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https://issues.apache.org/jira/browse/SOLR-12969?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16683475#comment-16683475
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Cao Manh Dat commented on SOLR-12969:
-------------------------------------
Actually, I have another idea for not relying on tlog for PeerSync. This idea
requires 2 changes
* Versions should be monotonic increased (instead of relying on clock time).
* Each commit point will contains the compressed format of all the updates
versions had been applied. I.E: 1..100,103..1000.
* Therefore based on above changes, we can quickly compare version that we
missed without caring about compute fingerprint or relying on tlog.
* We still need to think about cases with FORCELEADER or similar cases, i.e:
different updates have same update version.
But this approach requires a lot of changes and I'm not sure it is worth or
not. What we gain here by going with above approach is
* Faster and more reliable PeerSync process.
* We don't have to compute fingerprint any more.
May be one or two more cases will convince me on switching to above approach.
Any thoughts? [~shalinmangar] [[email protected]] [[email protected]]
> Solr replication failure
> ------------------------
>
> Key: SOLR-12969
> URL: https://issues.apache.org/jira/browse/SOLR-12969
> Project: Solr
> Issue Type: Bug
> Security Level: Public(Default Security Level. Issues are Public)
> Components: replication (java)
> Reporter: Jeremy Smith
> Assignee: Cao Manh Dat
> Priority: Major
> Attachments: SOLR-12969.patch, SOLR-12969.patch, SOLR-12969.patch
>
>
> Under certain circumstances, replication fails between a leader and follower.
> The follower will not receive updates from the leader, even though the
> leader has a newer version. If the leader is restarted, it will get the
> older version from the follower.
>
> This was discussed on the [mailing
> list|https://mail-archives.apache.org/mod_mbox/lucene-solr-user/201810.mbox/%3CBYAPR04MB4406710795EA07E93BF80913ADCD0%40BYAPR04MB4406.namprd04.prod.outlook.com%3E]
> and [~risdenk] [wrote a
> script|https://github.com/risdenk/test-solr-start-stop-replica-consistency]
> that demonstrates this error. He also verified that the error occurs when
> the script is run outside of docker.
>
> Here is the scenario of the failure:
> * A collection with 1 shards and 2 replicas
> * Stop non-leader replica (B)
> * Index more than 100 documents to the collection
> * Start replica B, it failed to do PeerSync and starts segments replication
> * Index document 101th to the collection
> ** Leader's tlog: [1, 2, 3, ..., 100, 101]
> ** Replica's tlog: [101]
> * Stop replica B
> * Index document 102th to the collection
> * Start replica B, on doing PeerSync
> ** Leader's tlog: [1, 2, 3, ..., 100, 101, 102]
> ** Replica's tlog: [101]
> ** Leader's high (80th): 80
> ** Replica's low: 101
> ** By comparison: replica's low > leader's high => ALREADY_IN_SYNC
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