[GitHub] [kafka] jsancio commented on a change in pull request #10899: KAFKA-12952 Adding Delimeters to Metadata Snapshot File

[GitBox]

jsancio commented on a change in pull request #10899:
URL: https://github.com/apache/kafka/pull/10899#discussion_r655542285



##########
File path: 
raft/src/main/java/org/apache/kafka/raft/internals/BatchAccumulator.java
##########
@@ -233,6 +235,68 @@ public void appendLeaderChangeMessage(LeaderChangeMessage 
leaderChangeMessage, l
         }
     }
 
+
+    public void appendSnapshotHeaderMessage(MetadataSnapshotHeaderRecord 
snapshotHeaderRecord) {
+        appendLock.lock();
+        try {
+            // Ideally there should be nothing in the batch here.
+            // TODO verify this

Review comment:
       It is a valid/correct check but it doesn't cover all of the cases. For 
example, in theory `SnapshotWriter` could do the following:
   ```
   accumulator.appendSnapshotHeaderMessage(...);
   snapshot.appendBatches(accumulator.drain());
   accumulator.appendSnapshotHeaderMessage(...);
   ```
   
   This is okay from the `BatchAccumulator`'s point of view because the 
accumulator doesn't have enough information. I am also not sure if we want to 
encode the invariant of `SnapshotHeaderMessage` and `SnaspshotFooterMessage` 
into the `BatchAccumulator`.
   
   I think only the `SnapshotWriter` has enough information to make these 
invariant checks. What do you think?
   




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