[GitHub] [incubator-paimon] liming30 commented on a diff in pull request #1450: [flink] supports alignment with flink checkpoint when consuming paimon snapshots.

["liming30 (via GitHub)" <gi...@apache.org>]

liming30 commented on code in PR #1450:
URL: https://github.com/apache/incubator-paimon/pull/1450#discussion_r1258099141


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paimon-flink/paimon-flink-common/src/main/java/org/apache/paimon/flink/source/align/AlignedSourceReader.java:
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@@ -0,0 +1,298 @@
+/*
+ * 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.paimon.flink.source.align;
+
+import org.apache.paimon.table.source.EndOfScanException;
+import org.apache.paimon.table.source.ReadBuilder;
+import org.apache.paimon.table.source.SnapshotNotExistPlan;
+import org.apache.paimon.table.source.Split;
+import org.apache.paimon.table.source.StreamTableScan;
+import org.apache.paimon.table.source.TableScan;
+
+import org.apache.flink.api.common.eventtime.Watermark;
+import org.apache.flink.api.connector.source.ExternallyInducedSourceReader;
+import org.apache.flink.api.connector.source.ReaderOutput;
+import org.apache.flink.api.connector.source.SourceEvent;
+import org.apache.flink.core.io.InputStatus;
+import org.apache.flink.runtime.io.AvailabilityProvider;
+import org.apache.flink.util.Preconditions;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.Optional;
+import java.util.TreeMap;
+import java.util.TreeSet;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.TimeUnit;
+
+import static org.apache.flink.runtime.io.AvailabilityProvider.AVAILABLE;
+import static org.apache.paimon.flink.FlinkConnectorOptions.CheckpointAlignMode;
+
+/**
+ * A non-parallel {@link org.apache.flink.api.connector.source.SourceReader} that uses Flip-27 to
+ * achieve the same function as {@link org.apache.paimon.flink.source.operator.MonitorFunction}.
+ *
+ * <p>Send {@link Split} to the downstream task at paimon snapshot granularity, and provide two
+ * alignment modes: {@link CheckpointAlignMode#STRICTLY} and {@link CheckpointAlignMode#LOOSELY}.
+ *
+ * <ol>
+ *   <li>STRICTLY: only one paimon snapshot is processed within a checkpoint interval.
+ *   <li>LOOSELY: several paimon snapshots are processed within a checkpoint interval.
+ * </ol>
+ */
+@SuppressWarnings("unchecked")
+public abstract class AlignedSourceReader
+        implements ExternallyInducedSourceReader<Split, AlignedSourceSplit> {
+
+    private static final Logger LOG = LoggerFactory.getLogger(AlignedSourceReader.class);
+    private static final int MAX_PENDING_PLANS = 10;
+
+    private final ReadBuilder readBuilder;
+
+    private final FutureCompletingBlockingDeque<AlignedSourceSplit> pendingSplits;
+
+    private final TreeSet<Long> pendingCheckpoints;
+
+    private final TreeMap<Long, Long> nextSnapshotPerCheckpoint;
+
+    private final long scanInterval;
+
+    private final boolean emitSnapshotWatermark;
+
+    private final ScheduledExecutorService executors;
+
+    private Long snapshotIdByNextCheckpoint;
+
+    private boolean blocking;
+
+    private boolean endOfScan;
+
+    private CompletableFuture<Void> availabilityFuture;
+
+    private transient StreamTableScan scan;
+
+    public AlignedSourceReader(
+            ReadBuilder readBuilder,
+            long scanInterval,
+            boolean emitSnapshotWatermark,
+            ScheduledExecutorService executors) {
+        this.readBuilder = readBuilder;
+        this.pendingSplits = new FutureCompletingBlockingDeque<>();
+        this.pendingCheckpoints = new TreeSet<>();
+        this.availabilityFuture = (CompletableFuture<Void>) AVAILABLE;
+        this.nextSnapshotPerCheckpoint = new TreeMap<>();
+        this.scanInterval = scanInterval;
+        this.emitSnapshotWatermark = emitSnapshotWatermark;
+        this.executors = executors;
+        this.snapshotIdByNextCheckpoint = null;
+        this.blocking = false;
+        this.endOfScan = false;
+    }
+
+    @Override
+    public void start() {
+        this.scan = readBuilder.newStreamScan();

Review Comment:
   If the splits are still scanned and assigned by the `Enumerator`, there is a problem: in the `strictly-align` mode, if the source table has not produced the corresponding snapshot at the time of the checkpoint, then the checkpoint will wait until the timeout.



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