[GitHub] [kafka] vcrfxia commented on a diff in pull request #13756: KAFKA-14936: Add On Disk Time Ordered Buffer (1/N)

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

vcrfxia commented on code in PR #13756:
URL: https://github.com/apache/kafka/pull/13756#discussion_r1212267772


##########
streams/src/main/java/org/apache/kafka/streams/state/internals/RocksDBTimeOrderedKeyValueBuffer.java:
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@@ -0,0 +1,188 @@
+/*
+ * 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.kafka.streams.state.internals;
+
+import org.apache.kafka.common.serialization.Serde;
+import org.apache.kafka.common.utils.Bytes;
+import org.apache.kafka.streams.KeyValue;
+import org.apache.kafka.streams.kstream.internals.Change;
+import org.apache.kafka.streams.kstream.internals.FullChangeSerde;
+import org.apache.kafka.streams.processor.ProcessorContext;
+import org.apache.kafka.streams.processor.StateStore;
+import org.apache.kafka.streams.processor.StateStoreContext;
+import org.apache.kafka.streams.processor.api.Record;
+import org.apache.kafka.streams.processor.internals.ProcessorRecordContext;
+import org.apache.kafka.streams.processor.internals.SerdeGetter;
+import org.apache.kafka.streams.state.KeyValueIterator;
+import org.apache.kafka.streams.state.ValueAndTimestamp;
+
+import java.nio.ByteBuffer;
+import java.time.Duration;
+import java.util.function.Consumer;
+import java.util.function.Supplier;
+
+import static java.util.Objects.requireNonNull;
+
+public class RocksDBTimeOrderedKeyValueBuffer<K, V> extends WrappedStateStore<RocksDBTimeOrderedKeyValueSegmentedBytesStore, Object, Object> implements TimeOrderedKeyValueBuffer<K, V> {
+
+    private final Duration gracePeriod;
+    private long bufferSize;
+    private long minTimestamp;
+    private int numRec;
+    private Serde<K> keySerde;
+    private FullChangeSerde<V> valueSerde;

Review Comment:
   Hmm, interesting that the serde type here is for `Change<V>` instead of plain `V`. Looks like the reason that's the case is because `TimeOrderedKeyValueBuffer` stores `Change<V>`. What do you think about updating `TimeOrderedKeyValueBuffer` to take a third generic type to represent the type stored in the actual buffer itself, in order to allow this new buffer implementation to simply store `V` instead? (The buffer type would be `Change<V>` for the existing implementations, and just `V` for this new implementation.)
   
   That would simplify a lot of code in this class which doesn't have use cases for old values anyway (also evidenced by the fact that `priorValueForBuffered()` always returns null), and callers of this class won't need to pass in `null` for the old value in `Change` either. It'll also make the serialized value smaller, since we won't have to serialize in nulls for `oldValue` and `priorValue` anymore.



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