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Posted to dev@lucene.apache.org by "Mark Miller (JIRA)" <ji...@apache.org> on 2017/09/29 00:20:00 UTC
[jira] [Commented] (SOLR-11417) Crashed leader's hanging emphemral
will make restarting followers stuck in recovering
[ https://issues.apache.org/jira/browse/SOLR-11417?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16185154#comment-16185154 ]
Mark Miller commented on SOLR-11417:
------------------------------------
I'd have to look closer, but my first thought would be, we should make sure that if a replica comes up and attempts to be leader but fails due to a connection issue, it should make sure it can still successfully be a leader in a later attempt.
bq. will read stale data from ZK about current leader
We can always read stale data, so we have to make sure still operate correctly in the face of that.
bq. will fail recovery and stuck in recovering state
I guess the key question is, why are we stuck in recovering? What happens so that we cannot be leader when the ephemeral goes away? Do we overwrite the last active stat as not ACTIVE? In that case, it seems we should try and prevent that when a replica simply has connection problems with the leader vs failing a sync or something.
> Crashed leader's hanging emphemral will make restarting followers stuck in recovering
> -------------------------------------------------------------------------------------
>
> Key: SOLR-11417
> URL: https://issues.apache.org/jira/browse/SOLR-11417
> Project: Solr
> Issue Type: Bug
> Security Level: Public(Default Security Level. Issues are Public)
> Affects Versions: 6.3
> Reporter: Mano Kovacs
> Attachments: SOLR-11417.png
>
>
> If replicas are starting up after leader crash and within the ZK session timeout, replicas
> * will lose leader election due to hanging ephemerals
> * will read stale data from ZK about current leader
> * will fail recovery and stuck in recovering state
> If leader is down permanently (eg. hardware failure) and all replicas are affected, shard will not come up (see also SOLR-7065).
> Tested on 6.3. See attached image for details.
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