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https://issues.apache.org/jira/browse/SOLR-11216?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16260117#comment-16260117
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Pushkar Raste commented on SOLR-11216:
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[~caomanhdat]
Can this fail if the leader processes updates out of order e.g. what if leader
processed updates in the order 6 and has yet to process 5. Now the replica
requests update 6. However, leader has just finished processing 5 (including a
soft/hard commit) and when leader calculates index fingerprint up to 6, the
leader's fingerprint will include version 5 as well.
Considering all the race conditions, I think making fingerprint robust is
tricky.
> Make PeerSync more robust
> -------------------------
>
> Key: SOLR-11216
> URL: https://issues.apache.org/jira/browse/SOLR-11216
> Project: Solr
> Issue Type: Improvement
> Security Level: Public(Default Security Level. Issues are Public)
> Reporter: Cao Manh Dat
>
> First of all, I will change the issue's title with a better name when I have.
> When digging into SOLR-10126. I found a case that can make peerSync fail.
> * leader and replica receive update from 1 to 4
> * replica stop
> * replica miss updates 5, 6
> * replica start recovery
> ## replica buffer updates 7, 8
> ## replica request versions from leader,
> ## replica get recent versions which is 1,2,3,4,7,8
> ## in the same time leader receive update 9, so it will return updates from 1
> to 9 (for request versions)
> ## replica do peersync and request updates 5, 6, 9 from leader
> ## replica apply updates 5, 6, 9. Its index does not have update 7, 8 and
> maxVersionSpecified for fingerprint is 9, therefore compare fingerprint will
> fail
> My idea here is why replica request update 9 (step 6) while it knows that
> updates with lower version ( update 7, 8 ) are on its buffering tlog. Should
> we request only updates that lower than the lowest update in its buffering
> tlog ( < 7 )?
> Someone my ask that what if replica won't receive update 9. In that case,
> leader will put the replica into LIR state, so replica will run recovery
> process again.
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