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https://issues.apache.org/jira/browse/SOLR-3721?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13440531#comment-13440531
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Mark Miller commented on SOLR-3721:
-----------------------------------
I've been reviewing this code, and so far there is only way I can see that
would seem to allow multiple recoveries at once - if there is an interrupt when
cancelRecovery is doing a join, it seems another recovery could be started and
briefly overlap. Since we already call close on the recovery thread, the
overlap would be brief at best. An interrupt like this should be somewhat rare
- but interrupts do happen on jetty shutdown. I'm going to guess this is not
what you were seeing, but I'll plug it.
> Multiple concurrent recoveries of same shard?
> ---------------------------------------------
>
> Key: SOLR-3721
> URL: https://issues.apache.org/jira/browse/SOLR-3721
> Project: Solr
> Issue Type: Bug
> Components: multicore, SolrCloud
> Affects Versions: 4.0
> Environment: Using our own Solr release based on Apache revision
> 1355667 from 4.x branch. Our changes to the Solr version is our solutions to
> TLT-3178 etc., and should have no effect on this issue.
> Reporter: Per Steffensen
> Labels: concurrency, multicore, recovery, solrcloud
> Fix For: 4.0
>
> Attachments: recovery_in_progress.png, recovery_start_finish.log
>
>
> We run a performance/endurance test on a 7 Solr instance SolrCloud setup and
> eventually Solrs lose ZK connections and go into recovery. BTW the recovery
> often does not ever succeed, but we are looking into that. While doing that I
> noticed that, according to logs, multiple recoveries are in progress at the
> same time for the same shard. That cannot be intended and I can certainly
> imagine that it will cause some problems.
> It is just the logs that are wrong, did I make some mistake, or is this a
> real bug?
> See attached grep from log, grepping only on "Finished recovery" and
> "Starting recovery" logs.
> {code}
> grep -B 1 "Finished recovery\|Starting recovery" solr9.log solr8.log
> solr7.log solr6.log solr5.log solr4.log solr3.log solr2.log solr1.log
> solr0.log > recovery_start_finish.log
> {code}
> It can be hard to get an overview of the log, but I have generated a graph
> showing (based alone on "Started recovery" and "Finished recovery" logs) how
> many recoveries are in progress at any time for the different shards. See
> attached recovery_in_progress.png. The graph is also a little hard to get an
> overview of (due to the many shards) but it is clear that for several shards
> there are multiple recoveries going on at the same time, and that several
> recoveries never succeed.
> Regards, Per Steffensen
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