-1L, -1L, new HashMap<>());
+    }
+
+    @SneakyThrows
+    private long recoverBucketSnapshot() {
+        List<CompletableFuture<Void>> completableFutures = new ArrayList<>();
+        this.cursor.getCursorProperties().keySet().forEach(key -> {
+            if (key.startsWith(DELAYED_BUCKET_KEY_PREFIX)) {
+                String[] keys = key.split(DELIMITER);
+                checkArgument(keys.length == 3);
+                Bucket bucket = createImmutableBucket(Long.parseLong(keys[1]), Long.parseLong(keys[2]));
+                completableFutures.add(asyncLoadNextBucketSnapshotEntry(bucket, true));
+            }
+        });
+
+        if (completableFutures.isEmpty()) {
+            return 0;
+        }
+
+        FutureUtil.waitForAll(completableFutures).get();
+
+        MutableLong numberDelayedMessages = new MutableLong(0);
+        immutableBuckets.asMapOfRanges().values().forEach(bucket -> {
+            numberDelayedMessages.add(bucket.numberBucketDelayedMessages);
+        });
+
+        log.info("[{}] Recover delayed message index bucket snapshot finish, buckets: {}, numberDelayedMessages: {}",
+                dispatcher.getName(), immutableBuckets.asMapOfRanges().size(), numberDelayedMessages.getValue());
+
+        return numberDelayedMessages.getValue();
+    }
+
+    private void moveScheduledMessageToSharedQueue(long cutoffTime) {
+        TripleLongPriorityQueue priorityQueue = getPriorityQueue();
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (timestamp > cutoffTime) {
+                break;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+            sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+
+            priorityQueue.pop();
+        }
+    }
+
+    @Override
+    public void run(Timeout timeout) throws Exception {
+        synchronized (this) {
+            moveScheduledMessageToSharedQueue(getCutoffTime());
+        }
+        super.run(timeout);
+    }
+
+    private Optional<Bucket> findBucket(long ledgerId) {
+        if (immutableBuckets.asMapOfRanges().isEmpty()) {
+            return Optional.empty();
+        }
+
+        Range<Long> span = immutableBuckets.span();
+        if (!span.contains(ledgerId)) {
+            return Optional.empty();
+        }
+        return Optional.ofNullable(immutableBuckets.get(ledgerId));
+    }
+
+    private Long getBucketIdByBucketKey(String bucketKey) {
+        String bucketIdStr = cursor.getCursorProperties().get(bucketKey);
+        if (StringUtils.isBlank(bucketIdStr)) {
+            return null;

Review Comment:
   I'm not sure if it is good to return null. because it has a risk to involve NPE.



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/BucketDelayedDeliveryTracker.java:
##########
@@ -0,0 +1,628 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static org.apache.bookkeeper.mledger.util.Futures.executeWithRetry;
+import com.google.common.collect.HashBasedTable;
+import com.google.common.collect.Range;
+import com.google.common.collect.RangeMap;
+import com.google.common.collect.Table;
+import com.google.common.collect.TreeRangeMap;
+import com.google.protobuf.ByteString;
+import io.netty.util.Timeout;
+import io.netty.util.Timer;
+import java.time.Clock;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.concurrent.CompletableFuture;
+import javax.annotation.concurrent.ThreadSafe;
+import lombok.SneakyThrows;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.bookkeeper.mledger.ManagedCursor;
+import org.apache.bookkeeper.mledger.ManagedLedgerException;
+import org.apache.bookkeeper.mledger.impl.PositionImpl;
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.lang.StringUtils;
+import org.apache.commons.lang3.mutable.MutableLong;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.DelayedIndex;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotMetadata;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegment;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+import org.apache.pulsar.broker.service.persistent.PersistentDispatcherMultipleConsumers;
+import org.apache.pulsar.common.util.FutureUtil;
+import org.apache.pulsar.common.util.collections.TripleLongPriorityQueue;
+
+@Slf4j
+@ThreadSafe
+public class BucketDelayedDeliveryTracker extends InMemoryDelayedDeliveryTracker {
+
+    public static final String DELAYED_BUCKET_KEY_PREFIX = "#pulsar.internal.delayed.bucket";
+
+    public static final String DELIMITER = "_";
+
+    private final long minIndexCountPerBucket;
+
+    private final long timeStepPerBucketSnapshotSegment;
+
+    private final int maxNumBuckets;
+
+    private final ManagedCursor cursor;
+
+    public final BucketSnapshotStorage bucketSnapshotStorage;
+
+    private long numberDelayedMessages;
+
+    private final Bucket lastMutableBucket;
+
+    private final TripleLongPriorityQueue sharedBucketPriorityQueue;
+
+    private final RangeMap<Long, Bucket> immutableBuckets;
+
+    private final Table<Long, Long, Bucket> snapshotSegmentLastIndexTable;
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        this(dispatcher, timer, tickTimeMillis, Clock.systemUTC(), isDelayedDeliveryDeliverAtTimeStrict,
+                bucketSnapshotStorage, minIndexCountPerBucket, timeStepPerBucketSnapshotSegment, maxNumBuckets);
+    }
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis, Clock clock,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        super(dispatcher, timer, tickTimeMillis, clock, isDelayedDeliveryDeliverAtTimeStrict);
+        this.minIndexCountPerBucket = minIndexCountPerBucket;
+        this.timeStepPerBucketSnapshotSegment = timeStepPerBucketSnapshotSegment;
+        this.maxNumBuckets = maxNumBuckets;
+        this.cursor = dispatcher.getCursor();
+        this.sharedBucketPriorityQueue = new TripleLongPriorityQueue();
+        this.immutableBuckets = TreeRangeMap.create();
+        this.snapshotSegmentLastIndexTable = HashBasedTable.create();
+
+        this.bucketSnapshotStorage = bucketSnapshotStorage;
+
+        numberDelayedMessages = recoverBucketSnapshot();
+
+        this.lastMutableBucket = new Bucket(-1L, -1L, new HashMap<>());
+    }
+
+    @SneakyThrows
+    private long recoverBucketSnapshot() {
+        List<CompletableFuture<Void>> completableFutures = new ArrayList<>();
+        this.cursor.getCursorProperties().keySet().forEach(key -> {
+            if (key.startsWith(DELAYED_BUCKET_KEY_PREFIX)) {
+                String[] keys = key.split(DELIMITER);
+                checkArgument(keys.length == 3);
+                Bucket bucket = createImmutableBucket(Long.parseLong(keys[1]), Long.parseLong(keys[2]));
+                completableFutures.add(asyncLoadNextBucketSnapshotEntry(bucket, true));
+            }
+        });
+
+        if (completableFutures.isEmpty()) {
+            return 0;
+        }
+
+        FutureUtil.waitForAll(completableFutures).get();
+
+        MutableLong numberDelayedMessages = new MutableLong(0);
+        immutableBuckets.asMapOfRanges().values().forEach(bucket -> {
+            numberDelayedMessages.add(bucket.numberBucketDelayedMessages);
+        });
+
+        log.info("[{}] Recover delayed message index bucket snapshot finish, buckets: {}, numberDelayedMessages: {}",
+                dispatcher.getName(), immutableBuckets.asMapOfRanges().size(), numberDelayedMessages.getValue());
+
+        return numberDelayedMessages.getValue();
+    }
+
+    private void moveScheduledMessageToSharedQueue(long cutoffTime) {
+        TripleLongPriorityQueue priorityQueue = getPriorityQueue();
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (timestamp > cutoffTime) {
+                break;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+            sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+
+            priorityQueue.pop();
+        }
+    }
+
+    @Override
+    public void run(Timeout timeout) throws Exception {
+        synchronized (this) {
+            moveScheduledMessageToSharedQueue(getCutoffTime());
+        }
+        super.run(timeout);
+    }
+
+    private Optional<Bucket> findBucket(long ledgerId) {
+        if (immutableBuckets.asMapOfRanges().isEmpty()) {
+            return Optional.empty();
+        }
+
+        Range<Long> span = immutableBuckets.span();
+        if (!span.contains(ledgerId)) {
+            return Optional.empty();
+        }
+        return Optional.ofNullable(immutableBuckets.get(ledgerId));
+    }
+
+    private Long getBucketIdByBucketKey(String bucketKey) {
+        String bucketIdStr = cursor.getCursorProperties().get(bucketKey);
+        if (StringUtils.isBlank(bucketIdStr)) {
+            return null;
+        }
+        return Long.valueOf(bucketIdStr);
+    }
+
+    private Bucket createImmutableBucket(long startLedgerId, long endLedgerId) {
+        Bucket newBucket = new Bucket(startLedgerId, endLedgerId, new HashMap<>());
+        immutableBuckets.put(Range.closed(startLedgerId, endLedgerId), newBucket);
+        return newBucket;
+    }
+
+    private CompletableFuture<Long> asyncSaveBucketSnapshot(
+            final String bucketKey, SnapshotMetadata snapshotMetadata,
+            List<SnapshotSegment> bucketSnapshotSegments) {
+        Long bucketId = getBucketIdByBucketKey(bucketKey);
+        checkArgument(bucketId == null);
+
+        return bucketSnapshotStorage.createBucketSnapshot(snapshotMetadata, bucketSnapshotSegments)
+                .thenCompose(newBucketId -> putBucketKeyId(bucketKey, newBucketId));
+    }
+
+    private CompletableFuture<Long> putBucketKeyId(String bucketKey, Long bucketId) {
+        Objects.requireNonNull(bucketId);
+        return executeWithRetry(() -> cursor.putCursorProperty(bucketKey, String.valueOf(bucketId)),
+                ManagedLedgerException.BadVersionException.class).thenApply(__ -> bucketId);
+    }
+
+    private CompletableFuture<Long> asyncCreateBucketSnapshot() {
+        TripleLongPriorityQueue priorityQueue = super.getPriorityQueue();
+        if (priorityQueue.isEmpty()) {
+            return CompletableFuture.completedFuture(null);
+        }
+        long numMessages = 0;
+
+        final long startLedgerId = lastMutableBucket.startLedgerId;
+        final long endLedgerId = lastMutableBucket.endLedgerId;
+
+        List<SnapshotSegment> bucketSnapshotSegments = new ArrayList<>();
+        List<SnapshotSegmentMetadata> segmentMetadataList = new ArrayList<>();
+        Map<Long, BitSet> bitMap = new HashMap<>();
+        SnapshotSegment.Builder snapshotSegmentBuilder = SnapshotSegment.newBuilder();
+        SnapshotSegmentMetadata.Builder segmentMetadataBuilder = SnapshotSegmentMetadata.newBuilder();
+
+        long currentTimestampUpperLimit = 0;
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (currentTimestampUpperLimit == 0) {
+                currentTimestampUpperLimit = timestamp + timeStepPerBucketSnapshotSegment - 1;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+
+            checkArgument(ledgerId >= startLedgerId && ledgerId <= endLedgerId);
+
+            // Move first segment of bucket snapshot to sharedBucketPriorityQueue
+            if (segmentMetadataList.size() == 0) {
+                sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+            }
+
+            priorityQueue.pop();
+            numMessages++;
+
+            DelayedIndex delayedIndex = DelayedIndex.newBuilder()
+                    .setTimestamp(timestamp)
+                    .setLedgerId(ledgerId)
+                    .setEntryId(entryId).build();
+
+            if (entryId <= Integer.MAX_VALUE) {
+                bitMap.compute(ledgerId, (k, v) -> new BitSet()).set((int) entryId);
+            }
+
+            snapshotSegmentBuilder.addIndexes(delayedIndex);
+
+            if (priorityQueue.isEmpty() || priorityQueue.peekN1() > currentTimestampUpperLimit) {
+                segmentMetadataBuilder.setMaxScheduleTimestamp(timestamp);
+                currentTimestampUpperLimit = 0;
+
+                Iterator<Map.Entry<Long, BitSet>> iterator = bitMap.entrySet().iterator();
+                while (iterator.hasNext()) {
+                    Map.Entry<Long, BitSet> entry = iterator.next();
+                    ByteString byteString = ByteString.copyFrom(entry.getValue().toByteArray());
+                    segmentMetadataBuilder.putDelayedIndexBitMap(entry.getKey(), byteString);
+                    iterator.remove();
+                }
+
+                segmentMetadataList.add(segmentMetadataBuilder.build());
+                segmentMetadataBuilder.clear();
+
+                bucketSnapshotSegments.add(snapshotSegmentBuilder.build());
+                snapshotSegmentBuilder.clear();
+            }
+        }
+
+        SnapshotMetadata bucketSnapshotMetadata = SnapshotMetadata.newBuilder()
+                .addAllMetadataList(segmentMetadataList)
+                .build();
+
+        final int lastSegmentEntryId = segmentMetadataList.size();
+
+        Bucket bucket = this.createImmutableBucket(startLedgerId, endLedgerId);
+        bucket.setCurrentSegmentEntryId(1);
+        bucket.setNumberBucketDelayedMessages(numMessages);
+        bucket.setLastSegmentEntryId(lastSegmentEntryId);
+
+        // Add the first snapshot segment last message to snapshotSegmentLastMessageTable
+        checkArgument(!bucketSnapshotSegments.isEmpty());
+        SnapshotSegment snapshotSegment = bucketSnapshotSegments.get(0);
+        DelayedIndex delayedIndex = snapshotSegment.getIndexes(snapshotSegment.getIndexesCount() - 1);
+        snapshotSegmentLastIndexTable.put(delayedIndex.getLedgerId(), delayedIndex.getEntryId(), bucket);
+
+        if (log.isDebugEnabled()) {
+            log.debug("[{}] Create bucket snapshot, bucket: {}", dispatcher.getName(), bucket);
+        }
+
+        String bucketKey = bucket.bucketKey();
+        CompletableFuture<Long> future = asyncSaveBucketSnapshot(bucketKey,
+                bucketSnapshotMetadata, bucketSnapshotSegments);
+        bucket.setSnapshotCreateFuture(future);
+        future.whenComplete((__, ex) -> {
+            if (ex == null) {
+                bucket.setSnapshotCreateFuture(null);
+            } else {
+                //TODO Record create snapshot failed
+                log.error("Failed to create snapshot: ", ex);
+            }
+        });
+
+        return future;
+    }
+
+
+    @SneakyThrows

Review Comment:
   Why `@SneakyThrows`?



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/BucketDelayedDeliveryTracker.java:
##########
@@ -0,0 +1,628 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static org.apache.bookkeeper.mledger.util.Futures.executeWithRetry;
+import com.google.common.collect.HashBasedTable;
+import com.google.common.collect.Range;
+import com.google.common.collect.RangeMap;
+import com.google.common.collect.Table;
+import com.google.common.collect.TreeRangeMap;
+import com.google.protobuf.ByteString;
+import io.netty.util.Timeout;
+import io.netty.util.Timer;
+import java.time.Clock;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.concurrent.CompletableFuture;
+import javax.annotation.concurrent.ThreadSafe;
+import lombok.SneakyThrows;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.bookkeeper.mledger.ManagedCursor;
+import org.apache.bookkeeper.mledger.ManagedLedgerException;
+import org.apache.bookkeeper.mledger.impl.PositionImpl;
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.lang.StringUtils;
+import org.apache.commons.lang3.mutable.MutableLong;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.DelayedIndex;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotMetadata;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegment;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+import org.apache.pulsar.broker.service.persistent.PersistentDispatcherMultipleConsumers;
+import org.apache.pulsar.common.util.FutureUtil;
+import org.apache.pulsar.common.util.collections.TripleLongPriorityQueue;
+
+@Slf4j
+@ThreadSafe
+public class BucketDelayedDeliveryTracker extends InMemoryDelayedDeliveryTracker {
+
+    public static final String DELAYED_BUCKET_KEY_PREFIX = "#pulsar.internal.delayed.bucket";
+
+    public static final String DELIMITER = "_";
+
+    private final long minIndexCountPerBucket;
+
+    private final long timeStepPerBucketSnapshotSegment;
+
+    private final int maxNumBuckets;
+
+    private final ManagedCursor cursor;
+
+    public final BucketSnapshotStorage bucketSnapshotStorage;
+
+    private long numberDelayedMessages;
+
+    private final Bucket lastMutableBucket;
+
+    private final TripleLongPriorityQueue sharedBucketPriorityQueue;
+
+    private final RangeMap<Long, Bucket> immutableBuckets;
+
+    private final Table<Long, Long, Bucket> snapshotSegmentLastIndexTable;
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        this(dispatcher, timer, tickTimeMillis, Clock.systemUTC(), isDelayedDeliveryDeliverAtTimeStrict,
+                bucketSnapshotStorage, minIndexCountPerBucket, timeStepPerBucketSnapshotSegment, maxNumBuckets);
+    }
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis, Clock clock,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        super(dispatcher, timer, tickTimeMillis, clock, isDelayedDeliveryDeliverAtTimeStrict);
+        this.minIndexCountPerBucket = minIndexCountPerBucket;
+        this.timeStepPerBucketSnapshotSegment = timeStepPerBucketSnapshotSegment;
+        this.maxNumBuckets = maxNumBuckets;
+        this.cursor = dispatcher.getCursor();
+        this.sharedBucketPriorityQueue = new TripleLongPriorityQueue();
+        this.immutableBuckets = TreeRangeMap.create();
+        this.snapshotSegmentLastIndexTable = HashBasedTable.create();
+
+        this.bucketSnapshotStorage = bucketSnapshotStorage;
+
+        numberDelayedMessages = recoverBucketSnapshot();
+
+        this.lastMutableBucket = new Bucket(-1L, -1L, new HashMap<>());
+    }
+
+    @SneakyThrows
+    private long recoverBucketSnapshot() {
+        List<CompletableFuture<Void>> completableFutures = new ArrayList<>();
+        this.cursor.getCursorProperties().keySet().forEach(key -> {
+            if (key.startsWith(DELAYED_BUCKET_KEY_PREFIX)) {
+                String[] keys = key.split(DELIMITER);
+                checkArgument(keys.length == 3);
+                Bucket bucket = createImmutableBucket(Long.parseLong(keys[1]), Long.parseLong(keys[2]));
+                completableFutures.add(asyncLoadNextBucketSnapshotEntry(bucket, true));
+            }
+        });
+
+        if (completableFutures.isEmpty()) {
+            return 0;
+        }
+
+        FutureUtil.waitForAll(completableFutures).get();
+
+        MutableLong numberDelayedMessages = new MutableLong(0);
+        immutableBuckets.asMapOfRanges().values().forEach(bucket -> {
+            numberDelayedMessages.add(bucket.numberBucketDelayedMessages);
+        });
+
+        log.info("[{}] Recover delayed message index bucket snapshot finish, buckets: {}, numberDelayedMessages: {}",
+                dispatcher.getName(), immutableBuckets.asMapOfRanges().size(), numberDelayedMessages.getValue());
+
+        return numberDelayedMessages.getValue();
+    }
+
+    private void moveScheduledMessageToSharedQueue(long cutoffTime) {
+        TripleLongPriorityQueue priorityQueue = getPriorityQueue();
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (timestamp > cutoffTime) {
+                break;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+            sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+
+            priorityQueue.pop();
+        }
+    }
+
+    @Override
+    public void run(Timeout timeout) throws Exception {
+        synchronized (this) {
+            moveScheduledMessageToSharedQueue(getCutoffTime());
+        }
+        super.run(timeout);
+    }
+
+    private Optional<Bucket> findBucket(long ledgerId) {
+        if (immutableBuckets.asMapOfRanges().isEmpty()) {
+            return Optional.empty();
+        }
+
+        Range<Long> span = immutableBuckets.span();
+        if (!span.contains(ledgerId)) {
+            return Optional.empty();
+        }
+        return Optional.ofNullable(immutableBuckets.get(ledgerId));
+    }
+
+    private Long getBucketIdByBucketKey(String bucketKey) {
+        String bucketIdStr = cursor.getCursorProperties().get(bucketKey);
+        if (StringUtils.isBlank(bucketIdStr)) {
+            return null;
+        }
+        return Long.valueOf(bucketIdStr);
+    }
+
+    private Bucket createImmutableBucket(long startLedgerId, long endLedgerId) {
+        Bucket newBucket = new Bucket(startLedgerId, endLedgerId, new HashMap<>());
+        immutableBuckets.put(Range.closed(startLedgerId, endLedgerId), newBucket);
+        return newBucket;
+    }
+
+    private CompletableFuture<Long> asyncSaveBucketSnapshot(
+            final String bucketKey, SnapshotMetadata snapshotMetadata,
+            List<SnapshotSegment> bucketSnapshotSegments) {
+        Long bucketId = getBucketIdByBucketKey(bucketKey);
+        checkArgument(bucketId == null);
+
+        return bucketSnapshotStorage.createBucketSnapshot(snapshotMetadata, bucketSnapshotSegments)
+                .thenCompose(newBucketId -> putBucketKeyId(bucketKey, newBucketId));
+    }
+
+    private CompletableFuture<Long> putBucketKeyId(String bucketKey, Long bucketId) {
+        Objects.requireNonNull(bucketId);
+        return executeWithRetry(() -> cursor.putCursorProperty(bucketKey, String.valueOf(bucketId)),
+                ManagedLedgerException.BadVersionException.class).thenApply(__ -> bucketId);
+    }
+
+    private CompletableFuture<Long> asyncCreateBucketSnapshot() {
+        TripleLongPriorityQueue priorityQueue = super.getPriorityQueue();
+        if (priorityQueue.isEmpty()) {
+            return CompletableFuture.completedFuture(null);
+        }
+        long numMessages = 0;
+
+        final long startLedgerId = lastMutableBucket.startLedgerId;
+        final long endLedgerId = lastMutableBucket.endLedgerId;
+
+        List<SnapshotSegment> bucketSnapshotSegments = new ArrayList<>();
+        List<SnapshotSegmentMetadata> segmentMetadataList = new ArrayList<>();
+        Map<Long, BitSet> bitMap = new HashMap<>();
+        SnapshotSegment.Builder snapshotSegmentBuilder = SnapshotSegment.newBuilder();
+        SnapshotSegmentMetadata.Builder segmentMetadataBuilder = SnapshotSegmentMetadata.newBuilder();
+
+        long currentTimestampUpperLimit = 0;
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (currentTimestampUpperLimit == 0) {
+                currentTimestampUpperLimit = timestamp + timeStepPerBucketSnapshotSegment - 1;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+
+            checkArgument(ledgerId >= startLedgerId && ledgerId <= endLedgerId);
+
+            // Move first segment of bucket snapshot to sharedBucketPriorityQueue
+            if (segmentMetadataList.size() == 0) {
+                sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+            }
+
+            priorityQueue.pop();
+            numMessages++;
+
+            DelayedIndex delayedIndex = DelayedIndex.newBuilder()
+                    .setTimestamp(timestamp)
+                    .setLedgerId(ledgerId)
+                    .setEntryId(entryId).build();
+
+            if (entryId <= Integer.MAX_VALUE) {
+                bitMap.compute(ledgerId, (k, v) -> new BitSet()).set((int) entryId);
+            }
+
+            snapshotSegmentBuilder.addIndexes(delayedIndex);
+
+            if (priorityQueue.isEmpty() || priorityQueue.peekN1() > currentTimestampUpperLimit) {
+                segmentMetadataBuilder.setMaxScheduleTimestamp(timestamp);
+                currentTimestampUpperLimit = 0;
+
+                Iterator<Map.Entry<Long, BitSet>> iterator = bitMap.entrySet().iterator();
+                while (iterator.hasNext()) {
+                    Map.Entry<Long, BitSet> entry = iterator.next();
+                    ByteString byteString = ByteString.copyFrom(entry.getValue().toByteArray());
+                    segmentMetadataBuilder.putDelayedIndexBitMap(entry.getKey(), byteString);
+                    iterator.remove();
+                }
+
+                segmentMetadataList.add(segmentMetadataBuilder.build());
+                segmentMetadataBuilder.clear();
+
+                bucketSnapshotSegments.add(snapshotSegmentBuilder.build());
+                snapshotSegmentBuilder.clear();
+            }
+        }
+
+        SnapshotMetadata bucketSnapshotMetadata = SnapshotMetadata.newBuilder()
+                .addAllMetadataList(segmentMetadataList)
+                .build();
+
+        final int lastSegmentEntryId = segmentMetadataList.size();
+
+        Bucket bucket = this.createImmutableBucket(startLedgerId, endLedgerId);
+        bucket.setCurrentSegmentEntryId(1);
+        bucket.setNumberBucketDelayedMessages(numMessages);
+        bucket.setLastSegmentEntryId(lastSegmentEntryId);
+
+        // Add the first snapshot segment last message to snapshotSegmentLastMessageTable
+        checkArgument(!bucketSnapshotSegments.isEmpty());
+        SnapshotSegment snapshotSegment = bucketSnapshotSegments.get(0);
+        DelayedIndex delayedIndex = snapshotSegment.getIndexes(snapshotSegment.getIndexesCount() - 1);
+        snapshotSegmentLastIndexTable.put(delayedIndex.getLedgerId(), delayedIndex.getEntryId(), bucket);
+
+        if (log.isDebugEnabled()) {
+            log.debug("[{}] Create bucket snapshot, bucket: {}", dispatcher.getName(), bucket);
+        }
+
+        String bucketKey = bucket.bucketKey();
+        CompletableFuture<Long> future = asyncSaveBucketSnapshot(bucketKey,
+                bucketSnapshotMetadata, bucketSnapshotSegments);
+        bucket.setSnapshotCreateFuture(future);
+        future.whenComplete((__, ex) -> {
+            if (ex == null) {
+                bucket.setSnapshotCreateFuture(null);
+            } else {
+                //TODO Record create snapshot failed
+                log.error("Failed to create snapshot: ", ex);
+            }
+        });
+
+        return future;
+    }
+
+
+    @SneakyThrows
+    private CompletableFuture<Void> asyncLoadNextBucketSnapshotEntry(Bucket bucket, boolean isRebuild) {
+        if (log.isDebugEnabled()) {
+            log.debug("[{}] Load next bucket snapshot data, bucket: {}", dispatcher.getName(), bucket);
+        }
+        if (bucket == null) {
+            return CompletableFuture.completedFuture(null);
+        }
+
+        final CompletableFuture<Long> createFuture = bucket.snapshotCreateFuture;
+        if (createFuture != null) {
+            // Wait bucket snapshot create finish
+            createFuture.get();
+        }
+
+        final String bucketKey = bucket.bucketKey();
+        final Long bucketId = getBucketIdByBucketKey(bucketKey);
+        Objects.requireNonNull(bucketId);
+
+        CompletableFuture<Integer> loadMetaDataFuture = new CompletableFuture<>();
+        if (isRebuild) {
+            final long cutoffTime = getCutoffTime();
+            // Load Metadata of bucket snapshot
+            bucketSnapshotStorage.getBucketSnapshotMetadata(bucketId).thenAccept(snapshotMetadata -> {

Review Comment:
   If this method got any exception, `loadMetaDataFuture` will not be complete.



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/BucketDelayedDeliveryTracker.java:
##########
@@ -0,0 +1,628 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static org.apache.bookkeeper.mledger.util.Futures.executeWithRetry;
+import com.google.common.collect.HashBasedTable;
+import com.google.common.collect.Range;
+import com.google.common.collect.RangeMap;
+import com.google.common.collect.Table;
+import com.google.common.collect.TreeRangeMap;
+import com.google.protobuf.ByteString;
+import io.netty.util.Timeout;
+import io.netty.util.Timer;
+import java.time.Clock;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.concurrent.CompletableFuture;
+import javax.annotation.concurrent.ThreadSafe;
+import lombok.SneakyThrows;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.bookkeeper.mledger.ManagedCursor;
+import org.apache.bookkeeper.mledger.ManagedLedgerException;
+import org.apache.bookkeeper.mledger.impl.PositionImpl;
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.lang.StringUtils;
+import org.apache.commons.lang3.mutable.MutableLong;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.DelayedIndex;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotMetadata;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegment;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+import org.apache.pulsar.broker.service.persistent.PersistentDispatcherMultipleConsumers;
+import org.apache.pulsar.common.util.FutureUtil;
+import org.apache.pulsar.common.util.collections.TripleLongPriorityQueue;
+
+@Slf4j
+@ThreadSafe
+public class BucketDelayedDeliveryTracker extends InMemoryDelayedDeliveryTracker {
+
+    public static final String DELAYED_BUCKET_KEY_PREFIX = "#pulsar.internal.delayed.bucket";
+
+    public static final String DELIMITER = "_";
+
+    private final long minIndexCountPerBucket;
+
+    private final long timeStepPerBucketSnapshotSegment;
+
+    private final int maxNumBuckets;
+
+    private final ManagedCursor cursor;
+
+    public final BucketSnapshotStorage bucketSnapshotStorage;
+
+    private long numberDelayedMessages;
+
+    private final Bucket lastMutableBucket;
+
+    private final TripleLongPriorityQueue sharedBucketPriorityQueue;
+
+    private final RangeMap<Long, Bucket> immutableBuckets;
+
+    private final Table<Long, Long, Bucket> snapshotSegmentLastIndexTable;
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        this(dispatcher, timer, tickTimeMillis, Clock.systemUTC(), isDelayedDeliveryDeliverAtTimeStrict,
+                bucketSnapshotStorage, minIndexCountPerBucket, timeStepPerBucketSnapshotSegment, maxNumBuckets);
+    }
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis, Clock clock,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        super(dispatcher, timer, tickTimeMillis, clock, isDelayedDeliveryDeliverAtTimeStrict);
+        this.minIndexCountPerBucket = minIndexCountPerBucket;
+        this.timeStepPerBucketSnapshotSegment = timeStepPerBucketSnapshotSegment;
+        this.maxNumBuckets = maxNumBuckets;
+        this.cursor = dispatcher.getCursor();
+        this.sharedBucketPriorityQueue = new TripleLongPriorityQueue();
+        this.immutableBuckets = TreeRangeMap.create();
+        this.snapshotSegmentLastIndexTable = HashBasedTable.create();
+
+        this.bucketSnapshotStorage = bucketSnapshotStorage;
+
+        numberDelayedMessages = recoverBucketSnapshot();
+
+        this.lastMutableBucket = new Bucket(-1L, -1L, new HashMap<>());
+    }
+
+    @SneakyThrows
+    private long recoverBucketSnapshot() {
+        List<CompletableFuture<Void>> completableFutures = new ArrayList<>();
+        this.cursor.getCursorProperties().keySet().forEach(key -> {
+            if (key.startsWith(DELAYED_BUCKET_KEY_PREFIX)) {
+                String[] keys = key.split(DELIMITER);
+                checkArgument(keys.length == 3);
+                Bucket bucket = createImmutableBucket(Long.parseLong(keys[1]), Long.parseLong(keys[2]));
+                completableFutures.add(asyncLoadNextBucketSnapshotEntry(bucket, true));
+            }
+        });
+
+        if (completableFutures.isEmpty()) {
+            return 0;
+        }
+
+        FutureUtil.waitForAll(completableFutures).get();
+
+        MutableLong numberDelayedMessages = new MutableLong(0);
+        immutableBuckets.asMapOfRanges().values().forEach(bucket -> {
+            numberDelayedMessages.add(bucket.numberBucketDelayedMessages);
+        });
+
+        log.info("[{}] Recover delayed message index bucket snapshot finish, buckets: {}, numberDelayedMessages: {}",
+                dispatcher.getName(), immutableBuckets.asMapOfRanges().size(), numberDelayedMessages.getValue());
+
+        return numberDelayedMessages.getValue();
+    }
+
+    private void moveScheduledMessageToSharedQueue(long cutoffTime) {
+        TripleLongPriorityQueue priorityQueue = getPriorityQueue();
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (timestamp > cutoffTime) {
+                break;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+            sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+
+            priorityQueue.pop();
+        }
+    }
+
+    @Override
+    public void run(Timeout timeout) throws Exception {
+        synchronized (this) {
+            moveScheduledMessageToSharedQueue(getCutoffTime());
+        }
+        super.run(timeout);
+    }
+
+    private Optional<Bucket> findBucket(long ledgerId) {
+        if (immutableBuckets.asMapOfRanges().isEmpty()) {
+            return Optional.empty();
+        }
+
+        Range<Long> span = immutableBuckets.span();
+        if (!span.contains(ledgerId)) {
+            return Optional.empty();
+        }
+        return Optional.ofNullable(immutableBuckets.get(ledgerId));
+    }
+
+    private Long getBucketIdByBucketKey(String bucketKey) {
+        String bucketIdStr = cursor.getCursorProperties().get(bucketKey);
+        if (StringUtils.isBlank(bucketIdStr)) {
+            return null;
+        }
+        return Long.valueOf(bucketIdStr);
+    }
+
+    private Bucket createImmutableBucket(long startLedgerId, long endLedgerId) {
+        Bucket newBucket = new Bucket(startLedgerId, endLedgerId, new HashMap<>());
+        immutableBuckets.put(Range.closed(startLedgerId, endLedgerId), newBucket);
+        return newBucket;
+    }
+
+    private CompletableFuture<Long> asyncSaveBucketSnapshot(
+            final String bucketKey, SnapshotMetadata snapshotMetadata,
+            List<SnapshotSegment> bucketSnapshotSegments) {
+        Long bucketId = getBucketIdByBucketKey(bucketKey);
+        checkArgument(bucketId == null);
+
+        return bucketSnapshotStorage.createBucketSnapshot(snapshotMetadata, bucketSnapshotSegments)
+                .thenCompose(newBucketId -> putBucketKeyId(bucketKey, newBucketId));
+    }
+
+    private CompletableFuture<Long> putBucketKeyId(String bucketKey, Long bucketId) {
+        Objects.requireNonNull(bucketId);
+        return executeWithRetry(() -> cursor.putCursorProperty(bucketKey, String.valueOf(bucketId)),
+                ManagedLedgerException.BadVersionException.class).thenApply(__ -> bucketId);
+    }
+
+    private CompletableFuture<Long> asyncCreateBucketSnapshot() {
+        TripleLongPriorityQueue priorityQueue = super.getPriorityQueue();
+        if (priorityQueue.isEmpty()) {
+            return CompletableFuture.completedFuture(null);
+        }
+        long numMessages = 0;
+
+        final long startLedgerId = lastMutableBucket.startLedgerId;
+        final long endLedgerId = lastMutableBucket.endLedgerId;
+
+        List<SnapshotSegment> bucketSnapshotSegments = new ArrayList<>();
+        List<SnapshotSegmentMetadata> segmentMetadataList = new ArrayList<>();
+        Map<Long, BitSet> bitMap = new HashMap<>();
+        SnapshotSegment.Builder snapshotSegmentBuilder = SnapshotSegment.newBuilder();
+        SnapshotSegmentMetadata.Builder segmentMetadataBuilder = SnapshotSegmentMetadata.newBuilder();
+
+        long currentTimestampUpperLimit = 0;
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (currentTimestampUpperLimit == 0) {
+                currentTimestampUpperLimit = timestamp + timeStepPerBucketSnapshotSegment - 1;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+
+            checkArgument(ledgerId >= startLedgerId && ledgerId <= endLedgerId);
+
+            // Move first segment of bucket snapshot to sharedBucketPriorityQueue
+            if (segmentMetadataList.size() == 0) {
+                sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+            }
+
+            priorityQueue.pop();
+            numMessages++;
+
+            DelayedIndex delayedIndex = DelayedIndex.newBuilder()
+                    .setTimestamp(timestamp)
+                    .setLedgerId(ledgerId)
+                    .setEntryId(entryId).build();
+
+            if (entryId <= Integer.MAX_VALUE) {
+                bitMap.compute(ledgerId, (k, v) -> new BitSet()).set((int) entryId);
+            }
+
+            snapshotSegmentBuilder.addIndexes(delayedIndex);
+
+            if (priorityQueue.isEmpty() || priorityQueue.peekN1() > currentTimestampUpperLimit) {
+                segmentMetadataBuilder.setMaxScheduleTimestamp(timestamp);
+                currentTimestampUpperLimit = 0;
+
+                Iterator<Map.Entry<Long, BitSet>> iterator = bitMap.entrySet().iterator();
+                while (iterator.hasNext()) {
+                    Map.Entry<Long, BitSet> entry = iterator.next();
+                    ByteString byteString = ByteString.copyFrom(entry.getValue().toByteArray());
+                    segmentMetadataBuilder.putDelayedIndexBitMap(entry.getKey(), byteString);
+                    iterator.remove();
+                }
+
+                segmentMetadataList.add(segmentMetadataBuilder.build());
+                segmentMetadataBuilder.clear();
+
+                bucketSnapshotSegments.add(snapshotSegmentBuilder.build());
+                snapshotSegmentBuilder.clear();
+            }
+        }
+
+        SnapshotMetadata bucketSnapshotMetadata = SnapshotMetadata.newBuilder()
+                .addAllMetadataList(segmentMetadataList)
+                .build();
+
+        final int lastSegmentEntryId = segmentMetadataList.size();
+
+        Bucket bucket = this.createImmutableBucket(startLedgerId, endLedgerId);
+        bucket.setCurrentSegmentEntryId(1);
+        bucket.setNumberBucketDelayedMessages(numMessages);
+        bucket.setLastSegmentEntryId(lastSegmentEntryId);
+
+        // Add the first snapshot segment last message to snapshotSegmentLastMessageTable
+        checkArgument(!bucketSnapshotSegments.isEmpty());
+        SnapshotSegment snapshotSegment = bucketSnapshotSegments.get(0);
+        DelayedIndex delayedIndex = snapshotSegment.getIndexes(snapshotSegment.getIndexesCount() - 1);
+        snapshotSegmentLastIndexTable.put(delayedIndex.getLedgerId(), delayedIndex.getEntryId(), bucket);
+
+        if (log.isDebugEnabled()) {
+            log.debug("[{}] Create bucket snapshot, bucket: {}", dispatcher.getName(), bucket);
+        }
+
+        String bucketKey = bucket.bucketKey();
+        CompletableFuture<Long> future = asyncSaveBucketSnapshot(bucketKey,
+                bucketSnapshotMetadata, bucketSnapshotSegments);
+        bucket.setSnapshotCreateFuture(future);
+        future.whenComplete((__, ex) -> {
+            if (ex == null) {
+                bucket.setSnapshotCreateFuture(null);
+            } else {
+                //TODO Record create snapshot failed
+                log.error("Failed to create snapshot: ", ex);
+            }
+        });
+
+        return future;
+    }
+
+
+    @SneakyThrows
+    private CompletableFuture<Void> asyncLoadNextBucketSnapshotEntry(Bucket bucket, boolean isRebuild) {
+        if (log.isDebugEnabled()) {
+            log.debug("[{}] Load next bucket snapshot data, bucket: {}", dispatcher.getName(), bucket);
+        }
+        if (bucket == null) {
+            return CompletableFuture.completedFuture(null);
+        }
+
+        final CompletableFuture<Long> createFuture = bucket.snapshotCreateFuture;
+        if (createFuture != null) {
+            // Wait bucket snapshot create finish
+            createFuture.get();
+        }
+
+        final String bucketKey = bucket.bucketKey();
+        final Long bucketId = getBucketIdByBucketKey(bucketKey);
+        Objects.requireNonNull(bucketId);
+
+        CompletableFuture<Integer> loadMetaDataFuture = new CompletableFuture<>();
+        if (isRebuild) {
+            final long cutoffTime = getCutoffTime();
+            // Load Metadata of bucket snapshot
+            bucketSnapshotStorage.getBucketSnapshotMetadata(bucketId).thenAccept(snapshotMetadata -> {
+                List<SnapshotSegmentMetadata> metadataList = snapshotMetadata.getMetadataListList();
+
+                // Skip all already reach schedule time snapshot segments
+                int nextSnapshotEntryIndex = 0;
+                while (nextSnapshotEntryIndex < metadataList.size()
+                        && metadataList.get(nextSnapshotEntryIndex).getMaxScheduleTimestamp() <= cutoffTime) {
+                    nextSnapshotEntryIndex++;
+                }
+
+                final int lastSegmentEntryId = metadataList.size();
+
+                long numberMessages = bucket.covertDelayIndexMapAndCount(nextSnapshotEntryIndex, metadataList);

Review Comment:
   It's an immutable bucket. Why can we modify it?



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/BucketDelayedDeliveryTracker.java:
##########
@@ -0,0 +1,565 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static org.apache.bookkeeper.mledger.util.Futures.executeWithRetry;
+import com.google.common.collect.HashBasedTable;
+import com.google.common.collect.Range;
+import com.google.common.collect.RangeMap;
+import com.google.common.collect.Table;
+import com.google.common.collect.TreeRangeMap;
+import com.google.protobuf.ByteString;
+import io.netty.util.Timeout;
+import io.netty.util.Timer;
+import java.time.Clock;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.concurrent.CompletableFuture;
+import javax.annotation.concurrent.ThreadSafe;
+import lombok.SneakyThrows;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.bookkeeper.mledger.ManagedCursor;
+import org.apache.bookkeeper.mledger.ManagedLedgerException;
+import org.apache.bookkeeper.mledger.impl.PositionImpl;
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.lang.StringUtils;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.DelayedIndex;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotMetadata;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegment;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+import org.apache.pulsar.broker.service.persistent.PersistentDispatcherMultipleConsumers;
+import org.apache.pulsar.common.util.collections.TripleLongPriorityQueue;
+
+@Slf4j
+@ThreadSafe
+public class BucketDelayedDeliveryTracker extends InMemoryDelayedDeliveryTracker {
+
+    public static final String DELAYED_BUCKET_KEY_PREFIX = "#pulsar.internal.delayed.bucket";
+
+    public static final String DELIMITER = "_";
+
+    private final long minIndexCountPerBucket;
+
+    private final long timeStepPerBucketSnapshotSegment;
+
+    private final int maxNumBuckets;
+
+    private final ManagedCursor cursor;
+
+    public final BucketSnapshotStorage bucketSnapshotStorage;
+
+    private long numberDelayedMessages;
+
+    private final Bucket lastMutableBucket;
+
+    private final TripleLongPriorityQueue sharedBucketPriorityQueue;
+
+    private final RangeMap<Long, Bucket> immutableBuckets;
+
+    private final Table<Long, Long, Bucket> snapshotSegmentLastIndexTable;
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 long fixedDelayDetectionLookahead,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        this(dispatcher, timer, tickTimeMillis, Clock.systemUTC(), isDelayedDeliveryDeliverAtTimeStrict,
+                fixedDelayDetectionLookahead,
+                bucketSnapshotStorage, minIndexCountPerBucket, timeStepPerBucketSnapshotSegment, maxNumBuckets);
+    }
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis, Clock clock,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 long fixedDelayDetectionLookahead,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        super(dispatcher, timer, tickTimeMillis, clock, isDelayedDeliveryDeliverAtTimeStrict,
+                fixedDelayDetectionLookahead);
+        this.minIndexCountPerBucket = minIndexCountPerBucket;
+        this.timeStepPerBucketSnapshotSegment = timeStepPerBucketSnapshotSegment;
+        this.maxNumBuckets = maxNumBuckets;
+        this.cursor = dispatcher.getCursor();
+        this.sharedBucketPriorityQueue = new TripleLongPriorityQueue();
+        this.immutableBuckets = TreeRangeMap.create();
+        this.snapshotSegmentLastIndexTable = HashBasedTable.create();
+
+        this.bucketSnapshotStorage = bucketSnapshotStorage;
+
+        numberDelayedMessages = 0L;
+
+        this.lastMutableBucket = new Bucket(-1L, -1L, new HashMap<>());
+    }
+
+    private void moveScheduledMessageToSharedQueue(long cutoffTime) {
+        TripleLongPriorityQueue priorityQueue = getPriorityQueue();
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (timestamp > cutoffTime) {
+                break;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+            sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+
+            priorityQueue.pop();
+        }
+    }
+
+    @Override
+    public void run(Timeout timeout) throws Exception {
+        synchronized (this) {
+            moveScheduledMessageToSharedQueue(getCutoffTime());
+        }
+        super.run(timeout);
+    }
+
+    private Optional<Bucket> findBucket(long ledgerId) {
+        if (immutableBuckets.asMapOfRanges().isEmpty()) {
+            return Optional.empty();
+        }
+
+        Range<Long> span = immutableBuckets.span();
+        if (!span.contains(ledgerId)) {
+            return Optional.empty();
+        }
+        return Optional.ofNullable(immutableBuckets.get(ledgerId));
+    }
+
+    private Long getBucketIdByBucketKey(String bucketKey) {
+        String bucketIdStr = cursor.getCursorProperties().get(bucketKey);
+        if (StringUtils.isBlank(bucketIdStr)) {
+            return null;
+        }
+        return Long.valueOf(bucketIdStr);
+    }
+
+    private Bucket createImmutableBucket(long startLedgerId, long endLedgerId) {
+        Bucket newBucket = new Bucket(startLedgerId, endLedgerId, new HashMap<>());
+        immutableBuckets.put(Range.closed(startLedgerId, endLedgerId), newBucket);
+        return newBucket;
+    }
+
+    private CompletableFuture<Long> asyncSaveBucketSnapshot(
+            final String bucketKey, SnapshotMetadata snapshotMetadata,
+            List<SnapshotSegment> bucketSnapshotSegments) {
+        Long bucketId = getBucketIdByBucketKey(bucketKey);
+        checkArgument(bucketId == null);
+
+        return bucketSnapshotStorage.createBucketSnapshot(snapshotMetadata, bucketSnapshotSegments)
+                .thenCompose(newBucketId -> putBucketKeyId(bucketKey, newBucketId));

Review Comment:
   If the retry operation failed, we may lose a bucket.



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/Bucket.java:
##########
@@ -0,0 +1,122 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static org.apache.pulsar.broker.delayed.BucketDelayedDeliveryTracker.DELAYED_BUCKET_KEY_PREFIX;
+import static org.apache.pulsar.broker.delayed.BucketDelayedDeliveryTracker.DELIMITER;
+import com.google.protobuf.ByteString;
+import java.util.BitSet;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.CompletableFuture;
+import lombok.AllArgsConstructor;
+import lombok.Data;
+import org.apache.commons.lang3.mutable.MutableLong;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+
+@Data
+@AllArgsConstructor
+public class Bucket {
+
+    long startLedgerId;
+    long endLedgerId;
+
+    Map<Long, BitSet> delayedIndexBitMap;
+
+    long numberBucketDelayedMessages;
+
+    int lastSegmentEntryId;
+
+    int currentSegmentEntryId;
+
+    long snapshotLength;
+
+    boolean active;
+
+    volatile CompletableFuture<Long> snapshotCreateFuture;
+
+    Bucket(long startLedgerId, long endLedgerId, Map<Long, BitSet> delayedIndexBitMap) {
+        this(startLedgerId, endLedgerId, delayedIndexBitMap, -1, -1, 0, 0, true, null);
+    }
+
+    long covertDelayIndexMapAndCount(int startSnapshotIndex, List<SnapshotSegmentMetadata> segmentMetadata) {
+        delayedIndexBitMap.clear();
+        MutableLong numberMessages = new MutableLong(0);
+        for (int i = startSnapshotIndex; i < segmentMetadata.size(); i++) {
+            Map<Long, ByteString> bitByteStringMap = segmentMetadata.get(i).getDelayedIndexBitMapMap();
+            bitByteStringMap.forEach((k, v) -> {
+                boolean exist = delayedIndexBitMap.containsKey(k);
+                byte[] bytes = v.toByteArray();
+                BitSet bitSet = BitSet.valueOf(bytes);
+                numberMessages.add(bitSet.cardinality());
+                if (!exist) {
+                    delayedIndexBitMap.put(k, bitSet);
+                } else {
+                    delayedIndexBitMap.get(k).or(bitSet);
+                }
+            });
+        }
+        return numberMessages.longValue();
+    }
+
+    boolean containsMessage(long ledgerId, int entryId) {
+        if (delayedIndexBitMap == null) {

Review Comment:
   Why we can allow users to put the map to null?



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/BucketDelayedDeliveryTracker.java:
##########
@@ -0,0 +1,628 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static org.apache.bookkeeper.mledger.util.Futures.executeWithRetry;
+import com.google.common.collect.HashBasedTable;
+import com.google.common.collect.Range;
+import com.google.common.collect.RangeMap;
+import com.google.common.collect.Table;
+import com.google.common.collect.TreeRangeMap;
+import com.google.protobuf.ByteString;
+import io.netty.util.Timeout;
+import io.netty.util.Timer;
+import java.time.Clock;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.concurrent.CompletableFuture;
+import javax.annotation.concurrent.ThreadSafe;
+import lombok.SneakyThrows;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.bookkeeper.mledger.ManagedCursor;
+import org.apache.bookkeeper.mledger.ManagedLedgerException;
+import org.apache.bookkeeper.mledger.impl.PositionImpl;
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.lang.StringUtils;
+import org.apache.commons.lang3.mutable.MutableLong;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.DelayedIndex;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotMetadata;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegment;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+import org.apache.pulsar.broker.service.persistent.PersistentDispatcherMultipleConsumers;
+import org.apache.pulsar.common.util.FutureUtil;
+import org.apache.pulsar.common.util.collections.TripleLongPriorityQueue;
+
+@Slf4j
+@ThreadSafe
+public class BucketDelayedDeliveryTracker extends InMemoryDelayedDeliveryTracker {
+
+    public static final String DELAYED_BUCKET_KEY_PREFIX = "#pulsar.internal.delayed.bucket";
+
+    public static final String DELIMITER = "_";
+
+    private final long minIndexCountPerBucket;
+
+    private final long timeStepPerBucketSnapshotSegment;
+
+    private final int maxNumBuckets;
+
+    private final ManagedCursor cursor;
+
+    public final BucketSnapshotStorage bucketSnapshotStorage;
+
+    private long numberDelayedMessages;
+
+    private final Bucket lastMutableBucket;
+
+    private final TripleLongPriorityQueue sharedBucketPriorityQueue;
+
+    private final RangeMap<Long, Bucket> immutableBuckets;
+
+    private final Table<Long, Long, Bucket> snapshotSegmentLastIndexTable;
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        this(dispatcher, timer, tickTimeMillis, Clock.systemUTC(), isDelayedDeliveryDeliverAtTimeStrict,
+                bucketSnapshotStorage, minIndexCountPerBucket, timeStepPerBucketSnapshotSegment, maxNumBuckets);
+    }
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis, Clock clock,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        super(dispatcher, timer, tickTimeMillis, clock, isDelayedDeliveryDeliverAtTimeStrict);
+        this.minIndexCountPerBucket = minIndexCountPerBucket;
+        this.timeStepPerBucketSnapshotSegment = timeStepPerBucketSnapshotSegment;
+        this.maxNumBuckets = maxNumBuckets;
+        this.cursor = dispatcher.getCursor();
+        this.sharedBucketPriorityQueue = new TripleLongPriorityQueue();
+        this.immutableBuckets = TreeRangeMap.create();
+        this.snapshotSegmentLastIndexTable = HashBasedTable.create();
+
+        this.bucketSnapshotStorage = bucketSnapshotStorage;
+
+        numberDelayedMessages = recoverBucketSnapshot();
+
+        this.lastMutableBucket = new Bucket(-1L, -1L, new HashMap<>());
+    }
+
+    @SneakyThrows
+    private long recoverBucketSnapshot() {
+        List<CompletableFuture<Void>> completableFutures = new ArrayList<>();
+        this.cursor.getCursorProperties().keySet().forEach(key -> {
+            if (key.startsWith(DELAYED_BUCKET_KEY_PREFIX)) {
+                String[] keys = key.split(DELIMITER);
+                checkArgument(keys.length == 3);
+                Bucket bucket = createImmutableBucket(Long.parseLong(keys[1]), Long.parseLong(keys[2]));
+                completableFutures.add(asyncLoadNextBucketSnapshotEntry(bucket, true));
+            }
+        });
+
+        if (completableFutures.isEmpty()) {
+            return 0;
+        }
+
+        FutureUtil.waitForAll(completableFutures).get();
+
+        MutableLong numberDelayedMessages = new MutableLong(0);
+        immutableBuckets.asMapOfRanges().values().forEach(bucket -> {
+            numberDelayedMessages.add(bucket.numberBucketDelayedMessages);
+        });
+
+        log.info("[{}] Recover delayed message index bucket snapshot finish, buckets: {}, numberDelayedMessages: {}",
+                dispatcher.getName(), immutableBuckets.asMapOfRanges().size(), numberDelayedMessages.getValue());
+
+        return numberDelayedMessages.getValue();
+    }
+
+    private void moveScheduledMessageToSharedQueue(long cutoffTime) {
+        TripleLongPriorityQueue priorityQueue = getPriorityQueue();
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (timestamp > cutoffTime) {
+                break;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+            sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+
+            priorityQueue.pop();
+        }
+    }
+
+    @Override
+    public void run(Timeout timeout) throws Exception {
+        synchronized (this) {
+            moveScheduledMessageToSharedQueue(getCutoffTime());
+        }
+        super.run(timeout);
+    }
+
+    private Optional<Bucket> findBucket(long ledgerId) {
+        if (immutableBuckets.asMapOfRanges().isEmpty()) {
+            return Optional.empty();
+        }
+
+        Range<Long> span = immutableBuckets.span();
+        if (!span.contains(ledgerId)) {
+            return Optional.empty();
+        }
+        return Optional.ofNullable(immutableBuckets.get(ledgerId));
+    }
+
+    private Long getBucketIdByBucketKey(String bucketKey) {
+        String bucketIdStr = cursor.getCursorProperties().get(bucketKey);
+        if (StringUtils.isBlank(bucketIdStr)) {
+            return null;
+        }
+        return Long.valueOf(bucketIdStr);
+    }
+
+    private Bucket createImmutableBucket(long startLedgerId, long endLedgerId) {
+        Bucket newBucket = new Bucket(startLedgerId, endLedgerId, new HashMap<>());

Review Comment:
   Do you consider moving` new HashMap<>()` to the construction method? because I don't see any other use cases.



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/BucketDelayedDeliveryTracker.java:
##########
@@ -0,0 +1,628 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static org.apache.bookkeeper.mledger.util.Futures.executeWithRetry;
+import com.google.common.collect.HashBasedTable;
+import com.google.common.collect.Range;
+import com.google.common.collect.RangeMap;
+import com.google.common.collect.Table;
+import com.google.common.collect.TreeRangeMap;
+import com.google.protobuf.ByteString;
+import io.netty.util.Timeout;
+import io.netty.util.Timer;
+import java.time.Clock;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.concurrent.CompletableFuture;
+import javax.annotation.concurrent.ThreadSafe;
+import lombok.SneakyThrows;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.bookkeeper.mledger.ManagedCursor;
+import org.apache.bookkeeper.mledger.ManagedLedgerException;
+import org.apache.bookkeeper.mledger.impl.PositionImpl;
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.lang.StringUtils;
+import org.apache.commons.lang3.mutable.MutableLong;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.DelayedIndex;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotMetadata;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegment;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+import org.apache.pulsar.broker.service.persistent.PersistentDispatcherMultipleConsumers;
+import org.apache.pulsar.common.util.FutureUtil;
+import org.apache.pulsar.common.util.collections.TripleLongPriorityQueue;
+
+@Slf4j
+@ThreadSafe
+public class BucketDelayedDeliveryTracker extends InMemoryDelayedDeliveryTracker {
+
+    public static final String DELAYED_BUCKET_KEY_PREFIX = "#pulsar.internal.delayed.bucket";
+
+    public static final String DELIMITER = "_";
+
+    private final long minIndexCountPerBucket;
+
+    private final long timeStepPerBucketSnapshotSegment;
+
+    private final int maxNumBuckets;
+
+    private final ManagedCursor cursor;
+
+    public final BucketSnapshotStorage bucketSnapshotStorage;
+
+    private long numberDelayedMessages;
+
+    private final Bucket lastMutableBucket;
+
+    private final TripleLongPriorityQueue sharedBucketPriorityQueue;
+
+    private final RangeMap<Long, Bucket> immutableBuckets;
+
+    private final Table<Long, Long, Bucket> snapshotSegmentLastIndexTable;
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        this(dispatcher, timer, tickTimeMillis, Clock.systemUTC(), isDelayedDeliveryDeliverAtTimeStrict,
+                bucketSnapshotStorage, minIndexCountPerBucket, timeStepPerBucketSnapshotSegment, maxNumBuckets);
+    }
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis, Clock clock,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        super(dispatcher, timer, tickTimeMillis, clock, isDelayedDeliveryDeliverAtTimeStrict);
+        this.minIndexCountPerBucket = minIndexCountPerBucket;
+        this.timeStepPerBucketSnapshotSegment = timeStepPerBucketSnapshotSegment;
+        this.maxNumBuckets = maxNumBuckets;
+        this.cursor = dispatcher.getCursor();
+        this.sharedBucketPriorityQueue = new TripleLongPriorityQueue();
+        this.immutableBuckets = TreeRangeMap.create();
+        this.snapshotSegmentLastIndexTable = HashBasedTable.create();
+
+        this.bucketSnapshotStorage = bucketSnapshotStorage;
+
+        numberDelayedMessages = recoverBucketSnapshot();
+
+        this.lastMutableBucket = new Bucket(-1L, -1L, new HashMap<>());
+    }
+
+    @SneakyThrows
+    private long recoverBucketSnapshot() {
+        List<CompletableFuture<Void>> completableFutures = new ArrayList<>();
+        this.cursor.getCursorProperties().keySet().forEach(key -> {
+            if (key.startsWith(DELAYED_BUCKET_KEY_PREFIX)) {

Review Comment:
   Would you like the `BucketKey` class?



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/BucketDelayedDeliveryTracker.java:
##########
@@ -0,0 +1,565 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static org.apache.bookkeeper.mledger.util.Futures.executeWithRetry;
+import com.google.common.collect.HashBasedTable;
+import com.google.common.collect.Range;
+import com.google.common.collect.RangeMap;
+import com.google.common.collect.Table;
+import com.google.common.collect.TreeRangeMap;
+import com.google.protobuf.ByteString;
+import io.netty.util.Timeout;
+import io.netty.util.Timer;
+import java.time.Clock;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.concurrent.CompletableFuture;
+import javax.annotation.concurrent.ThreadSafe;
+import lombok.SneakyThrows;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.bookkeeper.mledger.ManagedCursor;
+import org.apache.bookkeeper.mledger.ManagedLedgerException;
+import org.apache.bookkeeper.mledger.impl.PositionImpl;
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.lang.StringUtils;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.DelayedIndex;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotMetadata;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegment;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+import org.apache.pulsar.broker.service.persistent.PersistentDispatcherMultipleConsumers;
+import org.apache.pulsar.common.util.collections.TripleLongPriorityQueue;
+
+@Slf4j
+@ThreadSafe
+public class BucketDelayedDeliveryTracker extends InMemoryDelayedDeliveryTracker {
+
+    public static final String DELAYED_BUCKET_KEY_PREFIX = "#pulsar.internal.delayed.bucket";
+
+    public static final String DELIMITER = "_";
+
+    private final long minIndexCountPerBucket;
+
+    private final long timeStepPerBucketSnapshotSegment;
+
+    private final int maxNumBuckets;
+
+    private final ManagedCursor cursor;
+
+    public final BucketSnapshotStorage bucketSnapshotStorage;
+
+    private long numberDelayedMessages;
+
+    private final Bucket lastMutableBucket;
+
+    private final TripleLongPriorityQueue sharedBucketPriorityQueue;
+
+    private final RangeMap<Long, Bucket> immutableBuckets;
+
+    private final Table<Long, Long, Bucket> snapshotSegmentLastIndexTable;
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 long fixedDelayDetectionLookahead,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        this(dispatcher, timer, tickTimeMillis, Clock.systemUTC(), isDelayedDeliveryDeliverAtTimeStrict,
+                fixedDelayDetectionLookahead,
+                bucketSnapshotStorage, minIndexCountPerBucket, timeStepPerBucketSnapshotSegment, maxNumBuckets);
+    }
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis, Clock clock,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 long fixedDelayDetectionLookahead,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        super(dispatcher, timer, tickTimeMillis, clock, isDelayedDeliveryDeliverAtTimeStrict,
+                fixedDelayDetectionLookahead);
+        this.minIndexCountPerBucket = minIndexCountPerBucket;
+        this.timeStepPerBucketSnapshotSegment = timeStepPerBucketSnapshotSegment;
+        this.maxNumBuckets = maxNumBuckets;
+        this.cursor = dispatcher.getCursor();
+        this.sharedBucketPriorityQueue = new TripleLongPriorityQueue();
+        this.immutableBuckets = TreeRangeMap.create();
+        this.snapshotSegmentLastIndexTable = HashBasedTable.create();
+
+        this.bucketSnapshotStorage = bucketSnapshotStorage;
+
+        numberDelayedMessages = 0L;
+
+        this.lastMutableBucket = new Bucket(-1L, -1L, new HashMap<>());
+    }
+
+    private void moveScheduledMessageToSharedQueue(long cutoffTime) {
+        TripleLongPriorityQueue priorityQueue = getPriorityQueue();
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (timestamp > cutoffTime) {
+                break;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+            sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+
+            priorityQueue.pop();
+        }
+    }
+
+    @Override
+    public void run(Timeout timeout) throws Exception {
+        synchronized (this) {
+            moveScheduledMessageToSharedQueue(getCutoffTime());
+        }
+        super.run(timeout);
+    }
+
+    private Optional<Bucket> findBucket(long ledgerId) {
+        if (immutableBuckets.asMapOfRanges().isEmpty()) {
+            return Optional.empty();
+        }
+
+        Range<Long> span = immutableBuckets.span();
+        if (!span.contains(ledgerId)) {
+            return Optional.empty();
+        }
+        return Optional.ofNullable(immutableBuckets.get(ledgerId));
+    }
+
+    private Long getBucketIdByBucketKey(String bucketKey) {
+        String bucketIdStr = cursor.getCursorProperties().get(bucketKey);
+        if (StringUtils.isBlank(bucketIdStr)) {
+            return null;
+        }
+        return Long.valueOf(bucketIdStr);
+    }
+
+    private Bucket createImmutableBucket(long startLedgerId, long endLedgerId) {
+        Bucket newBucket = new Bucket(startLedgerId, endLedgerId, new HashMap<>());
+        immutableBuckets.put(Range.closed(startLedgerId, endLedgerId), newBucket);
+        return newBucket;
+    }
+
+    private CompletableFuture<Long> asyncSaveBucketSnapshot(
+            final String bucketKey, SnapshotMetadata snapshotMetadata,
+            List<SnapshotSegment> bucketSnapshotSegments) {
+        Long bucketId = getBucketIdByBucketKey(bucketKey);
+        checkArgument(bucketId == null);
+
+        return bucketSnapshotStorage.createBucketSnapshot(snapshotMetadata, bucketSnapshotSegments)
+                .thenCompose(newBucketId -> putBucketKeyId(bucketKey, newBucketId));
+    }
+
+    private CompletableFuture<Long> putBucketKeyId(String bucketKey, Long bucketId) {
+        Objects.requireNonNull(bucketId);
+        return executeWithRetry(() -> cursor.putCursorProperty(bucketKey, String.valueOf(bucketId)),
+                ManagedLedgerException.BadVersionException.class).thenApply(__ -> bucketId);
+    }
+
+    private CompletableFuture<Long> asyncCreateBucketSnapshot() {
+        TripleLongPriorityQueue priorityQueue = super.getPriorityQueue();
+        if (priorityQueue.isEmpty()) {
+            return CompletableFuture.completedFuture(null);
+        }
+        long numMessages = 0;
+
+        final long startLedgerId = lastMutableBucket.startLedgerId;
+        final long endLedgerId = lastMutableBucket.endLedgerId;
+
+        List<SnapshotSegment> bucketSnapshotSegments = new ArrayList<>();
+        List<SnapshotSegmentMetadata> segmentMetadataList = new ArrayList<>();
+        Map<Long, BitSet> bitMap = new HashMap<>();
+        SnapshotSegment.Builder snapshotSegmentBuilder = SnapshotSegment.newBuilder();
+        SnapshotSegmentMetadata.Builder segmentMetadataBuilder = SnapshotSegmentMetadata.newBuilder();
+
+        long currentTimestampUpperLimit = 0;
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (currentTimestampUpperLimit == 0) {
+                currentTimestampUpperLimit = timestamp + timeStepPerBucketSnapshotSegment - 1;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+
+            checkArgument(ledgerId >= startLedgerId && ledgerId <= endLedgerId);
+
+            // Move first segment of bucket snapshot to sharedBucketPriorityQueue
+            if (segmentMetadataList.size() == 0) {
+                sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+            }
+
+            priorityQueue.pop();
+            numMessages++;
+
+            DelayedIndex delayedIndex = DelayedIndex.newBuilder()
+                    .setTimestamp(timestamp)
+                    .setLedgerId(ledgerId)
+                    .setEntryId(entryId).build();
+
+            if (entryId <= Integer.MAX_VALUE) {
+                bitMap.compute(ledgerId, (k, v) -> new BitSet()).set((int) entryId);
+            }
+
+            snapshotSegmentBuilder.addIndexes(delayedIndex);
+
+            if (priorityQueue.isEmpty() || priorityQueue.peekN1() > currentTimestampUpperLimit) {
+                segmentMetadataBuilder.setMaxScheduleTimestamp(timestamp);
+                currentTimestampUpperLimit = 0;
+
+                Iterator<Map.Entry<Long, BitSet>> iterator = bitMap.entrySet().iterator();
+                while (iterator.hasNext()) {
+                    Map.Entry<Long, BitSet> entry = iterator.next();
+                    ByteString byteString = ByteString.copyFrom(entry.getValue().toByteArray());
+                    segmentMetadataBuilder.putDelayedIndexBitMap(entry.getKey(), byteString);
+                    iterator.remove();
+                }
+
+                segmentMetadataList.add(segmentMetadataBuilder.build());
+                segmentMetadataBuilder.clear();
+
+                bucketSnapshotSegments.add(snapshotSegmentBuilder.build());
+                snapshotSegmentBuilder.clear();
+            }
+        }
+
+        SnapshotMetadata bucketSnapshotMetadata = SnapshotMetadata.newBuilder()
+                .addAllMetadataList(segmentMetadataList)
+                .build();
+
+        final int lastSegmentEntryId = segmentMetadataList.size();
+
+        Bucket bucket = this.createImmutableBucket(startLedgerId, endLedgerId);
+        bucket.setCurrentSegmentEntryId(1);
+        bucket.setNumberBucketDelayedMessages(numMessages);
+        bucket.setLastSegmentEntryId(lastSegmentEntryId);
+
+        // Add the first snapshot segment last message to snapshotSegmentLastMessageTable
+        checkArgument(!bucketSnapshotSegments.isEmpty());
+        SnapshotSegment snapshotSegment = bucketSnapshotSegments.get(0);
+        DelayedIndex delayedIndex = snapshotSegment.getIndexes(snapshotSegment.getIndexesCount() - 1);
+        snapshotSegmentLastIndexTable.put(delayedIndex.getLedgerId(), delayedIndex.getEntryId(), bucket);
+
+        if (log.isDebugEnabled()) {
+            log.debug("[{}] Create bucket snapshot, bucket: {}", dispatcher.getName(), bucket);
+        }
+
+        String bucketKey = bucket.bucketKey();
+        CompletableFuture<Long> future = asyncSaveBucketSnapshot(bucketKey,
+                bucketSnapshotMetadata, bucketSnapshotSegments);
+        bucket.setSnapshotCreateFuture(future);
+        future.whenComplete((__, ex) -> {
+            if (ex == null) {
+                bucket.setSnapshotCreateFuture(null);
+            } else {
+                //TODO Record create snapshot failed
+                log.error("Failed to create snapshot: ", ex);
+            }
+        });
+
+        return future;
+    }
+
+
+    @SneakyThrows
+    private CompletableFuture<Void> asyncLoadNextBucketSnapshotEntry(Bucket bucket, boolean isRecover) {
+        if (log.isDebugEnabled()) {
+            log.debug("[{}] Load next bucket snapshot data, bucket: {}", dispatcher.getName(), bucket);
+        }
+        if (bucket == null) {
+            return CompletableFuture.completedFuture(null);
+        }
+
+        final CompletableFuture<Long> createFuture = bucket.snapshotCreateFuture;
+        if (createFuture != null) {
+            // Wait bucket snapshot create finish
+            createFuture.get();
+        }
+
+        final String bucketKey = bucket.bucketKey();
+        final Long bucketId = getBucketIdByBucketKey(bucketKey);
+        Objects.requireNonNull(bucketId);
+
+        CompletableFuture<Integer> loadMetaDataFuture = new CompletableFuture<>();
+        if (isRecover) {
+            // TODO Recover bucket snapshot
+        } else {
+            loadMetaDataFuture.complete(bucket.currentSegmentEntryId + 1);
+        }
+
+        CompletableFuture<Void> future = loadMetaDataFuture.thenCompose(nextSegmentEntryId -> {
+            if (nextSegmentEntryId > bucket.lastSegmentEntryId) {
+                // TODO Delete bucket snapshot
+                return CompletableFuture.completedFuture(null);
+            }
+
+            return bucketSnapshotStorage.getBucketSnapshotSegment(bucketId, nextSegmentEntryId, nextSegmentEntryId)
+                    .thenAccept(bucketSnapshotSegments -> {
+                        if (CollectionUtils.isEmpty(bucketSnapshotSegments)) {
+                            return;
+                        }
+
+                        SnapshotSegment snapshotSegment = bucketSnapshotSegments.get(0);
+                        List<DelayedIndex> indexList = snapshotSegment.getIndexesList();
+                        DelayedIndex lastDelayedIndex = indexList.get(indexList.size() - 1);
+
+                        this.snapshotSegmentLastIndexTable.put(lastDelayedIndex.getLedgerId(),
+                                lastDelayedIndex.getEntryId(), bucket);
+
+                        for (DelayedIndex index : indexList) {
+                            sharedBucketPriorityQueue.add(index.getTimestamp(), index.getLedgerId(),
+                                    index.getEntryId());
+                        }
+
+                        bucket.setCurrentSegmentEntryId(nextSegmentEntryId);
+                    });
+        });
+        return future;
+    }
+
+    private void resetLastMutableBucketRange() {
+        lastMutableBucket.setStartLedgerId(-1L);
+        lastMutableBucket.setEndLedgerId(-1L);
+    }
+
+    @Override
+    public synchronized boolean addMessage(long ledgerId, long entryId, long deliverAt) {
+        if (containsMessage(ledgerId, entryId)) {
+            messagesHaveFixedDelay = false;
+            return true;
+        }
+
+        if (deliverAt < 0 || deliverAt <= getCutoffTime()) {
+            messagesHaveFixedDelay = false;
+            return false;
+        }
+
+        boolean existBucket = findBucket(ledgerId).isPresent();
+
+        // Create bucket snapshot
+        if (ledgerId > lastMutableBucket.endLedgerId && !getPriorityQueue().isEmpty()) {
+            if (getPriorityQueue().size() >= minIndexCountPerBucket || existBucket) {
+                if (immutableBuckets.asMapOfRanges().size() >= maxNumBuckets) {
+                    // TODO merge bucket snapshot (synchronize operate)
+                }
+
+                asyncCreateBucketSnapshot();
+                resetLastMutableBucketRange();
+            }
+        }
+
+        if (ledgerId < lastMutableBucket.startLedgerId || existBucket) {
+            // If (ledgerId < startLedgerId || existBucket) means that message index belong to previous bucket range,
+            // enter sharedBucketPriorityQueue directly
+            sharedBucketPriorityQueue.add(deliverAt, ledgerId, entryId);
+        } else {
+            checkArgument(ledgerId >= lastMutableBucket.endLedgerId);
+
+            getPriorityQueue().add(deliverAt, ledgerId, entryId);
+
+            if (lastMutableBucket.startLedgerId == -1L) {
+                lastMutableBucket.setStartLedgerId(ledgerId);
+            }
+            lastMutableBucket.setEndLedgerId(ledgerId);
+        }
+
+        // TODO If the bitSet is sparse, this memory cost very high to deduplication and skip read message
+        lastMutableBucket.putIndexBit(ledgerId, entryId);
+        numberDelayedMessages++;
+
+        if (log.isDebugEnabled()) {
+            log.debug("[{}] Add message {}:{} -- Delivery in {} ms ", dispatcher.getName(), ledgerId, entryId,
+                    deliverAt - clock.millis());
+        }
+
+        updateTimer();
+
+        checkAndUpdateHighest(deliverAt);
+
+        return true;
+    }
+
+    @Override
+    public synchronized boolean hasMessageAvailable() {
+        long cutoffTime = getCutoffTime();
+
+        boolean hasMessageAvailable = !getPriorityQueue().isEmpty() && getPriorityQueue().peekN1() <= cutoffTime;
+
+        hasMessageAvailable = hasMessageAvailable
+                || !sharedBucketPriorityQueue.isEmpty() && sharedBucketPriorityQueue.peekN1() <= cutoffTime;
+        if (!hasMessageAvailable) {
+            updateTimer();
+        }
+        return hasMessageAvailable;
+    }
+
+    @Override
+    protected long nextDeliveryTime() {
+        if (getPriorityQueue().isEmpty() && !sharedBucketPriorityQueue.isEmpty()) {
+            return sharedBucketPriorityQueue.peekN1();
+        } else if (sharedBucketPriorityQueue.isEmpty() && !getPriorityQueue().isEmpty()) {
+            return getPriorityQueue().peekN1();
+        }
+        long timestamp = getPriorityQueue().peekN1();
+        long bucketTimestamp = sharedBucketPriorityQueue.peekN1();
+        return Math.min(timestamp, bucketTimestamp);
+    }
+
+    @Override
+    public synchronized long getNumberOfDelayedMessages() {
+        return numberDelayedMessages;
+    }
+
+    @Override
+    public synchronized long getBufferMemoryUsage() {
+        return getPriorityQueue().bytesCapacity() + sharedBucketPriorityQueue.bytesCapacity();
+    }
+
+    @Override
+    @SneakyThrows
+    public synchronized Set<PositionImpl> getScheduledMessages(int maxMessages) {
+        long cutoffTime = getCutoffTime();
+
+        moveScheduledMessageToSharedQueue(cutoffTime);
+
+        Set<PositionImpl> positions = new TreeSet<>();
+        int n = maxMessages;
+
+        while (n > 0 && !sharedBucketPriorityQueue.isEmpty()) {
+            long timestamp = sharedBucketPriorityQueue.peekN1();
+            if (timestamp > cutoffTime) {
+                break;
+            }
+
+            long ledgerId = sharedBucketPriorityQueue.peekN2();
+            long entryId = sharedBucketPriorityQueue.peekN3();
+            positions.add(new PositionImpl(ledgerId, entryId));
+
+            sharedBucketPriorityQueue.pop();
+            removeIndexBit(ledgerId, entryId);
+
+            Bucket bucket = snapshotSegmentLastIndexTable.remove(ledgerId, entryId);
+            if (bucket != null && bucket.active) {
+                if (log.isDebugEnabled()) {
+                    log.debug("[{}] Load next snapshot segment, bucket: {}", dispatcher.getName(), bucket);
+                }
+                // All message of current snapshot segment are scheduled, load next snapshot segment
+                asyncLoadNextBucketSnapshotEntry(bucket, false).get();
+            }
+
+            --n;
+            --numberDelayedMessages;
+        }
+
+        if (numberDelayedMessages <= 0) {
+            // Reset to initial state
+            highestDeliveryTimeTracked = 0;
+            messagesHaveFixedDelay = true;
+        }
+
+        updateTimer();
+
+        return positions;
+    }
+
+    @Override
+    @SneakyThrows
+    public synchronized void clear() {
+        super.clear();
+        cleanImmutableBuckets(true);
+        sharedBucketPriorityQueue.clear();
+        resetLastMutableBucketRange();
+        lastMutableBucket.delayedIndexBitMap.clear();
+        snapshotSegmentLastIndexTable.clear();
+        numberDelayedMessages = 0;
+    }
+
+    @Override
+    @SneakyThrows
+    public synchronized void close() {
+        super.close();
+        cleanImmutableBuckets(false);
+        lastMutableBucket.delayedIndexBitMap.clear();
+        sharedBucketPriorityQueue.close();
+    }
+
+    private void cleanImmutableBuckets(boolean delete) {
+        if (immutableBuckets != null) {
+            Iterator<Bucket> iterator = immutableBuckets.asMapOfRanges().values().iterator();
+            while (iterator.hasNext()) {
+                Bucket bucket = iterator.next();
+                if (bucket.delayedIndexBitMap != null) {
+                    bucket.delayedIndexBitMap.clear();
+                }
+                CompletableFuture<Long> snapshotGenerateFuture = bucket.snapshotCreateFuture;
+                if (snapshotGenerateFuture != null) {
+                    if (delete) {
+                        snapshotGenerateFuture.cancel(true);
+                        // TODO delete bucket snapshot
+                    } else {
+                        try {
+                            snapshotGenerateFuture.get();

Review Comment:
   It's better to add timeout.



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/BucketDelayedDeliveryTracker.java:
##########
@@ -0,0 +1,628 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static org.apache.bookkeeper.mledger.util.Futures.executeWithRetry;
+import com.google.common.collect.HashBasedTable;
+import com.google.common.collect.Range;
+import com.google.common.collect.RangeMap;
+import com.google.common.collect.Table;
+import com.google.common.collect.TreeRangeMap;
+import com.google.protobuf.ByteString;
+import io.netty.util.Timeout;
+import io.netty.util.Timer;
+import java.time.Clock;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.concurrent.CompletableFuture;
+import javax.annotation.concurrent.ThreadSafe;
+import lombok.SneakyThrows;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.bookkeeper.mledger.ManagedCursor;
+import org.apache.bookkeeper.mledger.ManagedLedgerException;
+import org.apache.bookkeeper.mledger.impl.PositionImpl;
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.lang.StringUtils;
+import org.apache.commons.lang3.mutable.MutableLong;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.DelayedIndex;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotMetadata;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegment;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+import org.apache.pulsar.broker.service.persistent.PersistentDispatcherMultipleConsumers;
+import org.apache.pulsar.common.util.FutureUtil;
+import org.apache.pulsar.common.util.collections.TripleLongPriorityQueue;
+
+@Slf4j
+@ThreadSafe
+public class BucketDelayedDeliveryTracker extends InMemoryDelayedDeliveryTracker {
+
+    public static final String DELAYED_BUCKET_KEY_PREFIX = "#pulsar.internal.delayed.bucket";
+
+    public static final String DELIMITER = "_";
+
+    private final long minIndexCountPerBucket;
+
+    private final long timeStepPerBucketSnapshotSegment;
+
+    private final int maxNumBuckets;
+
+    private final ManagedCursor cursor;
+
+    public final BucketSnapshotStorage bucketSnapshotStorage;
+
+    private long numberDelayedMessages;
+
+    private final Bucket lastMutableBucket;
+
+    private final TripleLongPriorityQueue sharedBucketPriorityQueue;
+
+    private final RangeMap<Long, Bucket> immutableBuckets;
+
+    private final Table<Long, Long, Bucket> snapshotSegmentLastIndexTable;
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        this(dispatcher, timer, tickTimeMillis, Clock.systemUTC(), isDelayedDeliveryDeliverAtTimeStrict,
+                bucketSnapshotStorage, minIndexCountPerBucket, timeStepPerBucketSnapshotSegment, maxNumBuckets);
+    }
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis, Clock clock,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        super(dispatcher, timer, tickTimeMillis, clock, isDelayedDeliveryDeliverAtTimeStrict);
+        this.minIndexCountPerBucket = minIndexCountPerBucket;
+        this.timeStepPerBucketSnapshotSegment = timeStepPerBucketSnapshotSegment;
+        this.maxNumBuckets = maxNumBuckets;
+        this.cursor = dispatcher.getCursor();
+        this.sharedBucketPriorityQueue = new TripleLongPriorityQueue();
+        this.immutableBuckets = TreeRangeMap.create();
+        this.snapshotSegmentLastIndexTable = HashBasedTable.create();
+
+        this.bucketSnapshotStorage = bucketSnapshotStorage;
+
+        numberDelayedMessages = recoverBucketSnapshot();
+
+        this.lastMutableBucket = new Bucket(-1L, -1L, new HashMap<>());
+    }
+
+    @SneakyThrows
+    private long recoverBucketSnapshot() {
+        List<CompletableFuture<Void>> completableFutures = new ArrayList<>();
+        this.cursor.getCursorProperties().keySet().forEach(key -> {
+            if (key.startsWith(DELAYED_BUCKET_KEY_PREFIX)) {
+                String[] keys = key.split(DELIMITER);
+                checkArgument(keys.length == 3);
+                Bucket bucket = createImmutableBucket(Long.parseLong(keys[1]), Long.parseLong(keys[2]));
+                completableFutures.add(asyncLoadNextBucketSnapshotEntry(bucket, true));
+            }
+        });
+
+        if (completableFutures.isEmpty()) {
+            return 0;
+        }
+
+        FutureUtil.waitForAll(completableFutures).get();
+
+        MutableLong numberDelayedMessages = new MutableLong(0);
+        immutableBuckets.asMapOfRanges().values().forEach(bucket -> {
+            numberDelayedMessages.add(bucket.numberBucketDelayedMessages);
+        });
+
+        log.info("[{}] Recover delayed message index bucket snapshot finish, buckets: {}, numberDelayedMessages: {}",
+                dispatcher.getName(), immutableBuckets.asMapOfRanges().size(), numberDelayedMessages.getValue());
+
+        return numberDelayedMessages.getValue();
+    }
+
+    private void moveScheduledMessageToSharedQueue(long cutoffTime) {
+        TripleLongPriorityQueue priorityQueue = getPriorityQueue();
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (timestamp > cutoffTime) {
+                break;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+            sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+
+            priorityQueue.pop();
+        }
+    }
+
+    @Override
+    public void run(Timeout timeout) throws Exception {
+        synchronized (this) {
+            moveScheduledMessageToSharedQueue(getCutoffTime());
+        }
+        super.run(timeout);
+    }
+
+    private Optional<Bucket> findBucket(long ledgerId) {
+        if (immutableBuckets.asMapOfRanges().isEmpty()) {
+            return Optional.empty();
+        }
+
+        Range<Long> span = immutableBuckets.span();
+        if (!span.contains(ledgerId)) {
+            return Optional.empty();
+        }
+        return Optional.ofNullable(immutableBuckets.get(ledgerId));
+    }
+
+    private Long getBucketIdByBucketKey(String bucketKey) {
+        String bucketIdStr = cursor.getCursorProperties().get(bucketKey);
+        if (StringUtils.isBlank(bucketIdStr)) {
+            return null;
+        }
+        return Long.valueOf(bucketIdStr);
+    }
+
+    private Bucket createImmutableBucket(long startLedgerId, long endLedgerId) {
+        Bucket newBucket = new Bucket(startLedgerId, endLedgerId, new HashMap<>());
+        immutableBuckets.put(Range.closed(startLedgerId, endLedgerId), newBucket);
+        return newBucket;
+    }
+
+    private CompletableFuture<Long> asyncSaveBucketSnapshot(
+            final String bucketKey, SnapshotMetadata snapshotMetadata,
+            List<SnapshotSegment> bucketSnapshotSegments) {
+        Long bucketId = getBucketIdByBucketKey(bucketKey);
+        checkArgument(bucketId == null);
+
+        return bucketSnapshotStorage.createBucketSnapshot(snapshotMetadata, bucketSnapshotSegments)
+                .thenCompose(newBucketId -> putBucketKeyId(bucketKey, newBucketId));
+    }
+
+    private CompletableFuture<Long> putBucketKeyId(String bucketKey, Long bucketId) {
+        Objects.requireNonNull(bucketId);
+        return executeWithRetry(() -> cursor.putCursorProperty(bucketKey, String.valueOf(bucketId)),
+                ManagedLedgerException.BadVersionException.class).thenApply(__ -> bucketId);
+    }
+
+    private CompletableFuture<Long> asyncCreateBucketSnapshot() {
+        TripleLongPriorityQueue priorityQueue = super.getPriorityQueue();
+        if (priorityQueue.isEmpty()) {
+            return CompletableFuture.completedFuture(null);

Review Comment:
   because we return `CompletableFuture<Long>`, if we return null it will have a risk to cause NPE.



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/Bucket.java:
##########
@@ -0,0 +1,122 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static org.apache.pulsar.broker.delayed.BucketDelayedDeliveryTracker.DELAYED_BUCKET_KEY_PREFIX;
+import static org.apache.pulsar.broker.delayed.BucketDelayedDeliveryTracker.DELIMITER;
+import com.google.protobuf.ByteString;
+import java.util.BitSet;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.CompletableFuture;
+import lombok.AllArgsConstructor;
+import lombok.Data;
+import org.apache.commons.lang3.mutable.MutableLong;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+
+@Data
+@AllArgsConstructor
+public class Bucket {
+
+    long startLedgerId;
+    long endLedgerId;
+
+    Map<Long, BitSet> delayedIndexBitMap;
+
+    long numberBucketDelayedMessages;
+
+    int lastSegmentEntryId;
+
+    int currentSegmentEntryId;
+
+    long snapshotLength;
+
+    boolean active;
+
+    volatile CompletableFuture<Long> snapshotCreateFuture;
+
+    Bucket(long startLedgerId, long endLedgerId, Map<Long, BitSet> delayedIndexBitMap) {
+        this(startLedgerId, endLedgerId, delayedIndexBitMap, -1, -1, 0, 0, true, null);
+    }
+
+    long covertDelayIndexMapAndCount(int startSnapshotIndex, List<SnapshotSegmentMetadata> segmentMetadata) {
+        delayedIndexBitMap.clear();
+        MutableLong numberMessages = new MutableLong(0);
+        for (int i = startSnapshotIndex; i < segmentMetadata.size(); i++) {
+            Map<Long, ByteString> bitByteStringMap = segmentMetadata.get(i).getDelayedIndexBitMapMap();
+            bitByteStringMap.forEach((k, v) -> {

Review Comment:
   Maybe change the `k` to `ledger` can help understand the logic...



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/BucketDelayedDeliveryTracker.java:
##########
@@ -0,0 +1,628 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static org.apache.bookkeeper.mledger.util.Futures.executeWithRetry;
+import com.google.common.collect.HashBasedTable;
+import com.google.common.collect.Range;
+import com.google.common.collect.RangeMap;
+import com.google.common.collect.Table;
+import com.google.common.collect.TreeRangeMap;
+import com.google.protobuf.ByteString;
+import io.netty.util.Timeout;
+import io.netty.util.Timer;
+import java.time.Clock;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.concurrent.CompletableFuture;
+import javax.annotation.concurrent.ThreadSafe;
+import lombok.SneakyThrows;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.bookkeeper.mledger.ManagedCursor;
+import org.apache.bookkeeper.mledger.ManagedLedgerException;
+import org.apache.bookkeeper.mledger.impl.PositionImpl;
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.lang.StringUtils;
+import org.apache.commons.lang3.mutable.MutableLong;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.DelayedIndex;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotMetadata;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegment;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+import org.apache.pulsar.broker.service.persistent.PersistentDispatcherMultipleConsumers;
+import org.apache.pulsar.common.util.FutureUtil;
+import org.apache.pulsar.common.util.collections.TripleLongPriorityQueue;
+
+@Slf4j
+@ThreadSafe
+public class BucketDelayedDeliveryTracker extends InMemoryDelayedDeliveryTracker {
+
+    public static final String DELAYED_BUCKET_KEY_PREFIX = "#pulsar.internal.delayed.bucket";
+
+    public static final String DELIMITER = "_";
+
+    private final long minIndexCountPerBucket;
+
+    private final long timeStepPerBucketSnapshotSegment;
+
+    private final int maxNumBuckets;
+
+    private final ManagedCursor cursor;
+
+    public final BucketSnapshotStorage bucketSnapshotStorage;
+
+    private long numberDelayedMessages;
+
+    private final Bucket lastMutableBucket;
+
+    private final TripleLongPriorityQueue sharedBucketPriorityQueue;
+
+    private final RangeMap<Long, Bucket> immutableBuckets;
+
+    private final Table<Long, Long, Bucket> snapshotSegmentLastIndexTable;
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        this(dispatcher, timer, tickTimeMillis, Clock.systemUTC(), isDelayedDeliveryDeliverAtTimeStrict,
+                bucketSnapshotStorage, minIndexCountPerBucket, timeStepPerBucketSnapshotSegment, maxNumBuckets);
+    }
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis, Clock clock,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        super(dispatcher, timer, tickTimeMillis, clock, isDelayedDeliveryDeliverAtTimeStrict);
+        this.minIndexCountPerBucket = minIndexCountPerBucket;
+        this.timeStepPerBucketSnapshotSegment = timeStepPerBucketSnapshotSegment;
+        this.maxNumBuckets = maxNumBuckets;
+        this.cursor = dispatcher.getCursor();
+        this.sharedBucketPriorityQueue = new TripleLongPriorityQueue();
+        this.immutableBuckets = TreeRangeMap.create();
+        this.snapshotSegmentLastIndexTable = HashBasedTable.create();
+
+        this.bucketSnapshotStorage = bucketSnapshotStorage;
+
+        numberDelayedMessages = recoverBucketSnapshot();
+
+        this.lastMutableBucket = new Bucket(-1L, -1L, new HashMap<>());
+    }
+
+    @SneakyThrows
+    private long recoverBucketSnapshot() {
+        List<CompletableFuture<Void>> completableFutures = new ArrayList<>();
+        this.cursor.getCursorProperties().keySet().forEach(key -> {
+            if (key.startsWith(DELAYED_BUCKET_KEY_PREFIX)) {
+                String[] keys = key.split(DELIMITER);
+                checkArgument(keys.length == 3);
+                Bucket bucket = createImmutableBucket(Long.parseLong(keys[1]), Long.parseLong(keys[2]));
+                completableFutures.add(asyncLoadNextBucketSnapshotEntry(bucket, true));
+            }
+        });
+
+        if (completableFutures.isEmpty()) {
+            return 0;
+        }
+
+        FutureUtil.waitForAll(completableFutures).get();
+
+        MutableLong numberDelayedMessages = new MutableLong(0);
+        immutableBuckets.asMapOfRanges().values().forEach(bucket -> {
+            numberDelayedMessages.add(bucket.numberBucketDelayedMessages);
+        });
+
+        log.info("[{}] Recover delayed message index bucket snapshot finish, buckets: {}, numberDelayedMessages: {}",
+                dispatcher.getName(), immutableBuckets.asMapOfRanges().size(), numberDelayedMessages.getValue());
+
+        return numberDelayedMessages.getValue();
+    }
+
+    private void moveScheduledMessageToSharedQueue(long cutoffTime) {
+        TripleLongPriorityQueue priorityQueue = getPriorityQueue();
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (timestamp > cutoffTime) {
+                break;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+            sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+
+            priorityQueue.pop();
+        }
+    }
+
+    @Override
+    public void run(Timeout timeout) throws Exception {
+        synchronized (this) {
+            moveScheduledMessageToSharedQueue(getCutoffTime());
+        }
+        super.run(timeout);
+    }
+
+    private Optional<Bucket> findBucket(long ledgerId) {
+        if (immutableBuckets.asMapOfRanges().isEmpty()) {
+            return Optional.empty();
+        }
+
+        Range<Long> span = immutableBuckets.span();
+        if (!span.contains(ledgerId)) {
+            return Optional.empty();
+        }
+        return Optional.ofNullable(immutableBuckets.get(ledgerId));
+    }
+
+    private Long getBucketIdByBucketKey(String bucketKey) {
+        String bucketIdStr = cursor.getCursorProperties().get(bucketKey);
+        if (StringUtils.isBlank(bucketIdStr)) {
+            return null;
+        }
+        return Long.valueOf(bucketIdStr);
+    }
+
+    private Bucket createImmutableBucket(long startLedgerId, long endLedgerId) {
+        Bucket newBucket = new Bucket(startLedgerId, endLedgerId, new HashMap<>());
+        immutableBuckets.put(Range.closed(startLedgerId, endLedgerId), newBucket);
+        return newBucket;
+    }
+
+    private CompletableFuture<Long> asyncSaveBucketSnapshot(
+            final String bucketKey, SnapshotMetadata snapshotMetadata,
+            List<SnapshotSegment> bucketSnapshotSegments) {
+        Long bucketId = getBucketIdByBucketKey(bucketKey);
+        checkArgument(bucketId == null);
+
+        return bucketSnapshotStorage.createBucketSnapshot(snapshotMetadata, bucketSnapshotSegments)
+                .thenCompose(newBucketId -> putBucketKeyId(bucketKey, newBucketId));
+    }
+
+    private CompletableFuture<Long> putBucketKeyId(String bucketKey, Long bucketId) {
+        Objects.requireNonNull(bucketId);
+        return executeWithRetry(() -> cursor.putCursorProperty(bucketKey, String.valueOf(bucketId)),
+                ManagedLedgerException.BadVersionException.class).thenApply(__ -> bucketId);
+    }
+
+    private CompletableFuture<Long> asyncCreateBucketSnapshot() {
+        TripleLongPriorityQueue priorityQueue = super.getPriorityQueue();
+        if (priorityQueue.isEmpty()) {
+            return CompletableFuture.completedFuture(null);
+        }
+        long numMessages = 0;
+
+        final long startLedgerId = lastMutableBucket.startLedgerId;
+        final long endLedgerId = lastMutableBucket.endLedgerId;
+
+        List<SnapshotSegment> bucketSnapshotSegments = new ArrayList<>();
+        List<SnapshotSegmentMetadata> segmentMetadataList = new ArrayList<>();
+        Map<Long, BitSet> bitMap = new HashMap<>();
+        SnapshotSegment.Builder snapshotSegmentBuilder = SnapshotSegment.newBuilder();
+        SnapshotSegmentMetadata.Builder segmentMetadataBuilder = SnapshotSegmentMetadata.newBuilder();
+
+        long currentTimestampUpperLimit = 0;
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (currentTimestampUpperLimit == 0) {
+                currentTimestampUpperLimit = timestamp + timeStepPerBucketSnapshotSegment - 1;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+
+            checkArgument(ledgerId >= startLedgerId && ledgerId <= endLedgerId);
+
+            // Move first segment of bucket snapshot to sharedBucketPriorityQueue
+            if (segmentMetadataList.size() == 0) {
+                sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+            }
+
+            priorityQueue.pop();
+            numMessages++;
+
+            DelayedIndex delayedIndex = DelayedIndex.newBuilder()
+                    .setTimestamp(timestamp)
+                    .setLedgerId(ledgerId)
+                    .setEntryId(entryId).build();
+
+            if (entryId <= Integer.MAX_VALUE) {

Review Comment:
   What happen when `entryId > Integer.MAX_VALUE`?



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/Bucket.java:
##########
@@ -0,0 +1,122 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static org.apache.pulsar.broker.delayed.BucketDelayedDeliveryTracker.DELAYED_BUCKET_KEY_PREFIX;
+import static org.apache.pulsar.broker.delayed.BucketDelayedDeliveryTracker.DELIMITER;
+import com.google.protobuf.ByteString;
+import java.util.BitSet;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.CompletableFuture;
+import lombok.AllArgsConstructor;
+import lombok.Data;
+import org.apache.commons.lang3.mutable.MutableLong;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+
+@Data
+@AllArgsConstructor
+public class Bucket {
+
+    long startLedgerId;
+    long endLedgerId;
+
+    Map<Long, BitSet> delayedIndexBitMap;
+
+    long numberBucketDelayedMessages;
+
+    int lastSegmentEntryId;
+
+    int currentSegmentEntryId;
+
+    long snapshotLength;
+
+    boolean active;
+
+    volatile CompletableFuture<Long> snapshotCreateFuture;
+
+    Bucket(long startLedgerId, long endLedgerId, Map<Long, BitSet> delayedIndexBitMap) {
+        this(startLedgerId, endLedgerId, delayedIndexBitMap, -1, -1, 0, 0, true, null);
+    }
+
+    long covertDelayIndexMapAndCount(int startSnapshotIndex, List<SnapshotSegmentMetadata> segmentMetadata) {
+        delayedIndexBitMap.clear();
+        MutableLong numberMessages = new MutableLong(0);
+        for (int i = startSnapshotIndex; i < segmentMetadata.size(); i++) {
+            Map<Long, ByteString> bitByteStringMap = segmentMetadata.get(i).getDelayedIndexBitMapMap();
+            bitByteStringMap.forEach((k, v) -> {
+                boolean exist = delayedIndexBitMap.containsKey(k);

Review Comment:
   Because we clear it at line 59, why do we have to check it again?



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/BucketDelayedDeliveryTracker.java:
##########
@@ -0,0 +1,628 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static org.apache.bookkeeper.mledger.util.Futures.executeWithRetry;
+import com.google.common.collect.HashBasedTable;
+import com.google.common.collect.Range;
+import com.google.common.collect.RangeMap;
+import com.google.common.collect.Table;
+import com.google.common.collect.TreeRangeMap;
+import com.google.protobuf.ByteString;
+import io.netty.util.Timeout;
+import io.netty.util.Timer;
+import java.time.Clock;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.concurrent.CompletableFuture;
+import javax.annotation.concurrent.ThreadSafe;
+import lombok.SneakyThrows;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.bookkeeper.mledger.ManagedCursor;
+import org.apache.bookkeeper.mledger.ManagedLedgerException;
+import org.apache.bookkeeper.mledger.impl.PositionImpl;
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.lang.StringUtils;
+import org.apache.commons.lang3.mutable.MutableLong;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.DelayedIndex;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotMetadata;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegment;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+import org.apache.pulsar.broker.service.persistent.PersistentDispatcherMultipleConsumers;
+import org.apache.pulsar.common.util.FutureUtil;
+import org.apache.pulsar.common.util.collections.TripleLongPriorityQueue;
+
+@Slf4j
+@ThreadSafe
+public class BucketDelayedDeliveryTracker extends InMemoryDelayedDeliveryTracker {
+
+    public static final String DELAYED_BUCKET_KEY_PREFIX = "#pulsar.internal.delayed.bucket";
+
+    public static final String DELIMITER = "_";
+
+    private final long minIndexCountPerBucket;
+
+    private final long timeStepPerBucketSnapshotSegment;
+
+    private final int maxNumBuckets;
+
+    private final ManagedCursor cursor;
+
+    public final BucketSnapshotStorage bucketSnapshotStorage;
+
+    private long numberDelayedMessages;
+
+    private final Bucket lastMutableBucket;
+
+    private final TripleLongPriorityQueue sharedBucketPriorityQueue;
+
+    private final RangeMap<Long, Bucket> immutableBuckets;
+
+    private final Table<Long, Long, Bucket> snapshotSegmentLastIndexTable;
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        this(dispatcher, timer, tickTimeMillis, Clock.systemUTC(), isDelayedDeliveryDeliverAtTimeStrict,
+                bucketSnapshotStorage, minIndexCountPerBucket, timeStepPerBucketSnapshotSegment, maxNumBuckets);
+    }
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis, Clock clock,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        super(dispatcher, timer, tickTimeMillis, clock, isDelayedDeliveryDeliverAtTimeStrict);
+        this.minIndexCountPerBucket = minIndexCountPerBucket;
+        this.timeStepPerBucketSnapshotSegment = timeStepPerBucketSnapshotSegment;
+        this.maxNumBuckets = maxNumBuckets;
+        this.cursor = dispatcher.getCursor();
+        this.sharedBucketPriorityQueue = new TripleLongPriorityQueue();
+        this.immutableBuckets = TreeRangeMap.create();
+        this.snapshotSegmentLastIndexTable = HashBasedTable.create();
+
+        this.bucketSnapshotStorage = bucketSnapshotStorage;
+
+        numberDelayedMessages = recoverBucketSnapshot();
+
+        this.lastMutableBucket = new Bucket(-1L, -1L, new HashMap<>());
+    }
+
+    @SneakyThrows
+    private long recoverBucketSnapshot() {
+        List<CompletableFuture<Void>> completableFutures = new ArrayList<>();
+        this.cursor.getCursorProperties().keySet().forEach(key -> {
+            if (key.startsWith(DELAYED_BUCKET_KEY_PREFIX)) {
+                String[] keys = key.split(DELIMITER);
+                checkArgument(keys.length == 3);
+                Bucket bucket = createImmutableBucket(Long.parseLong(keys[1]), Long.parseLong(keys[2]));
+                completableFutures.add(asyncLoadNextBucketSnapshotEntry(bucket, true));
+            }
+        });
+
+        if (completableFutures.isEmpty()) {
+            return 0;
+        }
+
+        FutureUtil.waitForAll(completableFutures).get();
+
+        MutableLong numberDelayedMessages = new MutableLong(0);
+        immutableBuckets.asMapOfRanges().values().forEach(bucket -> {
+            numberDelayedMessages.add(bucket.numberBucketDelayedMessages);
+        });
+
+        log.info("[{}] Recover delayed message index bucket snapshot finish, buckets: {}, numberDelayedMessages: {}",
+                dispatcher.getName(), immutableBuckets.asMapOfRanges().size(), numberDelayedMessages.getValue());
+
+        return numberDelayedMessages.getValue();
+    }
+
+    private void moveScheduledMessageToSharedQueue(long cutoffTime) {
+        TripleLongPriorityQueue priorityQueue = getPriorityQueue();
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (timestamp > cutoffTime) {
+                break;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+            sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+
+            priorityQueue.pop();
+        }
+    }
+
+    @Override
+    public void run(Timeout timeout) throws Exception {
+        synchronized (this) {
+            moveScheduledMessageToSharedQueue(getCutoffTime());
+        }
+        super.run(timeout);
+    }
+
+    private Optional<Bucket> findBucket(long ledgerId) {
+        if (immutableBuckets.asMapOfRanges().isEmpty()) {
+            return Optional.empty();
+        }
+
+        Range<Long> span = immutableBuckets.span();
+        if (!span.contains(ledgerId)) {
+            return Optional.empty();
+        }
+        return Optional.ofNullable(immutableBuckets.get(ledgerId));
+    }
+
+    private Long getBucketIdByBucketKey(String bucketKey) {
+        String bucketIdStr = cursor.getCursorProperties().get(bucketKey);
+        if (StringUtils.isBlank(bucketIdStr)) {
+            return null;
+        }
+        return Long.valueOf(bucketIdStr);
+    }
+
+    private Bucket createImmutableBucket(long startLedgerId, long endLedgerId) {
+        Bucket newBucket = new Bucket(startLedgerId, endLedgerId, new HashMap<>());
+        immutableBuckets.put(Range.closed(startLedgerId, endLedgerId), newBucket);
+        return newBucket;
+    }
+
+    private CompletableFuture<Long> asyncSaveBucketSnapshot(
+            final String bucketKey, SnapshotMetadata snapshotMetadata,
+            List<SnapshotSegment> bucketSnapshotSegments) {
+        Long bucketId = getBucketIdByBucketKey(bucketKey);
+        checkArgument(bucketId == null);
+
+        return bucketSnapshotStorage.createBucketSnapshot(snapshotMetadata, bucketSnapshotSegments)
+                .thenCompose(newBucketId -> putBucketKeyId(bucketKey, newBucketId));
+    }
+
+    private CompletableFuture<Long> putBucketKeyId(String bucketKey, Long bucketId) {
+        Objects.requireNonNull(bucketId);
+        return executeWithRetry(() -> cursor.putCursorProperty(bucketKey, String.valueOf(bucketId)),
+                ManagedLedgerException.BadVersionException.class).thenApply(__ -> bucketId);
+    }
+
+    private CompletableFuture<Long> asyncCreateBucketSnapshot() {
+        TripleLongPriorityQueue priorityQueue = super.getPriorityQueue();
+        if (priorityQueue.isEmpty()) {
+            return CompletableFuture.completedFuture(null);
+        }
+        long numMessages = 0;
+
+        final long startLedgerId = lastMutableBucket.startLedgerId;
+        final long endLedgerId = lastMutableBucket.endLedgerId;
+
+        List<SnapshotSegment> bucketSnapshotSegments = new ArrayList<>();
+        List<SnapshotSegmentMetadata> segmentMetadataList = new ArrayList<>();
+        Map<Long, BitSet> bitMap = new HashMap<>();
+        SnapshotSegment.Builder snapshotSegmentBuilder = SnapshotSegment.newBuilder();
+        SnapshotSegmentMetadata.Builder segmentMetadataBuilder = SnapshotSegmentMetadata.newBuilder();
+
+        long currentTimestampUpperLimit = 0;
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (currentTimestampUpperLimit == 0) {
+                currentTimestampUpperLimit = timestamp + timeStepPerBucketSnapshotSegment - 1;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+
+            checkArgument(ledgerId >= startLedgerId && ledgerId <= endLedgerId);
+
+            // Move first segment of bucket snapshot to sharedBucketPriorityQueue
+            if (segmentMetadataList.size() == 0) {
+                sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+            }
+
+            priorityQueue.pop();
+            numMessages++;
+
+            DelayedIndex delayedIndex = DelayedIndex.newBuilder()
+                    .setTimestamp(timestamp)
+                    .setLedgerId(ledgerId)
+                    .setEntryId(entryId).build();
+
+            if (entryId <= Integer.MAX_VALUE) {
+                bitMap.compute(ledgerId, (k, v) -> new BitSet()).set((int) entryId);
+            }
+
+            snapshotSegmentBuilder.addIndexes(delayedIndex);
+
+            if (priorityQueue.isEmpty() || priorityQueue.peekN1() > currentTimestampUpperLimit) {
+                segmentMetadataBuilder.setMaxScheduleTimestamp(timestamp);
+                currentTimestampUpperLimit = 0;
+
+                Iterator<Map.Entry<Long, BitSet>> iterator = bitMap.entrySet().iterator();
+                while (iterator.hasNext()) {
+                    Map.Entry<Long, BitSet> entry = iterator.next();
+                    ByteString byteString = ByteString.copyFrom(entry.getValue().toByteArray());
+                    segmentMetadataBuilder.putDelayedIndexBitMap(entry.getKey(), byteString);
+                    iterator.remove();
+                }
+
+                segmentMetadataList.add(segmentMetadataBuilder.build());
+                segmentMetadataBuilder.clear();
+
+                bucketSnapshotSegments.add(snapshotSegmentBuilder.build());
+                snapshotSegmentBuilder.clear();
+            }
+        }
+
+        SnapshotMetadata bucketSnapshotMetadata = SnapshotMetadata.newBuilder()
+                .addAllMetadataList(segmentMetadataList)
+                .build();
+
+        final int lastSegmentEntryId = segmentMetadataList.size();
+
+        Bucket bucket = this.createImmutableBucket(startLedgerId, endLedgerId);

Review Comment:
   If you create an immutable bucket and then we can set some things.  it will break the immutable sematic.



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/Bucket.java:
##########
@@ -0,0 +1,122 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static org.apache.pulsar.broker.delayed.BucketDelayedDeliveryTracker.DELAYED_BUCKET_KEY_PREFIX;
+import static org.apache.pulsar.broker.delayed.BucketDelayedDeliveryTracker.DELIMITER;
+import com.google.protobuf.ByteString;
+import java.util.BitSet;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.CompletableFuture;
+import lombok.AllArgsConstructor;
+import lombok.Data;
+import org.apache.commons.lang3.mutable.MutableLong;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+
+@Data
+@AllArgsConstructor
+public class Bucket {
+
+    long startLedgerId;
+    long endLedgerId;
+
+    Map<Long, BitSet> delayedIndexBitMap;
+
+    long numberBucketDelayedMessages;
+
+    int lastSegmentEntryId;
+
+    int currentSegmentEntryId;
+
+    long snapshotLength;
+
+    boolean active;
+
+    volatile CompletableFuture<Long> snapshotCreateFuture;
+
+    Bucket(long startLedgerId, long endLedgerId, Map<Long, BitSet> delayedIndexBitMap) {
+        this(startLedgerId, endLedgerId, delayedIndexBitMap, -1, -1, 0, 0, true, null);
+    }
+
+    long covertDelayIndexMapAndCount(int startSnapshotIndex, List<SnapshotSegmentMetadata> segmentMetadata) {
+        delayedIndexBitMap.clear();
+        MutableLong numberMessages = new MutableLong(0);
+        for (int i = startSnapshotIndex; i < segmentMetadata.size(); i++) {
+            Map<Long, ByteString> bitByteStringMap = segmentMetadata.get(i).getDelayedIndexBitMapMap();
+            bitByteStringMap.forEach((k, v) -> {
+                boolean exist = delayedIndexBitMap.containsKey(k);
+                byte[] bytes = v.toByteArray();
+                BitSet bitSet = BitSet.valueOf(bytes);
+                numberMessages.add(bitSet.cardinality());
+                if (!exist) {
+                    delayedIndexBitMap.put(k, bitSet);
+                } else {
+                    delayedIndexBitMap.get(k).or(bitSet);
+                }
+            });
+        }
+        return numberMessages.longValue();

Review Comment:
   Should we set `numberBucketDelayedMessages` here?



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/Bucket.java:
##########
@@ -0,0 +1,122 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static org.apache.pulsar.broker.delayed.BucketDelayedDeliveryTracker.DELAYED_BUCKET_KEY_PREFIX;
+import static org.apache.pulsar.broker.delayed.BucketDelayedDeliveryTracker.DELIMITER;
+import com.google.protobuf.ByteString;
+import java.util.BitSet;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.CompletableFuture;
+import lombok.AllArgsConstructor;
+import lombok.Data;
+import org.apache.commons.lang3.mutable.MutableLong;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+
+@Data
+@AllArgsConstructor
+public class Bucket {
+
+    long startLedgerId;
+    long endLedgerId;
+
+    Map<Long, BitSet> delayedIndexBitMap;
+
+    long numberBucketDelayedMessages;
+
+    int lastSegmentEntryId;
+
+    int currentSegmentEntryId;
+
+    long snapshotLength;
+
+    boolean active;
+
+    volatile CompletableFuture<Long> snapshotCreateFuture;
+
+    Bucket(long startLedgerId, long endLedgerId, Map<Long, BitSet> delayedIndexBitMap) {
+        this(startLedgerId, endLedgerId, delayedIndexBitMap, -1, -1, 0, 0, true, null);
+    }
+
+    long covertDelayIndexMapAndCount(int startSnapshotIndex, List<SnapshotSegmentMetadata> segmentMetadata) {
+        delayedIndexBitMap.clear();
+        MutableLong numberMessages = new MutableLong(0);
+        for (int i = startSnapshotIndex; i < segmentMetadata.size(); i++) {
+            Map<Long, ByteString> bitByteStringMap = segmentMetadata.get(i).getDelayedIndexBitMapMap();
+            bitByteStringMap.forEach((k, v) -> {
+                boolean exist = delayedIndexBitMap.containsKey(k);
+                byte[] bytes = v.toByteArray();
+                BitSet bitSet = BitSet.valueOf(bytes);
+                numberMessages.add(bitSet.cardinality());
+                if (!exist) {
+                    delayedIndexBitMap.put(k, bitSet);
+                } else {
+                    delayedIndexBitMap.get(k).or(bitSet);
+                }
+            });
+        }
+        return numberMessages.longValue();
+    }
+
+    boolean containsMessage(long ledgerId, int entryId) {
+        if (delayedIndexBitMap == null) {
+            return false;
+        }
+
+        BitSet bitSet = delayedIndexBitMap.get(ledgerId);
+        if (bitSet == null) {
+            return false;
+        }
+        return bitSet.get(entryId);
+    }
+
+    void putIndexBit(long ledgerId, long entryId) {
+        if (entryId < Integer.MAX_VALUE) {

Review Comment:
   Why we don't handle the `entryId >= Integer.MAX_VALUE`?



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/Bucket.java:
##########
@@ -0,0 +1,122 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static org.apache.pulsar.broker.delayed.BucketDelayedDeliveryTracker.DELAYED_BUCKET_KEY_PREFIX;
+import static org.apache.pulsar.broker.delayed.BucketDelayedDeliveryTracker.DELIMITER;
+import com.google.protobuf.ByteString;
+import java.util.BitSet;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.CompletableFuture;
+import lombok.AllArgsConstructor;
+import lombok.Data;
+import org.apache.commons.lang3.mutable.MutableLong;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+
+@Data
+@AllArgsConstructor
+public class Bucket {
+
+    long startLedgerId;
+    long endLedgerId;
+
+    Map<Long, BitSet> delayedIndexBitMap;
+
+    long numberBucketDelayedMessages;
+
+    int lastSegmentEntryId;
+
+    int currentSegmentEntryId;
+
+    long snapshotLength;
+
+    boolean active;
+
+    volatile CompletableFuture<Long> snapshotCreateFuture;
+
+    Bucket(long startLedgerId, long endLedgerId, Map<Long, BitSet> delayedIndexBitMap) {
+        this(startLedgerId, endLedgerId, delayedIndexBitMap, -1, -1, 0, 0, true, null);
+    }
+
+    long covertDelayIndexMapAndCount(int startSnapshotIndex, List<SnapshotSegmentMetadata> segmentMetadata) {
+        delayedIndexBitMap.clear();
+        MutableLong numberMessages = new MutableLong(0);
+        for (int i = startSnapshotIndex; i < segmentMetadata.size(); i++) {
+            Map<Long, ByteString> bitByteStringMap = segmentMetadata.get(i).getDelayedIndexBitMapMap();
+            bitByteStringMap.forEach((k, v) -> {
+                boolean exist = delayedIndexBitMap.containsKey(k);
+                byte[] bytes = v.toByteArray();
+                BitSet bitSet = BitSet.valueOf(bytes);
+                numberMessages.add(bitSet.cardinality());
+                if (!exist) {
+                    delayedIndexBitMap.put(k, bitSet);
+                } else {
+                    delayedIndexBitMap.get(k).or(bitSet);
+                }
+            });
+        }
+        return numberMessages.longValue();
+    }
+
+    boolean containsMessage(long ledgerId, int entryId) {
+        if (delayedIndexBitMap == null) {
+            return false;
+        }
+
+        BitSet bitSet = delayedIndexBitMap.get(ledgerId);
+        if (bitSet == null) {
+            return false;
+        }
+        return bitSet.get(entryId);
+    }
+
+    void putIndexBit(long ledgerId, long entryId) {
+        if (entryId < Integer.MAX_VALUE) {
+            delayedIndexBitMap.compute(ledgerId, (k, v) -> new BitSet()).set((int) entryId);

Review Comment:
   Should we use `computeIfAbsent`?



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/BucketDelayedDeliveryTracker.java:
##########
@@ -0,0 +1,628 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static org.apache.bookkeeper.mledger.util.Futures.executeWithRetry;
+import com.google.common.collect.HashBasedTable;
+import com.google.common.collect.Range;
+import com.google.common.collect.RangeMap;
+import com.google.common.collect.Table;
+import com.google.common.collect.TreeRangeMap;
+import com.google.protobuf.ByteString;
+import io.netty.util.Timeout;
+import io.netty.util.Timer;
+import java.time.Clock;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.concurrent.CompletableFuture;
+import javax.annotation.concurrent.ThreadSafe;
+import lombok.SneakyThrows;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.bookkeeper.mledger.ManagedCursor;
+import org.apache.bookkeeper.mledger.ManagedLedgerException;
+import org.apache.bookkeeper.mledger.impl.PositionImpl;
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.lang.StringUtils;
+import org.apache.commons.lang3.mutable.MutableLong;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.DelayedIndex;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotMetadata;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegment;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+import org.apache.pulsar.broker.service.persistent.PersistentDispatcherMultipleConsumers;
+import org.apache.pulsar.common.util.FutureUtil;
+import org.apache.pulsar.common.util.collections.TripleLongPriorityQueue;
+
+@Slf4j
+@ThreadSafe
+public class BucketDelayedDeliveryTracker extends InMemoryDelayedDeliveryTracker {
+
+    public static final String DELAYED_BUCKET_KEY_PREFIX = "#pulsar.internal.delayed.bucket";
+
+    public static final String DELIMITER = "_";
+
+    private final long minIndexCountPerBucket;
+
+    private final long timeStepPerBucketSnapshotSegment;
+
+    private final int maxNumBuckets;
+
+    private final ManagedCursor cursor;
+
+    public final BucketSnapshotStorage bucketSnapshotStorage;
+
+    private long numberDelayedMessages;
+
+    private final Bucket lastMutableBucket;
+
+    private final TripleLongPriorityQueue sharedBucketPriorityQueue;
+
+    private final RangeMap<Long, Bucket> immutableBuckets;
+
+    private final Table<Long, Long, Bucket> snapshotSegmentLastIndexTable;
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        this(dispatcher, timer, tickTimeMillis, Clock.systemUTC(), isDelayedDeliveryDeliverAtTimeStrict,
+                bucketSnapshotStorage, minIndexCountPerBucket, timeStepPerBucketSnapshotSegment, maxNumBuckets);
+    }
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis, Clock clock,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        super(dispatcher, timer, tickTimeMillis, clock, isDelayedDeliveryDeliverAtTimeStrict);
+        this.minIndexCountPerBucket = minIndexCountPerBucket;
+        this.timeStepPerBucketSnapshotSegment = timeStepPerBucketSnapshotSegment;
+        this.maxNumBuckets = maxNumBuckets;
+        this.cursor = dispatcher.getCursor();
+        this.sharedBucketPriorityQueue = new TripleLongPriorityQueue();
+        this.immutableBuckets = TreeRangeMap.create();
+        this.snapshotSegmentLastIndexTable = HashBasedTable.create();
+
+        this.bucketSnapshotStorage = bucketSnapshotStorage;
+
+        numberDelayedMessages = recoverBucketSnapshot();
+
+        this.lastMutableBucket = new Bucket(-1L, -1L, new HashMap<>());
+    }
+
+    @SneakyThrows

Review Comment:
   Why `@SneakyThrows`?



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/BucketDelayedDeliveryTracker.java:
##########
@@ -0,0 +1,628 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static org.apache.bookkeeper.mledger.util.Futures.executeWithRetry;
+import com.google.common.collect.HashBasedTable;
+import com.google.common.collect.Range;
+import com.google.common.collect.RangeMap;
+import com.google.common.collect.Table;
+import com.google.common.collect.TreeRangeMap;
+import com.google.protobuf.ByteString;
+import io.netty.util.Timeout;
+import io.netty.util.Timer;
+import java.time.Clock;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.concurrent.CompletableFuture;
+import javax.annotation.concurrent.ThreadSafe;
+import lombok.SneakyThrows;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.bookkeeper.mledger.ManagedCursor;
+import org.apache.bookkeeper.mledger.ManagedLedgerException;
+import org.apache.bookkeeper.mledger.impl.PositionImpl;
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.lang.StringUtils;
+import org.apache.commons.lang3.mutable.MutableLong;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.DelayedIndex;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotMetadata;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegment;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+import org.apache.pulsar.broker.service.persistent.PersistentDispatcherMultipleConsumers;
+import org.apache.pulsar.common.util.FutureUtil;
+import org.apache.pulsar.common.util.collections.TripleLongPriorityQueue;
+
+@Slf4j
+@ThreadSafe
+public class BucketDelayedDeliveryTracker extends InMemoryDelayedDeliveryTracker {
+
+    public static final String DELAYED_BUCKET_KEY_PREFIX = "#pulsar.internal.delayed.bucket";
+
+    public static final String DELIMITER = "_";
+
+    private final long minIndexCountPerBucket;
+
+    private final long timeStepPerBucketSnapshotSegment;
+
+    private final int maxNumBuckets;
+
+    private final ManagedCursor cursor;
+
+    public final BucketSnapshotStorage bucketSnapshotStorage;
+
+    private long numberDelayedMessages;
+
+    private final Bucket lastMutableBucket;
+
+    private final TripleLongPriorityQueue sharedBucketPriorityQueue;
+
+    private final RangeMap<Long, Bucket> immutableBuckets;
+
+    private final Table<Long, Long, Bucket> snapshotSegmentLastIndexTable;
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        this(dispatcher, timer, tickTimeMillis, Clock.systemUTC(), isDelayedDeliveryDeliverAtTimeStrict,
+                bucketSnapshotStorage, minIndexCountPerBucket, timeStepPerBucketSnapshotSegment, maxNumBuckets);
+    }
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis, Clock clock,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        super(dispatcher, timer, tickTimeMillis, clock, isDelayedDeliveryDeliverAtTimeStrict);
+        this.minIndexCountPerBucket = minIndexCountPerBucket;
+        this.timeStepPerBucketSnapshotSegment = timeStepPerBucketSnapshotSegment;
+        this.maxNumBuckets = maxNumBuckets;
+        this.cursor = dispatcher.getCursor();
+        this.sharedBucketPriorityQueue = new TripleLongPriorityQueue();
+        this.immutableBuckets = TreeRangeMap.create();
+        this.snapshotSegmentLastIndexTable = HashBasedTable.create();
+
+        this.bucketSnapshotStorage = bucketSnapshotStorage;
+
+        numberDelayedMessages = recoverBucketSnapshot();

Review Comment:
   `this.numberDelayedMessages` ?



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/BucketDelayedDeliveryTracker.java:
##########
@@ -0,0 +1,628 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static org.apache.bookkeeper.mledger.util.Futures.executeWithRetry;
+import com.google.common.collect.HashBasedTable;
+import com.google.common.collect.Range;
+import com.google.common.collect.RangeMap;
+import com.google.common.collect.Table;
+import com.google.common.collect.TreeRangeMap;
+import com.google.protobuf.ByteString;
+import io.netty.util.Timeout;
+import io.netty.util.Timer;
+import java.time.Clock;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.concurrent.CompletableFuture;
+import javax.annotation.concurrent.ThreadSafe;
+import lombok.SneakyThrows;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.bookkeeper.mledger.ManagedCursor;
+import org.apache.bookkeeper.mledger.ManagedLedgerException;
+import org.apache.bookkeeper.mledger.impl.PositionImpl;
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.lang.StringUtils;
+import org.apache.commons.lang3.mutable.MutableLong;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.DelayedIndex;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotMetadata;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegment;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+import org.apache.pulsar.broker.service.persistent.PersistentDispatcherMultipleConsumers;
+import org.apache.pulsar.common.util.FutureUtil;
+import org.apache.pulsar.common.util.collections.TripleLongPriorityQueue;
+
+@Slf4j
+@ThreadSafe
+public class BucketDelayedDeliveryTracker extends InMemoryDelayedDeliveryTracker {
+
+    public static final String DELAYED_BUCKET_KEY_PREFIX = "#pulsar.internal.delayed.bucket";
+
+    public static final String DELIMITER = "_";
+
+    private final long minIndexCountPerBucket;
+
+    private final long timeStepPerBucketSnapshotSegment;
+
+    private final int maxNumBuckets;
+
+    private final ManagedCursor cursor;
+
+    public final BucketSnapshotStorage bucketSnapshotStorage;
+
+    private long numberDelayedMessages;
+
+    private final Bucket lastMutableBucket;
+
+    private final TripleLongPriorityQueue sharedBucketPriorityQueue;
+
+    private final RangeMap<Long, Bucket> immutableBuckets;
+
+    private final Table<Long, Long, Bucket> snapshotSegmentLastIndexTable;
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        this(dispatcher, timer, tickTimeMillis, Clock.systemUTC(), isDelayedDeliveryDeliverAtTimeStrict,
+                bucketSnapshotStorage, minIndexCountPerBucket, timeStepPerBucketSnapshotSegment, maxNumBuckets);
+    }
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis, Clock clock,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        super(dispatcher, timer, tickTimeMillis, clock, isDelayedDeliveryDeliverAtTimeStrict);
+        this.minIndexCountPerBucket = minIndexCountPerBucket;
+        this.timeStepPerBucketSnapshotSegment = timeStepPerBucketSnapshotSegment;
+        this.maxNumBuckets = maxNumBuckets;
+        this.cursor = dispatcher.getCursor();
+        this.sharedBucketPriorityQueue = new TripleLongPriorityQueue();
+        this.immutableBuckets = TreeRangeMap.create();
+        this.snapshotSegmentLastIndexTable = HashBasedTable.create();
+
+        this.bucketSnapshotStorage = bucketSnapshotStorage;
+
+        numberDelayedMessages = recoverBucketSnapshot();
+
+        this.lastMutableBucket = new Bucket(-1L, -1L, new HashMap<>());
+    }
+
+    @SneakyThrows
+    private long recoverBucketSnapshot() {
+        List<CompletableFuture<Void>> completableFutures = new ArrayList<>();
+        this.cursor.getCursorProperties().keySet().forEach(key -> {
+            if (key.startsWith(DELAYED_BUCKET_KEY_PREFIX)) {
+                String[] keys = key.split(DELIMITER);
+                checkArgument(keys.length == 3);
+                Bucket bucket = createImmutableBucket(Long.parseLong(keys[1]), Long.parseLong(keys[2]));
+                completableFutures.add(asyncLoadNextBucketSnapshotEntry(bucket, true));
+            }
+        });
+
+        if (completableFutures.isEmpty()) {
+            return 0;
+        }
+
+        FutureUtil.waitForAll(completableFutures).get();
+
+        MutableLong numberDelayedMessages = new MutableLong(0);
+        immutableBuckets.asMapOfRanges().values().forEach(bucket -> {
+            numberDelayedMessages.add(bucket.numberBucketDelayedMessages);
+        });
+
+        log.info("[{}] Recover delayed message index bucket snapshot finish, buckets: {}, numberDelayedMessages: {}",
+                dispatcher.getName(), immutableBuckets.asMapOfRanges().size(), numberDelayedMessages.getValue());
+
+        return numberDelayedMessages.getValue();
+    }
+
+    private void moveScheduledMessageToSharedQueue(long cutoffTime) {
+        TripleLongPriorityQueue priorityQueue = getPriorityQueue();
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (timestamp > cutoffTime) {
+                break;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+            sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+
+            priorityQueue.pop();
+        }
+    }
+
+    @Override
+    public void run(Timeout timeout) throws Exception {
+        synchronized (this) {
+            moveScheduledMessageToSharedQueue(getCutoffTime());
+        }
+        super.run(timeout);
+    }
+
+    private Optional<Bucket> findBucket(long ledgerId) {
+        if (immutableBuckets.asMapOfRanges().isEmpty()) {
+            return Optional.empty();
+        }
+
+        Range<Long> span = immutableBuckets.span();
+        if (!span.contains(ledgerId)) {
+            return Optional.empty();
+        }
+        return Optional.ofNullable(immutableBuckets.get(ledgerId));
+    }
+
+    private Long getBucketIdByBucketKey(String bucketKey) {
+        String bucketIdStr = cursor.getCursorProperties().get(bucketKey);
+        if (StringUtils.isBlank(bucketIdStr)) {
+            return null;
+        }
+        return Long.valueOf(bucketIdStr);
+    }
+
+    private Bucket createImmutableBucket(long startLedgerId, long endLedgerId) {
+        Bucket newBucket = new Bucket(startLedgerId, endLedgerId, new HashMap<>());
+        immutableBuckets.put(Range.closed(startLedgerId, endLedgerId), newBucket);
+        return newBucket;
+    }
+
+    private CompletableFuture<Long> asyncSaveBucketSnapshot(
+            final String bucketKey, SnapshotMetadata snapshotMetadata,
+            List<SnapshotSegment> bucketSnapshotSegments) {
+        Long bucketId = getBucketIdByBucketKey(bucketKey);
+        checkArgument(bucketId == null);
+
+        return bucketSnapshotStorage.createBucketSnapshot(snapshotMetadata, bucketSnapshotSegments)
+                .thenCompose(newBucketId -> putBucketKeyId(bucketKey, newBucketId));
+    }
+
+    private CompletableFuture<Long> putBucketKeyId(String bucketKey, Long bucketId) {
+        Objects.requireNonNull(bucketId);
+        return executeWithRetry(() -> cursor.putCursorProperty(bucketKey, String.valueOf(bucketId)),
+                ManagedLedgerException.BadVersionException.class).thenApply(__ -> bucketId);
+    }
+
+    private CompletableFuture<Long> asyncCreateBucketSnapshot() {
+        TripleLongPriorityQueue priorityQueue = super.getPriorityQueue();
+        if (priorityQueue.isEmpty()) {
+            return CompletableFuture.completedFuture(null);
+        }
+        long numMessages = 0;
+
+        final long startLedgerId = lastMutableBucket.startLedgerId;
+        final long endLedgerId = lastMutableBucket.endLedgerId;
+
+        List<SnapshotSegment> bucketSnapshotSegments = new ArrayList<>();
+        List<SnapshotSegmentMetadata> segmentMetadataList = new ArrayList<>();
+        Map<Long, BitSet> bitMap = new HashMap<>();
+        SnapshotSegment.Builder snapshotSegmentBuilder = SnapshotSegment.newBuilder();
+        SnapshotSegmentMetadata.Builder segmentMetadataBuilder = SnapshotSegmentMetadata.newBuilder();
+
+        long currentTimestampUpperLimit = 0;
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (currentTimestampUpperLimit == 0) {
+                currentTimestampUpperLimit = timestamp + timeStepPerBucketSnapshotSegment - 1;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+
+            checkArgument(ledgerId >= startLedgerId && ledgerId <= endLedgerId);
+
+            // Move first segment of bucket snapshot to sharedBucketPriorityQueue
+            if (segmentMetadataList.size() == 0) {
+                sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+            }
+
+            priorityQueue.pop();
+            numMessages++;
+
+            DelayedIndex delayedIndex = DelayedIndex.newBuilder()
+                    .setTimestamp(timestamp)
+                    .setLedgerId(ledgerId)
+                    .setEntryId(entryId).build();
+
+            if (entryId <= Integer.MAX_VALUE) {
+                bitMap.compute(ledgerId, (k, v) -> new BitSet()).set((int) entryId);
+            }
+
+            snapshotSegmentBuilder.addIndexes(delayedIndex);
+
+            if (priorityQueue.isEmpty() || priorityQueue.peekN1() > currentTimestampUpperLimit) {
+                segmentMetadataBuilder.setMaxScheduleTimestamp(timestamp);
+                currentTimestampUpperLimit = 0;
+
+                Iterator<Map.Entry<Long, BitSet>> iterator = bitMap.entrySet().iterator();
+                while (iterator.hasNext()) {
+                    Map.Entry<Long, BitSet> entry = iterator.next();
+                    ByteString byteString = ByteString.copyFrom(entry.getValue().toByteArray());
+                    segmentMetadataBuilder.putDelayedIndexBitMap(entry.getKey(), byteString);
+                    iterator.remove();
+                }
+
+                segmentMetadataList.add(segmentMetadataBuilder.build());
+                segmentMetadataBuilder.clear();
+
+                bucketSnapshotSegments.add(snapshotSegmentBuilder.build());
+                snapshotSegmentBuilder.clear();
+            }
+        }
+
+        SnapshotMetadata bucketSnapshotMetadata = SnapshotMetadata.newBuilder()
+                .addAllMetadataList(segmentMetadataList)
+                .build();
+
+        final int lastSegmentEntryId = segmentMetadataList.size();
+
+        Bucket bucket = this.createImmutableBucket(startLedgerId, endLedgerId);
+        bucket.setCurrentSegmentEntryId(1);
+        bucket.setNumberBucketDelayedMessages(numMessages);
+        bucket.setLastSegmentEntryId(lastSegmentEntryId);
+
+        // Add the first snapshot segment last message to snapshotSegmentLastMessageTable
+        checkArgument(!bucketSnapshotSegments.isEmpty());
+        SnapshotSegment snapshotSegment = bucketSnapshotSegments.get(0);
+        DelayedIndex delayedIndex = snapshotSegment.getIndexes(snapshotSegment.getIndexesCount() - 1);
+        snapshotSegmentLastIndexTable.put(delayedIndex.getLedgerId(), delayedIndex.getEntryId(), bucket);
+
+        if (log.isDebugEnabled()) {
+            log.debug("[{}] Create bucket snapshot, bucket: {}", dispatcher.getName(), bucket);
+        }
+
+        String bucketKey = bucket.bucketKey();
+        CompletableFuture<Long> future = asyncSaveBucketSnapshot(bucketKey,
+                bucketSnapshotMetadata, bucketSnapshotSegments);
+        bucket.setSnapshotCreateFuture(future);
+        future.whenComplete((__, ex) -> {
+            if (ex == null) {
+                bucket.setSnapshotCreateFuture(null);
+            } else {
+                //TODO Record create snapshot failed
+                log.error("Failed to create snapshot: ", ex);
+            }
+        });
+
+        return future;
+    }
+
+
+    @SneakyThrows
+    private CompletableFuture<Void> asyncLoadNextBucketSnapshotEntry(Bucket bucket, boolean isRebuild) {
+        if (log.isDebugEnabled()) {
+            log.debug("[{}] Load next bucket snapshot data, bucket: {}", dispatcher.getName(), bucket);
+        }
+        if (bucket == null) {
+            return CompletableFuture.completedFuture(null);
+        }
+
+        final CompletableFuture<Long> createFuture = bucket.snapshotCreateFuture;
+        if (createFuture != null) {
+            // Wait bucket snapshot create finish
+            createFuture.get();

Review Comment:
   We don't suggest using the blocking calls in the async method.



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/BucketDelayedDeliveryTracker.java:
##########
@@ -0,0 +1,565 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static org.apache.bookkeeper.mledger.util.Futures.executeWithRetry;
+import com.google.common.collect.HashBasedTable;
+import com.google.common.collect.Range;
+import com.google.common.collect.RangeMap;
+import com.google.common.collect.Table;
+import com.google.common.collect.TreeRangeMap;
+import com.google.protobuf.ByteString;
+import io.netty.util.Timeout;
+import io.netty.util.Timer;
+import java.time.Clock;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.concurrent.CompletableFuture;
+import javax.annotation.concurrent.ThreadSafe;
+import lombok.SneakyThrows;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.bookkeeper.mledger.ManagedCursor;
+import org.apache.bookkeeper.mledger.ManagedLedgerException;
+import org.apache.bookkeeper.mledger.impl.PositionImpl;
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.lang.StringUtils;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.DelayedIndex;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotMetadata;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegment;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+import org.apache.pulsar.broker.service.persistent.PersistentDispatcherMultipleConsumers;
+import org.apache.pulsar.common.util.collections.TripleLongPriorityQueue;
+
+@Slf4j
+@ThreadSafe
+public class BucketDelayedDeliveryTracker extends InMemoryDelayedDeliveryTracker {
+
+    public static final String DELAYED_BUCKET_KEY_PREFIX = "#pulsar.internal.delayed.bucket";
+
+    public static final String DELIMITER = "_";
+
+    private final long minIndexCountPerBucket;
+
+    private final long timeStepPerBucketSnapshotSegment;
+
+    private final int maxNumBuckets;
+
+    private final ManagedCursor cursor;
+
+    public final BucketSnapshotStorage bucketSnapshotStorage;
+
+    private long numberDelayedMessages;
+
+    private final Bucket lastMutableBucket;
+
+    private final TripleLongPriorityQueue sharedBucketPriorityQueue;
+
+    private final RangeMap<Long, Bucket> immutableBuckets;
+
+    private final Table<Long, Long, Bucket> snapshotSegmentLastIndexTable;
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 long fixedDelayDetectionLookahead,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        this(dispatcher, timer, tickTimeMillis, Clock.systemUTC(), isDelayedDeliveryDeliverAtTimeStrict,
+                fixedDelayDetectionLookahead,
+                bucketSnapshotStorage, minIndexCountPerBucket, timeStepPerBucketSnapshotSegment, maxNumBuckets);
+    }
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis, Clock clock,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 long fixedDelayDetectionLookahead,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        super(dispatcher, timer, tickTimeMillis, clock, isDelayedDeliveryDeliverAtTimeStrict,
+                fixedDelayDetectionLookahead);
+        this.minIndexCountPerBucket = minIndexCountPerBucket;
+        this.timeStepPerBucketSnapshotSegment = timeStepPerBucketSnapshotSegment;
+        this.maxNumBuckets = maxNumBuckets;
+        this.cursor = dispatcher.getCursor();
+        this.sharedBucketPriorityQueue = new TripleLongPriorityQueue();
+        this.immutableBuckets = TreeRangeMap.create();
+        this.snapshotSegmentLastIndexTable = HashBasedTable.create();
+
+        this.bucketSnapshotStorage = bucketSnapshotStorage;
+
+        numberDelayedMessages = 0L;
+
+        this.lastMutableBucket = new Bucket(-1L, -1L, new HashMap<>());
+    }
+
+    private void moveScheduledMessageToSharedQueue(long cutoffTime) {
+        TripleLongPriorityQueue priorityQueue = getPriorityQueue();
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (timestamp > cutoffTime) {
+                break;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+            sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+
+            priorityQueue.pop();
+        }
+    }
+
+    @Override
+    public void run(Timeout timeout) throws Exception {
+        synchronized (this) {
+            moveScheduledMessageToSharedQueue(getCutoffTime());
+        }
+        super.run(timeout);
+    }
+
+    private Optional<Bucket> findBucket(long ledgerId) {
+        if (immutableBuckets.asMapOfRanges().isEmpty()) {
+            return Optional.empty();
+        }
+
+        Range<Long> span = immutableBuckets.span();
+        if (!span.contains(ledgerId)) {
+            return Optional.empty();
+        }
+        return Optional.ofNullable(immutableBuckets.get(ledgerId));
+    }
+
+    private Long getBucketIdByBucketKey(String bucketKey) {
+        String bucketIdStr = cursor.getCursorProperties().get(bucketKey);
+        if (StringUtils.isBlank(bucketIdStr)) {
+            return null;
+        }
+        return Long.valueOf(bucketIdStr);
+    }
+
+    private Bucket createImmutableBucket(long startLedgerId, long endLedgerId) {
+        Bucket newBucket = new Bucket(startLedgerId, endLedgerId, new HashMap<>());
+        immutableBuckets.put(Range.closed(startLedgerId, endLedgerId), newBucket);
+        return newBucket;
+    }
+
+    private CompletableFuture<Long> asyncSaveBucketSnapshot(
+            final String bucketKey, SnapshotMetadata snapshotMetadata,
+            List<SnapshotSegment> bucketSnapshotSegments) {
+        Long bucketId = getBucketIdByBucketKey(bucketKey);
+        checkArgument(bucketId == null);
+
+        return bucketSnapshotStorage.createBucketSnapshot(snapshotMetadata, bucketSnapshotSegments)
+                .thenCompose(newBucketId -> putBucketKeyId(bucketKey, newBucketId));
+    }
+
+    private CompletableFuture<Long> putBucketKeyId(String bucketKey, Long bucketId) {
+        Objects.requireNonNull(bucketId);
+        return executeWithRetry(() -> cursor.putCursorProperty(bucketKey, String.valueOf(bucketId)),
+                ManagedLedgerException.BadVersionException.class).thenApply(__ -> bucketId);
+    }
+
+    private CompletableFuture<Long> asyncCreateBucketSnapshot() {
+        TripleLongPriorityQueue priorityQueue = super.getPriorityQueue();
+        if (priorityQueue.isEmpty()) {
+            return CompletableFuture.completedFuture(null);
+        }
+        long numMessages = 0;
+
+        final long startLedgerId = lastMutableBucket.startLedgerId;
+        final long endLedgerId = lastMutableBucket.endLedgerId;
+
+        List<SnapshotSegment> bucketSnapshotSegments = new ArrayList<>();
+        List<SnapshotSegmentMetadata> segmentMetadataList = new ArrayList<>();
+        Map<Long, BitSet> bitMap = new HashMap<>();
+        SnapshotSegment.Builder snapshotSegmentBuilder = SnapshotSegment.newBuilder();
+        SnapshotSegmentMetadata.Builder segmentMetadataBuilder = SnapshotSegmentMetadata.newBuilder();
+
+        long currentTimestampUpperLimit = 0;
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (currentTimestampUpperLimit == 0) {
+                currentTimestampUpperLimit = timestamp + timeStepPerBucketSnapshotSegment - 1;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+
+            checkArgument(ledgerId >= startLedgerId && ledgerId <= endLedgerId);

Review Comment:
   I see many `checkArgument` methods in the several async methods, it has a risk to throw the exception and we may forget to handle it.



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/BucketDelayedDeliveryTracker.java:
##########
@@ -0,0 +1,628 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static org.apache.bookkeeper.mledger.util.Futures.executeWithRetry;
+import com.google.common.collect.HashBasedTable;
+import com.google.common.collect.Range;
+import com.google.common.collect.RangeMap;
+import com.google.common.collect.Table;
+import com.google.common.collect.TreeRangeMap;
+import com.google.protobuf.ByteString;
+import io.netty.util.Timeout;
+import io.netty.util.Timer;
+import java.time.Clock;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.concurrent.CompletableFuture;
+import javax.annotation.concurrent.ThreadSafe;
+import lombok.SneakyThrows;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.bookkeeper.mledger.ManagedCursor;
+import org.apache.bookkeeper.mledger.ManagedLedgerException;
+import org.apache.bookkeeper.mledger.impl.PositionImpl;
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.lang.StringUtils;
+import org.apache.commons.lang3.mutable.MutableLong;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.DelayedIndex;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotMetadata;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegment;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+import org.apache.pulsar.broker.service.persistent.PersistentDispatcherMultipleConsumers;
+import org.apache.pulsar.common.util.FutureUtil;
+import org.apache.pulsar.common.util.collections.TripleLongPriorityQueue;
+
+@Slf4j
+@ThreadSafe
+public class BucketDelayedDeliveryTracker extends InMemoryDelayedDeliveryTracker {
+
+    public static final String DELAYED_BUCKET_KEY_PREFIX = "#pulsar.internal.delayed.bucket";
+
+    public static final String DELIMITER = "_";
+
+    private final long minIndexCountPerBucket;
+
+    private final long timeStepPerBucketSnapshotSegment;
+
+    private final int maxNumBuckets;
+
+    private final ManagedCursor cursor;
+
+    public final BucketSnapshotStorage bucketSnapshotStorage;
+
+    private long numberDelayedMessages;
+
+    private final Bucket lastMutableBucket;
+
+    private final TripleLongPriorityQueue sharedBucketPriorityQueue;
+
+    private final RangeMap<Long, Bucket> immutableBuckets;
+
+    private final Table<Long, Long, Bucket> snapshotSegmentLastIndexTable;
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        this(dispatcher, timer, tickTimeMillis, Clock.systemUTC(), isDelayedDeliveryDeliverAtTimeStrict,
+                bucketSnapshotStorage, minIndexCountPerBucket, timeStepPerBucketSnapshotSegment, maxNumBuckets);
+    }
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis, Clock clock,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        super(dispatcher, timer, tickTimeMillis, clock, isDelayedDeliveryDeliverAtTimeStrict);
+        this.minIndexCountPerBucket = minIndexCountPerBucket;
+        this.timeStepPerBucketSnapshotSegment = timeStepPerBucketSnapshotSegment;
+        this.maxNumBuckets = maxNumBuckets;
+        this.cursor = dispatcher.getCursor();
+        this.sharedBucketPriorityQueue = new TripleLongPriorityQueue();
+        this.immutableBuckets = TreeRangeMap.create();
+        this.snapshotSegmentLastIndexTable = HashBasedTable.create();
+
+        this.bucketSnapshotStorage = bucketSnapshotStorage;
+
+        numberDelayedMessages = recoverBucketSnapshot();
+
+        this.lastMutableBucket = new Bucket(-1L, -1L, new HashMap<>());
+    }
+
+    @SneakyThrows
+    private long recoverBucketSnapshot() {
+        List<CompletableFuture<Void>> completableFutures = new ArrayList<>();
+        this.cursor.getCursorProperties().keySet().forEach(key -> {
+            if (key.startsWith(DELAYED_BUCKET_KEY_PREFIX)) {
+                String[] keys = key.split(DELIMITER);
+                checkArgument(keys.length == 3);
+                Bucket bucket = createImmutableBucket(Long.parseLong(keys[1]), Long.parseLong(keys[2]));
+                completableFutures.add(asyncLoadNextBucketSnapshotEntry(bucket, true));
+            }
+        });
+
+        if (completableFutures.isEmpty()) {
+            return 0;
+        }
+
+        FutureUtil.waitForAll(completableFutures).get();

Review Comment:
   Why can't we make it to be async?



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/BucketDelayedDeliveryTracker.java:
##########
@@ -0,0 +1,628 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static org.apache.bookkeeper.mledger.util.Futures.executeWithRetry;
+import com.google.common.collect.HashBasedTable;
+import com.google.common.collect.Range;
+import com.google.common.collect.RangeMap;
+import com.google.common.collect.Table;
+import com.google.common.collect.TreeRangeMap;
+import com.google.protobuf.ByteString;
+import io.netty.util.Timeout;
+import io.netty.util.Timer;
+import java.time.Clock;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.concurrent.CompletableFuture;
+import javax.annotation.concurrent.ThreadSafe;
+import lombok.SneakyThrows;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.bookkeeper.mledger.ManagedCursor;
+import org.apache.bookkeeper.mledger.ManagedLedgerException;
+import org.apache.bookkeeper.mledger.impl.PositionImpl;
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.lang.StringUtils;
+import org.apache.commons.lang3.mutable.MutableLong;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.DelayedIndex;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotMetadata;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegment;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+import org.apache.pulsar.broker.service.persistent.PersistentDispatcherMultipleConsumers;
+import org.apache.pulsar.common.util.FutureUtil;
+import org.apache.pulsar.common.util.collections.TripleLongPriorityQueue;
+
+@Slf4j
+@ThreadSafe
+public class BucketDelayedDeliveryTracker extends InMemoryDelayedDeliveryTracker {
+
+    public static final String DELAYED_BUCKET_KEY_PREFIX = "#pulsar.internal.delayed.bucket";
+
+    public static final String DELIMITER = "_";
+
+    private final long minIndexCountPerBucket;
+
+    private final long timeStepPerBucketSnapshotSegment;
+
+    private final int maxNumBuckets;
+
+    private final ManagedCursor cursor;
+
+    public final BucketSnapshotStorage bucketSnapshotStorage;
+
+    private long numberDelayedMessages;
+
+    private final Bucket lastMutableBucket;
+
+    private final TripleLongPriorityQueue sharedBucketPriorityQueue;
+
+    private final RangeMap<Long, Bucket> immutableBuckets;
+
+    private final Table<Long, Long, Bucket> snapshotSegmentLastIndexTable;
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        this(dispatcher, timer, tickTimeMillis, Clock.systemUTC(), isDelayedDeliveryDeliverAtTimeStrict,
+                bucketSnapshotStorage, minIndexCountPerBucket, timeStepPerBucketSnapshotSegment, maxNumBuckets);
+    }
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis, Clock clock,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        super(dispatcher, timer, tickTimeMillis, clock, isDelayedDeliveryDeliverAtTimeStrict);
+        this.minIndexCountPerBucket = minIndexCountPerBucket;
+        this.timeStepPerBucketSnapshotSegment = timeStepPerBucketSnapshotSegment;
+        this.maxNumBuckets = maxNumBuckets;
+        this.cursor = dispatcher.getCursor();
+        this.sharedBucketPriorityQueue = new TripleLongPriorityQueue();
+        this.immutableBuckets = TreeRangeMap.create();
+        this.snapshotSegmentLastIndexTable = HashBasedTable.create();
+
+        this.bucketSnapshotStorage = bucketSnapshotStorage;
+
+        numberDelayedMessages = recoverBucketSnapshot();
+
+        this.lastMutableBucket = new Bucket(-1L, -1L, new HashMap<>());
+    }
+
+    @SneakyThrows
+    private long recoverBucketSnapshot() {
+        List<CompletableFuture<Void>> completableFutures = new ArrayList<>();
+        this.cursor.getCursorProperties().keySet().forEach(key -> {
+            if (key.startsWith(DELAYED_BUCKET_KEY_PREFIX)) {
+                String[] keys = key.split(DELIMITER);
+                checkArgument(keys.length == 3);
+                Bucket bucket = createImmutableBucket(Long.parseLong(keys[1]), Long.parseLong(keys[2]));
+                completableFutures.add(asyncLoadNextBucketSnapshotEntry(bucket, true));
+            }
+        });
+
+        if (completableFutures.isEmpty()) {
+            return 0;
+        }
+
+        FutureUtil.waitForAll(completableFutures).get();
+
+        MutableLong numberDelayedMessages = new MutableLong(0);
+        immutableBuckets.asMapOfRanges().values().forEach(bucket -> {
+            numberDelayedMessages.add(bucket.numberBucketDelayedMessages);
+        });
+
+        log.info("[{}] Recover delayed message index bucket snapshot finish, buckets: {}, numberDelayedMessages: {}",
+                dispatcher.getName(), immutableBuckets.asMapOfRanges().size(), numberDelayedMessages.getValue());
+
+        return numberDelayedMessages.getValue();
+    }
+
+    private void moveScheduledMessageToSharedQueue(long cutoffTime) {
+        TripleLongPriorityQueue priorityQueue = getPriorityQueue();
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (timestamp > cutoffTime) {
+                break;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+            sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+
+            priorityQueue.pop();
+        }
+    }
+
+    @Override
+    public void run(Timeout timeout) throws Exception {
+        synchronized (this) {
+            moveScheduledMessageToSharedQueue(getCutoffTime());
+        }
+        super.run(timeout);
+    }
+
+    private Optional<Bucket> findBucket(long ledgerId) {
+        if (immutableBuckets.asMapOfRanges().isEmpty()) {
+            return Optional.empty();
+        }
+
+        Range<Long> span = immutableBuckets.span();
+        if (!span.contains(ledgerId)) {
+            return Optional.empty();
+        }
+        return Optional.ofNullable(immutableBuckets.get(ledgerId));
+    }
+
+    private Long getBucketIdByBucketKey(String bucketKey) {
+        String bucketIdStr = cursor.getCursorProperties().get(bucketKey);
+        if (StringUtils.isBlank(bucketIdStr)) {
+            return null;
+        }
+        return Long.valueOf(bucketIdStr);
+    }
+
+    private Bucket createImmutableBucket(long startLedgerId, long endLedgerId) {
+        Bucket newBucket = new Bucket(startLedgerId, endLedgerId, new HashMap<>());
+        immutableBuckets.put(Range.closed(startLedgerId, endLedgerId), newBucket);
+        return newBucket;
+    }
+
+    private CompletableFuture<Long> asyncSaveBucketSnapshot(
+            final String bucketKey, SnapshotMetadata snapshotMetadata,
+            List<SnapshotSegment> bucketSnapshotSegments) {
+        Long bucketId = getBucketIdByBucketKey(bucketKey);
+        checkArgument(bucketId == null);
+
+        return bucketSnapshotStorage.createBucketSnapshot(snapshotMetadata, bucketSnapshotSegments)
+                .thenCompose(newBucketId -> putBucketKeyId(bucketKey, newBucketId));
+    }
+
+    private CompletableFuture<Long> putBucketKeyId(String bucketKey, Long bucketId) {
+        Objects.requireNonNull(bucketId);
+        return executeWithRetry(() -> cursor.putCursorProperty(bucketKey, String.valueOf(bucketId)),
+                ManagedLedgerException.BadVersionException.class).thenApply(__ -> bucketId);
+    }
+
+    private CompletableFuture<Long> asyncCreateBucketSnapshot() {
+        TripleLongPriorityQueue priorityQueue = super.getPriorityQueue();
+        if (priorityQueue.isEmpty()) {
+            return CompletableFuture.completedFuture(null);
+        }
+        long numMessages = 0;
+
+        final long startLedgerId = lastMutableBucket.startLedgerId;
+        final long endLedgerId = lastMutableBucket.endLedgerId;
+
+        List<SnapshotSegment> bucketSnapshotSegments = new ArrayList<>();
+        List<SnapshotSegmentMetadata> segmentMetadataList = new ArrayList<>();
+        Map<Long, BitSet> bitMap = new HashMap<>();
+        SnapshotSegment.Builder snapshotSegmentBuilder = SnapshotSegment.newBuilder();
+        SnapshotSegmentMetadata.Builder segmentMetadataBuilder = SnapshotSegmentMetadata.newBuilder();
+
+        long currentTimestampUpperLimit = 0;
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (currentTimestampUpperLimit == 0) {
+                currentTimestampUpperLimit = timestamp + timeStepPerBucketSnapshotSegment - 1;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+
+            checkArgument(ledgerId >= startLedgerId && ledgerId <= endLedgerId);
+
+            // Move first segment of bucket snapshot to sharedBucketPriorityQueue
+            if (segmentMetadataList.size() == 0) {
+                sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+            }
+
+            priorityQueue.pop();
+            numMessages++;
+
+            DelayedIndex delayedIndex = DelayedIndex.newBuilder()
+                    .setTimestamp(timestamp)
+                    .setLedgerId(ledgerId)
+                    .setEntryId(entryId).build();
+
+            if (entryId <= Integer.MAX_VALUE) {
+                bitMap.compute(ledgerId, (k, v) -> new BitSet()).set((int) entryId);

Review Comment:
   `computeIfAbsent`?



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/BucketDelayedDeliveryTracker.java:
##########
@@ -0,0 +1,565 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static org.apache.bookkeeper.mledger.util.Futures.executeWithRetry;
+import com.google.common.collect.HashBasedTable;
+import com.google.common.collect.Range;
+import com.google.common.collect.RangeMap;
+import com.google.common.collect.Table;
+import com.google.common.collect.TreeRangeMap;
+import com.google.protobuf.ByteString;
+import io.netty.util.Timeout;
+import io.netty.util.Timer;
+import java.time.Clock;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.concurrent.CompletableFuture;
+import javax.annotation.concurrent.ThreadSafe;
+import lombok.SneakyThrows;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.bookkeeper.mledger.ManagedCursor;
+import org.apache.bookkeeper.mledger.ManagedLedgerException;
+import org.apache.bookkeeper.mledger.impl.PositionImpl;
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.lang.StringUtils;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.DelayedIndex;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotMetadata;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegment;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+import org.apache.pulsar.broker.service.persistent.PersistentDispatcherMultipleConsumers;
+import org.apache.pulsar.common.util.collections.TripleLongPriorityQueue;
+
+@Slf4j
+@ThreadSafe
+public class BucketDelayedDeliveryTracker extends InMemoryDelayedDeliveryTracker {
+
+    public static final String DELAYED_BUCKET_KEY_PREFIX = "#pulsar.internal.delayed.bucket";
+
+    public static final String DELIMITER = "_";
+
+    private final long minIndexCountPerBucket;
+
+    private final long timeStepPerBucketSnapshotSegment;
+
+    private final int maxNumBuckets;
+
+    private final ManagedCursor cursor;
+
+    public final BucketSnapshotStorage bucketSnapshotStorage;
+
+    private long numberDelayedMessages;
+
+    private final Bucket lastMutableBucket;
+
+    private final TripleLongPriorityQueue sharedBucketPriorityQueue;
+
+    private final RangeMap<Long, Bucket> immutableBuckets;
+
+    private final Table<Long, Long, Bucket> snapshotSegmentLastIndexTable;
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 long fixedDelayDetectionLookahead,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        this(dispatcher, timer, tickTimeMillis, Clock.systemUTC(), isDelayedDeliveryDeliverAtTimeStrict,
+                fixedDelayDetectionLookahead,
+                bucketSnapshotStorage, minIndexCountPerBucket, timeStepPerBucketSnapshotSegment, maxNumBuckets);
+    }
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis, Clock clock,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 long fixedDelayDetectionLookahead,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        super(dispatcher, timer, tickTimeMillis, clock, isDelayedDeliveryDeliverAtTimeStrict,
+                fixedDelayDetectionLookahead);
+        this.minIndexCountPerBucket = minIndexCountPerBucket;
+        this.timeStepPerBucketSnapshotSegment = timeStepPerBucketSnapshotSegment;
+        this.maxNumBuckets = maxNumBuckets;
+        this.cursor = dispatcher.getCursor();
+        this.sharedBucketPriorityQueue = new TripleLongPriorityQueue();
+        this.immutableBuckets = TreeRangeMap.create();
+        this.snapshotSegmentLastIndexTable = HashBasedTable.create();
+
+        this.bucketSnapshotStorage = bucketSnapshotStorage;
+
+        numberDelayedMessages = 0L;
+
+        this.lastMutableBucket = new Bucket(-1L, -1L, new HashMap<>());
+    }
+
+    private void moveScheduledMessageToSharedQueue(long cutoffTime) {
+        TripleLongPriorityQueue priorityQueue = getPriorityQueue();
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (timestamp > cutoffTime) {
+                break;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+            sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+
+            priorityQueue.pop();
+        }
+    }
+
+    @Override
+    public void run(Timeout timeout) throws Exception {
+        synchronized (this) {
+            moveScheduledMessageToSharedQueue(getCutoffTime());
+        }
+        super.run(timeout);
+    }
+
+    private Optional<Bucket> findBucket(long ledgerId) {
+        if (immutableBuckets.asMapOfRanges().isEmpty()) {
+            return Optional.empty();
+        }
+
+        Range<Long> span = immutableBuckets.span();
+        if (!span.contains(ledgerId)) {
+            return Optional.empty();
+        }
+        return Optional.ofNullable(immutableBuckets.get(ledgerId));
+    }
+
+    private Long getBucketIdByBucketKey(String bucketKey) {
+        String bucketIdStr = cursor.getCursorProperties().get(bucketKey);
+        if (StringUtils.isBlank(bucketIdStr)) {
+            return null;
+        }
+        return Long.valueOf(bucketIdStr);
+    }
+
+    private Bucket createImmutableBucket(long startLedgerId, long endLedgerId) {
+        Bucket newBucket = new Bucket(startLedgerId, endLedgerId, new HashMap<>());
+        immutableBuckets.put(Range.closed(startLedgerId, endLedgerId), newBucket);
+        return newBucket;
+    }
+
+    private CompletableFuture<Long> asyncSaveBucketSnapshot(
+            final String bucketKey, SnapshotMetadata snapshotMetadata,
+            List<SnapshotSegment> bucketSnapshotSegments) {
+        Long bucketId = getBucketIdByBucketKey(bucketKey);
+        checkArgument(bucketId == null);
+
+        return bucketSnapshotStorage.createBucketSnapshot(snapshotMetadata, bucketSnapshotSegments)
+                .thenCompose(newBucketId -> putBucketKeyId(bucketKey, newBucketId));
+    }
+
+    private CompletableFuture<Long> putBucketKeyId(String bucketKey, Long bucketId) {
+        Objects.requireNonNull(bucketId);
+        return executeWithRetry(() -> cursor.putCursorProperty(bucketKey, String.valueOf(bucketId)),
+                ManagedLedgerException.BadVersionException.class).thenApply(__ -> bucketId);
+    }
+
+    private CompletableFuture<Long> asyncCreateBucketSnapshot() {
+        TripleLongPriorityQueue priorityQueue = super.getPriorityQueue();
+        if (priorityQueue.isEmpty()) {
+            return CompletableFuture.completedFuture(null);
+        }
+        long numMessages = 0;
+
+        final long startLedgerId = lastMutableBucket.startLedgerId;
+        final long endLedgerId = lastMutableBucket.endLedgerId;
+
+        List<SnapshotSegment> bucketSnapshotSegments = new ArrayList<>();
+        List<SnapshotSegmentMetadata> segmentMetadataList = new ArrayList<>();
+        Map<Long, BitSet> bitMap = new HashMap<>();
+        SnapshotSegment.Builder snapshotSegmentBuilder = SnapshotSegment.newBuilder();
+        SnapshotSegmentMetadata.Builder segmentMetadataBuilder = SnapshotSegmentMetadata.newBuilder();
+
+        long currentTimestampUpperLimit = 0;
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (currentTimestampUpperLimit == 0) {
+                currentTimestampUpperLimit = timestamp + timeStepPerBucketSnapshotSegment - 1;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+
+            checkArgument(ledgerId >= startLedgerId && ledgerId <= endLedgerId);
+
+            // Move first segment of bucket snapshot to sharedBucketPriorityQueue
+            if (segmentMetadataList.size() == 0) {
+                sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+            }
+
+            priorityQueue.pop();
+            numMessages++;
+
+            DelayedIndex delayedIndex = DelayedIndex.newBuilder()
+                    .setTimestamp(timestamp)
+                    .setLedgerId(ledgerId)
+                    .setEntryId(entryId).build();
+
+            if (entryId <= Integer.MAX_VALUE) {
+                bitMap.compute(ledgerId, (k, v) -> new BitSet()).set((int) entryId);
+            }
+
+            snapshotSegmentBuilder.addIndexes(delayedIndex);
+
+            if (priorityQueue.isEmpty() || priorityQueue.peekN1() > currentTimestampUpperLimit) {
+                segmentMetadataBuilder.setMaxScheduleTimestamp(timestamp);
+                currentTimestampUpperLimit = 0;
+
+                Iterator<Map.Entry<Long, BitSet>> iterator = bitMap.entrySet().iterator();
+                while (iterator.hasNext()) {
+                    Map.Entry<Long, BitSet> entry = iterator.next();
+                    ByteString byteString = ByteString.copyFrom(entry.getValue().toByteArray());
+                    segmentMetadataBuilder.putDelayedIndexBitMap(entry.getKey(), byteString);
+                    iterator.remove();
+                }
+
+                segmentMetadataList.add(segmentMetadataBuilder.build());
+                segmentMetadataBuilder.clear();
+
+                bucketSnapshotSegments.add(snapshotSegmentBuilder.build());
+                snapshotSegmentBuilder.clear();
+            }
+        }
+
+        SnapshotMetadata bucketSnapshotMetadata = SnapshotMetadata.newBuilder()
+                .addAllMetadataList(segmentMetadataList)

Review Comment:
   Is there any chance it will be empty?



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/BucketDelayedDeliveryTracker.java:
##########
@@ -0,0 +1,628 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static org.apache.bookkeeper.mledger.util.Futures.executeWithRetry;
+import com.google.common.collect.HashBasedTable;
+import com.google.common.collect.Range;
+import com.google.common.collect.RangeMap;
+import com.google.common.collect.Table;
+import com.google.common.collect.TreeRangeMap;
+import com.google.protobuf.ByteString;
+import io.netty.util.Timeout;
+import io.netty.util.Timer;
+import java.time.Clock;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.concurrent.CompletableFuture;
+import javax.annotation.concurrent.ThreadSafe;
+import lombok.SneakyThrows;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.bookkeeper.mledger.ManagedCursor;
+import org.apache.bookkeeper.mledger.ManagedLedgerException;
+import org.apache.bookkeeper.mledger.impl.PositionImpl;
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.lang.StringUtils;
+import org.apache.commons.lang3.mutable.MutableLong;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.DelayedIndex;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotMetadata;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegment;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+import org.apache.pulsar.broker.service.persistent.PersistentDispatcherMultipleConsumers;
+import org.apache.pulsar.common.util.FutureUtil;
+import org.apache.pulsar.common.util.collections.TripleLongPriorityQueue;
+
+@Slf4j
+@ThreadSafe
+public class BucketDelayedDeliveryTracker extends InMemoryDelayedDeliveryTracker {
+
+    public static final String DELAYED_BUCKET_KEY_PREFIX = "#pulsar.internal.delayed.bucket";
+
+    public static final String DELIMITER = "_";
+
+    private final long minIndexCountPerBucket;
+
+    private final long timeStepPerBucketSnapshotSegment;
+
+    private final int maxNumBuckets;
+
+    private final ManagedCursor cursor;
+
+    public final BucketSnapshotStorage bucketSnapshotStorage;
+
+    private long numberDelayedMessages;
+
+    private final Bucket lastMutableBucket;
+
+    private final TripleLongPriorityQueue sharedBucketPriorityQueue;
+
+    private final RangeMap<Long, Bucket> immutableBuckets;
+
+    private final Table<Long, Long, Bucket> snapshotSegmentLastIndexTable;
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        this(dispatcher, timer, tickTimeMillis, Clock.systemUTC(), isDelayedDeliveryDeliverAtTimeStrict,
+                bucketSnapshotStorage, minIndexCountPerBucket, timeStepPerBucketSnapshotSegment, maxNumBuckets);
+    }
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis, Clock clock,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        super(dispatcher, timer, tickTimeMillis, clock, isDelayedDeliveryDeliverAtTimeStrict);
+        this.minIndexCountPerBucket = minIndexCountPerBucket;
+        this.timeStepPerBucketSnapshotSegment = timeStepPerBucketSnapshotSegment;
+        this.maxNumBuckets = maxNumBuckets;
+        this.cursor = dispatcher.getCursor();
+        this.sharedBucketPriorityQueue = new TripleLongPriorityQueue();
+        this.immutableBuckets = TreeRangeMap.create();
+        this.snapshotSegmentLastIndexTable = HashBasedTable.create();
+
+        this.bucketSnapshotStorage = bucketSnapshotStorage;
+
+        numberDelayedMessages = recoverBucketSnapshot();

Review Comment:
   If `recoverBucketSnapshot` throws an exception, the `lastMutableBucket` will be null.



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/InMemoryDelayedDeliveryTracker.java:
##########
@@ -274,22 +279,29 @@ public void run(Timeout timeout) throws Exception {
 
     @Override
     public void close() {
-        priorityQueue.close();
         if (timeout != null) {
             timeout.cancel();
         }
+        priorityQueue.close();

Review Comment:
   Why move it?



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/BucketDelayedDeliveryTracker.java:
##########
@@ -0,0 +1,565 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static org.apache.bookkeeper.mledger.util.Futures.executeWithRetry;
+import com.google.common.collect.HashBasedTable;
+import com.google.common.collect.Range;
+import com.google.common.collect.RangeMap;
+import com.google.common.collect.Table;
+import com.google.common.collect.TreeRangeMap;
+import com.google.protobuf.ByteString;
+import io.netty.util.Timeout;
+import io.netty.util.Timer;
+import java.time.Clock;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.concurrent.CompletableFuture;
+import javax.annotation.concurrent.ThreadSafe;
+import lombok.SneakyThrows;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.bookkeeper.mledger.ManagedCursor;
+import org.apache.bookkeeper.mledger.ManagedLedgerException;
+import org.apache.bookkeeper.mledger.impl.PositionImpl;
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.lang.StringUtils;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.DelayedIndex;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotMetadata;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegment;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+import org.apache.pulsar.broker.service.persistent.PersistentDispatcherMultipleConsumers;
+import org.apache.pulsar.common.util.collections.TripleLongPriorityQueue;
+
+@Slf4j
+@ThreadSafe
+public class BucketDelayedDeliveryTracker extends InMemoryDelayedDeliveryTracker {
+
+    public static final String DELAYED_BUCKET_KEY_PREFIX = "#pulsar.internal.delayed.bucket";
+
+    public static final String DELIMITER = "_";
+
+    private final long minIndexCountPerBucket;
+
+    private final long timeStepPerBucketSnapshotSegment;
+
+    private final int maxNumBuckets;
+
+    private final ManagedCursor cursor;
+
+    public final BucketSnapshotStorage bucketSnapshotStorage;
+
+    private long numberDelayedMessages;
+
+    private final Bucket lastMutableBucket;
+
+    private final TripleLongPriorityQueue sharedBucketPriorityQueue;
+
+    private final RangeMap<Long, Bucket> immutableBuckets;
+
+    private final Table<Long, Long, Bucket> snapshotSegmentLastIndexTable;
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 long fixedDelayDetectionLookahead,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        this(dispatcher, timer, tickTimeMillis, Clock.systemUTC(), isDelayedDeliveryDeliverAtTimeStrict,
+                fixedDelayDetectionLookahead,
+                bucketSnapshotStorage, minIndexCountPerBucket, timeStepPerBucketSnapshotSegment, maxNumBuckets);
+    }
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis, Clock clock,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 long fixedDelayDetectionLookahead,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        super(dispatcher, timer, tickTimeMillis, clock, isDelayedDeliveryDeliverAtTimeStrict,
+                fixedDelayDetectionLookahead);
+        this.minIndexCountPerBucket = minIndexCountPerBucket;
+        this.timeStepPerBucketSnapshotSegment = timeStepPerBucketSnapshotSegment;
+        this.maxNumBuckets = maxNumBuckets;
+        this.cursor = dispatcher.getCursor();
+        this.sharedBucketPriorityQueue = new TripleLongPriorityQueue();
+        this.immutableBuckets = TreeRangeMap.create();
+        this.snapshotSegmentLastIndexTable = HashBasedTable.create();
+
+        this.bucketSnapshotStorage = bucketSnapshotStorage;
+
+        numberDelayedMessages = 0L;
+
+        this.lastMutableBucket = new Bucket(-1L, -1L, new HashMap<>());
+    }
+
+    private void moveScheduledMessageToSharedQueue(long cutoffTime) {
+        TripleLongPriorityQueue priorityQueue = getPriorityQueue();
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (timestamp > cutoffTime) {
+                break;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+            sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+
+            priorityQueue.pop();
+        }
+    }
+
+    @Override
+    public void run(Timeout timeout) throws Exception {
+        synchronized (this) {
+            moveScheduledMessageToSharedQueue(getCutoffTime());
+        }
+        super.run(timeout);
+    }
+
+    private Optional<Bucket> findBucket(long ledgerId) {
+        if (immutableBuckets.asMapOfRanges().isEmpty()) {
+            return Optional.empty();
+        }
+
+        Range<Long> span = immutableBuckets.span();
+        if (!span.contains(ledgerId)) {
+            return Optional.empty();
+        }
+        return Optional.ofNullable(immutableBuckets.get(ledgerId));
+    }
+
+    private Long getBucketIdByBucketKey(String bucketKey) {
+        String bucketIdStr = cursor.getCursorProperties().get(bucketKey);
+        if (StringUtils.isBlank(bucketIdStr)) {
+            return null;
+        }
+        return Long.valueOf(bucketIdStr);
+    }
+
+    private Bucket createImmutableBucket(long startLedgerId, long endLedgerId) {
+        Bucket newBucket = new Bucket(startLedgerId, endLedgerId, new HashMap<>());
+        immutableBuckets.put(Range.closed(startLedgerId, endLedgerId), newBucket);
+        return newBucket;
+    }
+
+    private CompletableFuture<Long> asyncSaveBucketSnapshot(
+            final String bucketKey, SnapshotMetadata snapshotMetadata,
+            List<SnapshotSegment> bucketSnapshotSegments) {
+        Long bucketId = getBucketIdByBucketKey(bucketKey);
+        checkArgument(bucketId == null);
+
+        return bucketSnapshotStorage.createBucketSnapshot(snapshotMetadata, bucketSnapshotSegments)
+                .thenCompose(newBucketId -> putBucketKeyId(bucketKey, newBucketId));
+    }
+
+    private CompletableFuture<Long> putBucketKeyId(String bucketKey, Long bucketId) {
+        Objects.requireNonNull(bucketId);
+        return executeWithRetry(() -> cursor.putCursorProperty(bucketKey, String.valueOf(bucketId)),
+                ManagedLedgerException.BadVersionException.class).thenApply(__ -> bucketId);
+    }
+
+    private CompletableFuture<Long> asyncCreateBucketSnapshot() {
+        TripleLongPriorityQueue priorityQueue = super.getPriorityQueue();
+        if (priorityQueue.isEmpty()) {
+            return CompletableFuture.completedFuture(null);
+        }
+        long numMessages = 0;
+
+        final long startLedgerId = lastMutableBucket.startLedgerId;
+        final long endLedgerId = lastMutableBucket.endLedgerId;
+
+        List<SnapshotSegment> bucketSnapshotSegments = new ArrayList<>();
+        List<SnapshotSegmentMetadata> segmentMetadataList = new ArrayList<>();
+        Map<Long, BitSet> bitMap = new HashMap<>();
+        SnapshotSegment.Builder snapshotSegmentBuilder = SnapshotSegment.newBuilder();
+        SnapshotSegmentMetadata.Builder segmentMetadataBuilder = SnapshotSegmentMetadata.newBuilder();
+
+        long currentTimestampUpperLimit = 0;
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (currentTimestampUpperLimit == 0) {
+                currentTimestampUpperLimit = timestamp + timeStepPerBucketSnapshotSegment - 1;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+
+            checkArgument(ledgerId >= startLedgerId && ledgerId <= endLedgerId);
+
+            // Move first segment of bucket snapshot to sharedBucketPriorityQueue
+            if (segmentMetadataList.size() == 0) {
+                sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+            }
+
+            priorityQueue.pop();
+            numMessages++;
+
+            DelayedIndex delayedIndex = DelayedIndex.newBuilder()
+                    .setTimestamp(timestamp)
+                    .setLedgerId(ledgerId)
+                    .setEntryId(entryId).build();
+
+            if (entryId <= Integer.MAX_VALUE) {
+                bitMap.compute(ledgerId, (k, v) -> new BitSet()).set((int) entryId);
+            }
+
+            snapshotSegmentBuilder.addIndexes(delayedIndex);
+
+            if (priorityQueue.isEmpty() || priorityQueue.peekN1() > currentTimestampUpperLimit) {
+                segmentMetadataBuilder.setMaxScheduleTimestamp(timestamp);
+                currentTimestampUpperLimit = 0;
+
+                Iterator<Map.Entry<Long, BitSet>> iterator = bitMap.entrySet().iterator();
+                while (iterator.hasNext()) {
+                    Map.Entry<Long, BitSet> entry = iterator.next();
+                    ByteString byteString = ByteString.copyFrom(entry.getValue().toByteArray());
+                    segmentMetadataBuilder.putDelayedIndexBitMap(entry.getKey(), byteString);
+                    iterator.remove();
+                }
+
+                segmentMetadataList.add(segmentMetadataBuilder.build());
+                segmentMetadataBuilder.clear();
+
+                bucketSnapshotSegments.add(snapshotSegmentBuilder.build());
+                snapshotSegmentBuilder.clear();
+            }
+        }
+
+        SnapshotMetadata bucketSnapshotMetadata = SnapshotMetadata.newBuilder()
+                .addAllMetadataList(segmentMetadataList)
+                .build();
+
+        final int lastSegmentEntryId = segmentMetadataList.size();
+
+        Bucket bucket = this.createImmutableBucket(startLedgerId, endLedgerId);
+        bucket.setCurrentSegmentEntryId(1);
+        bucket.setNumberBucketDelayedMessages(numMessages);
+        bucket.setLastSegmentEntryId(lastSegmentEntryId);
+
+        // Add the first snapshot segment last message to snapshotSegmentLastMessageTable
+        checkArgument(!bucketSnapshotSegments.isEmpty());
+        SnapshotSegment snapshotSegment = bucketSnapshotSegments.get(0);
+        DelayedIndex delayedIndex = snapshotSegment.getIndexes(snapshotSegment.getIndexesCount() - 1);
+        snapshotSegmentLastIndexTable.put(delayedIndex.getLedgerId(), delayedIndex.getEntryId(), bucket);
+
+        if (log.isDebugEnabled()) {
+            log.debug("[{}] Create bucket snapshot, bucket: {}", dispatcher.getName(), bucket);
+        }
+
+        String bucketKey = bucket.bucketKey();
+        CompletableFuture<Long> future = asyncSaveBucketSnapshot(bucketKey,
+                bucketSnapshotMetadata, bucketSnapshotSegments);
+        bucket.setSnapshotCreateFuture(future);
+        future.whenComplete((__, ex) -> {
+            if (ex == null) {
+                bucket.setSnapshotCreateFuture(null);
+            } else {
+                //TODO Record create snapshot failed
+                log.error("Failed to create snapshot: ", ex);
+            }
+        });
+
+        return future;
+    }
+
+
+    @SneakyThrows
+    private CompletableFuture<Void> asyncLoadNextBucketSnapshotEntry(Bucket bucket, boolean isRecover) {
+        if (log.isDebugEnabled()) {
+            log.debug("[{}] Load next bucket snapshot data, bucket: {}", dispatcher.getName(), bucket);
+        }
+        if (bucket == null) {
+            return CompletableFuture.completedFuture(null);
+        }
+
+        final CompletableFuture<Long> createFuture = bucket.snapshotCreateFuture;
+        if (createFuture != null) {
+            // Wait bucket snapshot create finish
+            createFuture.get();
+        }
+
+        final String bucketKey = bucket.bucketKey();
+        final Long bucketId = getBucketIdByBucketKey(bucketKey);
+        Objects.requireNonNull(bucketId);
+
+        CompletableFuture<Integer> loadMetaDataFuture = new CompletableFuture<>();
+        if (isRecover) {
+            // TODO Recover bucket snapshot
+        } else {
+            loadMetaDataFuture.complete(bucket.currentSegmentEntryId + 1);
+        }
+
+        CompletableFuture<Void> future = loadMetaDataFuture.thenCompose(nextSegmentEntryId -> {
+            if (nextSegmentEntryId > bucket.lastSegmentEntryId) {
+                // TODO Delete bucket snapshot
+                return CompletableFuture.completedFuture(null);
+            }
+
+            return bucketSnapshotStorage.getBucketSnapshotSegment(bucketId, nextSegmentEntryId, nextSegmentEntryId)
+                    .thenAccept(bucketSnapshotSegments -> {
+                        if (CollectionUtils.isEmpty(bucketSnapshotSegments)) {
+                            return;
+                        }
+
+                        SnapshotSegment snapshotSegment = bucketSnapshotSegments.get(0);
+                        List<DelayedIndex> indexList = snapshotSegment.getIndexesList();
+                        DelayedIndex lastDelayedIndex = indexList.get(indexList.size() - 1);
+
+                        this.snapshotSegmentLastIndexTable.put(lastDelayedIndex.getLedgerId(),
+                                lastDelayedIndex.getEntryId(), bucket);
+
+                        for (DelayedIndex index : indexList) {
+                            sharedBucketPriorityQueue.add(index.getTimestamp(), index.getLedgerId(),
+                                    index.getEntryId());
+                        }
+
+                        bucket.setCurrentSegmentEntryId(nextSegmentEntryId);
+                    });
+        });
+        return future;
+    }
+
+    private void resetLastMutableBucketRange() {
+        lastMutableBucket.setStartLedgerId(-1L);
+        lastMutableBucket.setEndLedgerId(-1L);
+    }
+
+    @Override
+    public synchronized boolean addMessage(long ledgerId, long entryId, long deliverAt) {
+        if (containsMessage(ledgerId, entryId)) {
+            messagesHaveFixedDelay = false;
+            return true;
+        }
+
+        if (deliverAt < 0 || deliverAt <= getCutoffTime()) {
+            messagesHaveFixedDelay = false;
+            return false;
+        }
+
+        boolean existBucket = findBucket(ledgerId).isPresent();
+
+        // Create bucket snapshot
+        if (ledgerId > lastMutableBucket.endLedgerId && !getPriorityQueue().isEmpty()) {
+            if (getPriorityQueue().size() >= minIndexCountPerBucket || existBucket) {
+                if (immutableBuckets.asMapOfRanges().size() >= maxNumBuckets) {
+                    // TODO merge bucket snapshot (synchronize operate)
+                }
+
+                asyncCreateBucketSnapshot();
+                resetLastMutableBucketRange();
+            }
+        }
+
+        if (ledgerId < lastMutableBucket.startLedgerId || existBucket) {
+            // If (ledgerId < startLedgerId || existBucket) means that message index belong to previous bucket range,
+            // enter sharedBucketPriorityQueue directly
+            sharedBucketPriorityQueue.add(deliverAt, ledgerId, entryId);
+        } else {
+            checkArgument(ledgerId >= lastMutableBucket.endLedgerId);
+
+            getPriorityQueue().add(deliverAt, ledgerId, entryId);
+
+            if (lastMutableBucket.startLedgerId == -1L) {
+                lastMutableBucket.setStartLedgerId(ledgerId);
+            }
+            lastMutableBucket.setEndLedgerId(ledgerId);
+        }
+
+        // TODO If the bitSet is sparse, this memory cost very high to deduplication and skip read message
+        lastMutableBucket.putIndexBit(ledgerId, entryId);
+        numberDelayedMessages++;
+
+        if (log.isDebugEnabled()) {
+            log.debug("[{}] Add message {}:{} -- Delivery in {} ms ", dispatcher.getName(), ledgerId, entryId,
+                    deliverAt - clock.millis());
+        }
+
+        updateTimer();
+
+        checkAndUpdateHighest(deliverAt);
+
+        return true;
+    }
+
+    @Override
+    public synchronized boolean hasMessageAvailable() {
+        long cutoffTime = getCutoffTime();
+
+        boolean hasMessageAvailable = !getPriorityQueue().isEmpty() && getPriorityQueue().peekN1() <= cutoffTime;
+
+        hasMessageAvailable = hasMessageAvailable
+                || !sharedBucketPriorityQueue.isEmpty() && sharedBucketPriorityQueue.peekN1() <= cutoffTime;
+        if (!hasMessageAvailable) {
+            updateTimer();
+        }
+        return hasMessageAvailable;
+    }
+
+    @Override
+    protected long nextDeliveryTime() {
+        if (getPriorityQueue().isEmpty() && !sharedBucketPriorityQueue.isEmpty()) {
+            return sharedBucketPriorityQueue.peekN1();
+        } else if (sharedBucketPriorityQueue.isEmpty() && !getPriorityQueue().isEmpty()) {
+            return getPriorityQueue().peekN1();
+        }
+        long timestamp = getPriorityQueue().peekN1();
+        long bucketTimestamp = sharedBucketPriorityQueue.peekN1();
+        return Math.min(timestamp, bucketTimestamp);
+    }
+
+    @Override
+    public synchronized long getNumberOfDelayedMessages() {
+        return numberDelayedMessages;
+    }
+
+    @Override
+    public synchronized long getBufferMemoryUsage() {
+        return getPriorityQueue().bytesCapacity() + sharedBucketPriorityQueue.bytesCapacity();
+    }
+
+    @Override
+    @SneakyThrows
+    public synchronized Set<PositionImpl> getScheduledMessages(int maxMessages) {
+        long cutoffTime = getCutoffTime();
+
+        moveScheduledMessageToSharedQueue(cutoffTime);
+
+        Set<PositionImpl> positions = new TreeSet<>();
+        int n = maxMessages;
+
+        while (n > 0 && !sharedBucketPriorityQueue.isEmpty()) {
+            long timestamp = sharedBucketPriorityQueue.peekN1();
+            if (timestamp > cutoffTime) {
+                break;
+            }
+
+            long ledgerId = sharedBucketPriorityQueue.peekN2();
+            long entryId = sharedBucketPriorityQueue.peekN3();
+            positions.add(new PositionImpl(ledgerId, entryId));
+
+            sharedBucketPriorityQueue.pop();
+            removeIndexBit(ledgerId, entryId);
+
+            Bucket bucket = snapshotSegmentLastIndexTable.remove(ledgerId, entryId);
+            if (bucket != null && bucket.active) {
+                if (log.isDebugEnabled()) {
+                    log.debug("[{}] Load next snapshot segment, bucket: {}", dispatcher.getName(), bucket);
+                }
+                // All message of current snapshot segment are scheduled, load next snapshot segment
+                asyncLoadNextBucketSnapshotEntry(bucket, false).get();

Review Comment:
   It better to make it async



##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/delayed/BucketDelayedDeliveryTracker.java:
##########
@@ -0,0 +1,565 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pulsar.broker.delayed;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static org.apache.bookkeeper.mledger.util.Futures.executeWithRetry;
+import com.google.common.collect.HashBasedTable;
+import com.google.common.collect.Range;
+import com.google.common.collect.RangeMap;
+import com.google.common.collect.Table;
+import com.google.common.collect.TreeRangeMap;
+import com.google.protobuf.ByteString;
+import io.netty.util.Timeout;
+import io.netty.util.Timer;
+import java.time.Clock;
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.concurrent.CompletableFuture;
+import javax.annotation.concurrent.ThreadSafe;
+import lombok.SneakyThrows;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.bookkeeper.mledger.ManagedCursor;
+import org.apache.bookkeeper.mledger.ManagedLedgerException;
+import org.apache.bookkeeper.mledger.impl.PositionImpl;
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.lang.StringUtils;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.DelayedIndex;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotMetadata;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegment;
+import org.apache.pulsar.broker.delayed.proto.DelayedMessageIndexBucketSnapshotFormat.SnapshotSegmentMetadata;
+import org.apache.pulsar.broker.service.persistent.PersistentDispatcherMultipleConsumers;
+import org.apache.pulsar.common.util.collections.TripleLongPriorityQueue;
+
+@Slf4j
+@ThreadSafe
+public class BucketDelayedDeliveryTracker extends InMemoryDelayedDeliveryTracker {
+
+    public static final String DELAYED_BUCKET_KEY_PREFIX = "#pulsar.internal.delayed.bucket";
+
+    public static final String DELIMITER = "_";
+
+    private final long minIndexCountPerBucket;
+
+    private final long timeStepPerBucketSnapshotSegment;
+
+    private final int maxNumBuckets;
+
+    private final ManagedCursor cursor;
+
+    public final BucketSnapshotStorage bucketSnapshotStorage;
+
+    private long numberDelayedMessages;
+
+    private final Bucket lastMutableBucket;
+
+    private final TripleLongPriorityQueue sharedBucketPriorityQueue;
+
+    private final RangeMap<Long, Bucket> immutableBuckets;
+
+    private final Table<Long, Long, Bucket> snapshotSegmentLastIndexTable;
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 long fixedDelayDetectionLookahead,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        this(dispatcher, timer, tickTimeMillis, Clock.systemUTC(), isDelayedDeliveryDeliverAtTimeStrict,
+                fixedDelayDetectionLookahead,
+                bucketSnapshotStorage, minIndexCountPerBucket, timeStepPerBucketSnapshotSegment, maxNumBuckets);
+    }
+
+    BucketDelayedDeliveryTracker(PersistentDispatcherMultipleConsumers dispatcher,
+                                 Timer timer, long tickTimeMillis, Clock clock,
+                                 boolean isDelayedDeliveryDeliverAtTimeStrict,
+                                 long fixedDelayDetectionLookahead,
+                                 BucketSnapshotStorage bucketSnapshotStorage,
+                                 long minIndexCountPerBucket, long timeStepPerBucketSnapshotSegment,
+                                 int maxNumBuckets) {
+        super(dispatcher, timer, tickTimeMillis, clock, isDelayedDeliveryDeliverAtTimeStrict,
+                fixedDelayDetectionLookahead);
+        this.minIndexCountPerBucket = minIndexCountPerBucket;
+        this.timeStepPerBucketSnapshotSegment = timeStepPerBucketSnapshotSegment;
+        this.maxNumBuckets = maxNumBuckets;
+        this.cursor = dispatcher.getCursor();
+        this.sharedBucketPriorityQueue = new TripleLongPriorityQueue();
+        this.immutableBuckets = TreeRangeMap.create();
+        this.snapshotSegmentLastIndexTable = HashBasedTable.create();
+
+        this.bucketSnapshotStorage = bucketSnapshotStorage;
+
+        numberDelayedMessages = 0L;
+
+        this.lastMutableBucket = new Bucket(-1L, -1L, new HashMap<>());
+    }
+
+    private void moveScheduledMessageToSharedQueue(long cutoffTime) {
+        TripleLongPriorityQueue priorityQueue = getPriorityQueue();
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (timestamp > cutoffTime) {
+                break;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+            sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+
+            priorityQueue.pop();
+        }
+    }
+
+    @Override
+    public void run(Timeout timeout) throws Exception {
+        synchronized (this) {
+            moveScheduledMessageToSharedQueue(getCutoffTime());
+        }
+        super.run(timeout);
+    }
+
+    private Optional<Bucket> findBucket(long ledgerId) {
+        if (immutableBuckets.asMapOfRanges().isEmpty()) {
+            return Optional.empty();
+        }
+
+        Range<Long> span = immutableBuckets.span();
+        if (!span.contains(ledgerId)) {
+            return Optional.empty();
+        }
+        return Optional.ofNullable(immutableBuckets.get(ledgerId));
+    }
+
+    private Long getBucketIdByBucketKey(String bucketKey) {
+        String bucketIdStr = cursor.getCursorProperties().get(bucketKey);
+        if (StringUtils.isBlank(bucketIdStr)) {
+            return null;
+        }
+        return Long.valueOf(bucketIdStr);
+    }
+
+    private Bucket createImmutableBucket(long startLedgerId, long endLedgerId) {
+        Bucket newBucket = new Bucket(startLedgerId, endLedgerId, new HashMap<>());
+        immutableBuckets.put(Range.closed(startLedgerId, endLedgerId), newBucket);
+        return newBucket;
+    }
+
+    private CompletableFuture<Long> asyncSaveBucketSnapshot(
+            final String bucketKey, SnapshotMetadata snapshotMetadata,
+            List<SnapshotSegment> bucketSnapshotSegments) {
+        Long bucketId = getBucketIdByBucketKey(bucketKey);
+        checkArgument(bucketId == null);
+
+        return bucketSnapshotStorage.createBucketSnapshot(snapshotMetadata, bucketSnapshotSegments)
+                .thenCompose(newBucketId -> putBucketKeyId(bucketKey, newBucketId));
+    }
+
+    private CompletableFuture<Long> putBucketKeyId(String bucketKey, Long bucketId) {
+        Objects.requireNonNull(bucketId);
+        return executeWithRetry(() -> cursor.putCursorProperty(bucketKey, String.valueOf(bucketId)),
+                ManagedLedgerException.BadVersionException.class).thenApply(__ -> bucketId);
+    }
+
+    private CompletableFuture<Long> asyncCreateBucketSnapshot() {
+        TripleLongPriorityQueue priorityQueue = super.getPriorityQueue();
+        if (priorityQueue.isEmpty()) {
+            return CompletableFuture.completedFuture(null);
+        }
+        long numMessages = 0;
+
+        final long startLedgerId = lastMutableBucket.startLedgerId;
+        final long endLedgerId = lastMutableBucket.endLedgerId;
+
+        List<SnapshotSegment> bucketSnapshotSegments = new ArrayList<>();
+        List<SnapshotSegmentMetadata> segmentMetadataList = new ArrayList<>();
+        Map<Long, BitSet> bitMap = new HashMap<>();
+        SnapshotSegment.Builder snapshotSegmentBuilder = SnapshotSegment.newBuilder();
+        SnapshotSegmentMetadata.Builder segmentMetadataBuilder = SnapshotSegmentMetadata.newBuilder();
+
+        long currentTimestampUpperLimit = 0;
+        while (!priorityQueue.isEmpty()) {
+            long timestamp = priorityQueue.peekN1();
+            if (currentTimestampUpperLimit == 0) {
+                currentTimestampUpperLimit = timestamp + timeStepPerBucketSnapshotSegment - 1;
+            }
+
+            long ledgerId = priorityQueue.peekN2();
+            long entryId = priorityQueue.peekN3();
+
+            checkArgument(ledgerId >= startLedgerId && ledgerId <= endLedgerId);
+
+            // Move first segment of bucket snapshot to sharedBucketPriorityQueue
+            if (segmentMetadataList.size() == 0) {
+                sharedBucketPriorityQueue.add(timestamp, ledgerId, entryId);
+            }
+
+            priorityQueue.pop();
+            numMessages++;
+
+            DelayedIndex delayedIndex = DelayedIndex.newBuilder()
+                    .setTimestamp(timestamp)
+                    .setLedgerId(ledgerId)
+                    .setEntryId(entryId).build();
+
+            if (entryId <= Integer.MAX_VALUE) {
+                bitMap.compute(ledgerId, (k, v) -> new BitSet()).set((int) entryId);
+            }
+
+            snapshotSegmentBuilder.addIndexes(delayedIndex);
+
+            if (priorityQueue.isEmpty() || priorityQueue.peekN1() > currentTimestampUpperLimit) {
+                segmentMetadataBuilder.setMaxScheduleTimestamp(timestamp);
+                currentTimestampUpperLimit = 0;
+
+                Iterator<Map.Entry<Long, BitSet>> iterator = bitMap.entrySet().iterator();
+                while (iterator.hasNext()) {
+                    Map.Entry<Long, BitSet> entry = iterator.next();
+                    ByteString byteString = ByteString.copyFrom(entry.getValue().toByteArray());
+                    segmentMetadataBuilder.putDelayedIndexBitMap(entry.getKey(), byteString);
+                    iterator.remove();
+                }
+
+                segmentMetadataList.add(segmentMetadataBuilder.build());
+                segmentMetadataBuilder.clear();
+
+                bucketSnapshotSegments.add(snapshotSegmentBuilder.build());
+                snapshotSegmentBuilder.clear();
+            }
+        }
+
+        SnapshotMetadata bucketSnapshotMetadata = SnapshotMetadata.newBuilder()
+                .addAllMetadataList(segmentMetadataList)
+                .build();
+
+        final int lastSegmentEntryId = segmentMetadataList.size();
+
+        Bucket bucket = this.createImmutableBucket(startLedgerId, endLedgerId);
+        bucket.setCurrentSegmentEntryId(1);
+        bucket.setNumberBucketDelayedMessages(numMessages);
+        bucket.setLastSegmentEntryId(lastSegmentEntryId);
+
+        // Add the first snapshot segment last message to snapshotSegmentLastMessageTable
+        checkArgument(!bucketSnapshotSegments.isEmpty());
+        SnapshotSegment snapshotSegment = bucketSnapshotSegments.get(0);
+        DelayedIndex delayedIndex = snapshotSegment.getIndexes(snapshotSegment.getIndexesCount() - 1);
+        snapshotSegmentLastIndexTable.put(delayedIndex.getLedgerId(), delayedIndex.getEntryId(), bucket);
+
+        if (log.isDebugEnabled()) {
+            log.debug("[{}] Create bucket snapshot, bucket: {}", dispatcher.getName(), bucket);
+        }
+
+        String bucketKey = bucket.bucketKey();
+        CompletableFuture<Long> future = asyncSaveBucketSnapshot(bucketKey,
+                bucketSnapshotMetadata, bucketSnapshotSegments);
+        bucket.setSnapshotCreateFuture(future);
+        future.whenComplete((__, ex) -> {
+            if (ex == null) {
+                bucket.setSnapshotCreateFuture(null);
+            } else {
+                //TODO Record create snapshot failed
+                log.error("Failed to create snapshot: ", ex);
+            }
+        });
+
+        return future;
+    }
+
+
+    @SneakyThrows
+    private CompletableFuture<Void> asyncLoadNextBucketSnapshotEntry(Bucket bucket, boolean isRecover) {
+        if (log.isDebugEnabled()) {
+            log.debug("[{}] Load next bucket snapshot data, bucket: {}", dispatcher.getName(), bucket);
+        }
+        if (bucket == null) {
+            return CompletableFuture.completedFuture(null);
+        }
+
+        final CompletableFuture<Long> createFuture = bucket.snapshotCreateFuture;
+        if (createFuture != null) {
+            // Wait bucket snapshot create finish
+            createFuture.get();
+        }
+
+        final String bucketKey = bucket.bucketKey();
+        final Long bucketId = getBucketIdByBucketKey(bucketKey);
+        Objects.requireNonNull(bucketId);
+
+        CompletableFuture<Integer> loadMetaDataFuture = new CompletableFuture<>();
+        if (isRecover) {
+            // TODO Recover bucket snapshot
+        } else {
+            loadMetaDataFuture.complete(bucket.currentSegmentEntryId + 1);
+        }
+
+        CompletableFuture<Void> future = loadMetaDataFuture.thenCompose(nextSegmentEntryId -> {

Review Comment:
   we can return directly.



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