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From Jan Høydahl (JIRA) <j...@apache.org>
Subject [jira] [Commented] (SOLR-3721) Multiple concurrent recoveries of same shard?
Date Thu, 16 Aug 2012 22:44:38 GMT

    [ https://issues.apache.org/jira/browse/SOLR-3721?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13436383#comment-13436383
] 

Jan Høydahl commented on SOLR-3721:
-----------------------------------

ElasticSearch has some settings to control when recovery starts after cluster restart, see
[Guide|http://www.elasticsearch.org/guide/reference/modules/gateway/]. This approach looks
reasonable. If we know that we expect N nodes in our cluster we can start recovery when we
see N nodes up. If fewer than N nodes up, we wait for X time (running on local data, not accepting
new updates) before recovery and leader election starts.
                
> 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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