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https://issues.apache.org/jira/browse/SOLR-11216?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16507649#comment-16507649
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Cao Manh Dat commented on SOLR-11216:
-------------------------------------
The problem here relates to "on-wire" updates which get returned in
"getVersions" request but do not present in replica's buffering tlog. Here are
couples of solution
* Solution 1: After submitting "getVersions" request, the replica will wait for
some time. Therefore "on-wire" updates will land on buffering tlog. This is the
simplest solution but less robust than solution 2.
* Solution 2: On finding missed updates, the replica will consider buffered
updates as missed one. Hence will request these updates from the leader and
apply them to its local index -> It will make the fingerprint comparison
success.
* Solution 3: On finding missed updates, the replica will consider any updates
with version larger than minVersion(buffered updates) are non-missed updates
(the "on-wire" updates will be filled on applyBufferedUpdates() call). We only
do fingerprint comparison up-to minVersion(buffered updates).
[~praste] Yeah, that case will be very tricky to solve, but at least we should
solve some common cases.
> 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
> Priority: Major
>
> 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,
> ## in the same time leader receive update 9, so it will return updates from 1
> to 9 (for request versions) when replica get recent versions ( so it will be
> 1,2,3,4,5,6,7,8,9 )
> ## 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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