chungen0126 commented on code in PR #1130:
URL: https://github.com/apache/ratis/pull/1130#discussion_r1704855115
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ratis-server/src/main/java/org/apache/ratis/server/raftlog/RaftLogBase.java:
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@@ -230,6 +230,9 @@ private long appendMetadataImpl(long term, long
newCommitIndex) {
final long nextIndex;
try(AutoCloseableLock writeLock = writeLock()) {
nextIndex = getNextIndex();
+ if (nextIndex - 1 != newCommitIndex) {
+ return INVALID_LOG_INDEX;
+ }
Review Comment:
> Let's add more information to your example. Suppose`entriesToCommit` are
>
> * STATEMACHINELOGENTRY(1, 1)
> * STATEMACHINELOGENTRY(1, 2)
> * METADATAENTRY(term: 1, index: 3, commitIndex: 1)
>
> and
>
> * `nextIndex` is 4.
In your case, `entriesToCommit` will become:
- STATEMACHINELOGENTRY(1, 1)
- STATEMACHINELOGENTRY(1, 2)
- METADATAENTRY(term: 1, index: 3, commitIndex: 2)
> Then, `newCommitIndex` is 2 and `nextIndex - 1 != newCommitIndex` is
false. It won't append the metadata entry in this case. Why checking the
if-condition here?
The metadata entry (term: 1, index: 3, commitIndex: 1) will not be appended
because the condition `nextIndex - 1 != newCommitIndex` is false. Specifically,
nextIndex - 1 (2) is not equal to newCommitIndex (1).
Ideally, when there are consecutive commits, it will only log one metadata
with last commit index. However, if the `commitIndex` was always slower than
the nextIndex, it won't append the metadata entry until `commitIndex` catches
up.
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