[jira] [Commented] (SOLR-12729) SplitShardCmd should lock the parent shard to prevent parallel splitting requests

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[jira] [Commented] (SOLR-12729) SplitShardCmd should lock the parent shard to prevent parallel splitting requests

Sebastian Nagel (Jira)

    [ https://issues.apache.org/jira/browse/SOLR-12729?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16658773#comment-16658773 ]

ASF subversion and git services commented on SOLR-12729:
--------------------------------------------------------

Commit 8c70811f3a2a4deab8186b187909ac5c3615e6fb in lucene-solr's branch refs/heads/master from Andrzej Bialecki
[ https://git-wip-us.apache.org/repos/asf?p=lucene-solr.git;h=8c70811 ]

SOLR-12729: Unlock the shard on error.


> SplitShardCmd should lock the parent shard to prevent parallel splitting requests
> ---------------------------------------------------------------------------------
>
>                 Key: SOLR-12729
>                 URL: https://issues.apache.org/jira/browse/SOLR-12729
>             Project: Solr
>          Issue Type: Bug
>      Security Level: Public(Default Security Level. Issues are Public)
>          Components: AutoScaling
>            Reporter: Andrzej Bialecki
>            Assignee: Andrzej Bialecki
>            Priority: Major
>             Fix For: 7.6, master (8.0)
>
>
> This scenario was discovered by the simulation framework, but it exists also in the non-simulated code.
> When {{IndexSizeTrigger}} requests SPLITSHARD, which is then successfully started and “completed” from the point of view of {{ExecutePlanAction}}, the reality is that it still can take significant amount of time until the moment when the new replicas fully recover and cause the switch of shard states (parent to INACTIVE, child from RECOVERY to ACTIVE).
> If this time is longer than the trigger's {{waitFor}} the trigger will issue the same SPLITSHARD request again. {{SplitShardCmd}} doesn't prevent this new request from being processed because the parent shard is still ACTIVE. However, a section of the code in {{SplitShardCmd}} will realize that sub-slices with the target names already exist and they are not active, at which point it will delete the new sub-slices ({{SplitShardCmd:182}}).
> The end result is an infinite loop, where {{IndexSizeTrigger}} will keep generating SPLITSHARD, and {{SplitShardCmd}} will keep deleting the recovering sub-slices created by the previous command.
> A simple solution is for the parent shard to be marked to indicate that it’s in a process of splitting, so that no other split is attempted on the same shard. Furthermore, {{IndexSizeTrigger}} could temporarily exclude such shards from monitoring.



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