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https://issues.apache.org/jira/browse/RATIS-748?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16969946#comment-16969946
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Lokesh Jain edited comment on RATIS-748 at 11/8/19 9:15 AM:
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This issue was found while debugging RATIS-727. One of the followers has the
following metadata -
flushIndex - 1371
commitIndex - 269
leaderCommitIndex - 1618
endIndex(open segment) - 1371
The follower flushIndex has reached 1370 but its commitIndex is still not
updated. Entry corresponding to 1618 index will not be found in the raft log as
endIndex for the open segment is at 1371.
was (Author: ljain):
This issue was found while debugging RATIS-727. One of the followers has the
following metadata -
flushIndex - 1371
commitIndex - 269
leaderCommitIndex - 1618
The follower flushIndex has reached 1370 but its commitIndex is still not
updated.
> Follower might not update its commit index
> ------------------------------------------
>
> Key: RATIS-748
> URL: https://issues.apache.org/jira/browse/RATIS-748
> Project: Ratis
> Issue Type: Bug
> Reporter: Lokesh Jain
> Priority: Critical
> Attachments: RATIS-748.001.patch
>
>
> While updating the commit index, the follower checks whether majority index
> is present in the raft log. There can be cases where leader is ahead of the
> follower and follower does not have the entry corresponding to the
> majorityIndex. In such cases the follower commit index is not updated. Below
> is the corresponding code snippet.
> {code:java}
> public boolean updateLastCommitted(long majorityIndex, long currentTerm) {
> try(AutoCloseableLock writeLock = writeLock()) {
> final long oldCommittedIndex = getLastCommittedIndex();
> if (oldCommittedIndex < majorityIndex) {
> // Only update last committed index for current term. See §5.4.2 in
> // paper for details.
> final TermIndex entry = getTermIndex(majorityIndex);
> if (entry != null && entry.getTerm() == currentTerm) {
> final long newCommitIndex = Math.min(majorityIndex, getFlushIndex());
> if (newCommitIndex > oldCommittedIndex) {
> commitIndex.updateIncreasingly(newCommitIndex, traceIndexChange);
> }
> return true;
> }
> }
> }
> return false;
> }{code}
> This function RaftLog#updateLastCommitted is also used by follower to update
> its commit index. The follower does not require the check of entry.getTerm()
> == currentTerm and its commitIndex can be updated to min(majorityIndex,
> getFlushIndex()). It has already verified the entries in the
> appendEntriesAsync call.
> This can lead to the follower commit being updated in bursts and can lead to
> failure of watch requests.
> cc [~shashikant] [~szetszwo]
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