divijvaidya commented on code in PR #13456:
URL: https://github.com/apache/kafka/pull/13456#discussion_r1151705356
##########
storage/src/main/java/org/apache/kafka/storage/internals/epoch/LeaderEpochFileCache.java:
##########
@@ -383,11 +396,11 @@ public void clear() {
// Visible for testing
public List<EpochEntry> epochEntries() {
- lock.writeLock().lock();
+ lock.readLock().lock();
Review Comment:
Nice!
Could we move this to a separate PR please since I think this is an obvious
change that can be shipped earlier than this PR.
##########
storage/src/main/java/org/apache/kafka/storage/internals/epoch/LeaderEpochFileCache.java:
##########
@@ -148,6 +151,16 @@ private List<EpochEntry>
removeWhileMatching(Iterator<Map.Entry<Integer, EpochEn
return removedEpochs;
}
+ public LeaderEpochFileCache writeTo(LeaderEpochCheckpoint
leaderEpochCheckpoint) {
+ lock.writeLock().lock();
Review Comment:
You don't need write locks here since you are flushing to an entirely new
checkpoint. You need read lock on existing cache. (similar to flush() method)
##########
storage/src/main/java/org/apache/kafka/storage/internals/epoch/LeaderEpochFileCache.java:
##########
@@ -148,6 +151,16 @@ private List<EpochEntry>
removeWhileMatching(Iterator<Map.Entry<Integer, EpochEn
return removedEpochs;
}
+ public LeaderEpochFileCache writeTo(LeaderEpochCheckpoint
leaderEpochCheckpoint) {
+ lock.writeLock().lock();
+ try {
+ leaderEpochCheckpoint.write(epochEntries());
Review Comment:
It seems like we are doing the following:
1. Flush the cache values to the checkpoint.
2. Create a new file cache which would read from the checkpoint created in
step 1
which means, we are probably trying to have a copy of this cache backed by
this new checkpoint here.
Alternatively, may I suggest the following:
```
public LeaderEpochFileCache
cloneWithLeaderEpochCheckpoint(LeaderEpochCheckpoint leaderEpochCheckpoint) {
this.flushToCheckpoint(leaderEpochCheckpoint);
return new LeaderEpochFileCache(this.topicPartition,
leaderEpochCheckpoint);
}
```
`flushToCheckpoint()` is similar to existing flush() method.
##########
storage/src/main/java/org/apache/kafka/storage/internals/checkpoint/InMemoryLeaderEpochCheckpoint.java:
##########
@@ -0,0 +1,58 @@
+/*
+ * 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.storage.internals.checkpoint;
+
+import org.apache.kafka.server.common.CheckpointFile;
+import org.apache.kafka.storage.internals.log.EpochEntry;
+
+import java.io.BufferedWriter;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.OutputStreamWriter;
+import java.nio.ByteBuffer;
+import java.nio.charset.StandardCharsets;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
+
+/**
+ * This class stores a list of EpochEntry(LeaderEpoch + Offsets) to memory
+ */
+public class InMemoryLeaderEpochCheckpoint implements LeaderEpochCheckpoint {
Review Comment:
Please help me clarify my understanding here. I don't understand the
motivation here.
File based checkpoints are used for faster recovery so that when a restart
occurs, we are don't lose the in-memory state and can recover from a
checkpoint. The concept of in-memory checkpoint contradicts the entire purpose
of having a checkpoint logic! If we are keeping this in-memory, then why even
bother checkpointing at all?
##########
core/src/main/scala/kafka/log/remote/RemoteLogManager.scala:
##########
@@ -219,6 +221,29 @@ class RemoteLogManager(rlmConfig: RemoteLogManagerConfig,
}
}
+ /**
+ * Returns the in memory leader epoch checkpoint by truncating with the
given start[exclusive] and end[inclusive] offset
+ *
+ * @param log The actual log from where to take the leader-epoch
checkpoint
+ * @param startOffset The start offset of the checkpoint file (exclusive in
the truncation).
+ * If start offset is 6, then it will retain an entry at
offset 6.
+ * @param endOffset The end offset of the checkpoint file (inclusive in
the truncation)
+ * If end offset is 100, then it will remove the entries
greater than or equal to 100.
+ * @return the truncated leader epoch checkpoint
+ */
+ private[remote] def getLeaderEpochCheckpoint(log: UnifiedLog, startOffset:
Long, endOffset: Long): InMemoryLeaderEpochCheckpoint = {
Review Comment:
where we going to use this? The motivation for this PR is unclear to me.
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