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https://issues.apache.org/jira/browse/PHOENIX-4537?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16331400#comment-16331400
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James Taylor commented on PHOENIX-4537:
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[~karanmehta93], [~tdsilva]
> RegionServer initiating compaction can trigger schema migration and deadlock
> the system
> ---------------------------------------------------------------------------------------
>
> Key: PHOENIX-4537
> URL: https://issues.apache.org/jira/browse/PHOENIX-4537
> Project: Phoenix
> Issue Type: Bug
> Reporter: Romil Choksi
> Priority: Critical
> Fix For: 5.0.0, 4.14.0
>
>
> [~sergey.soldatov] has been doing some great digging around a test failure
> we've been seeing at $dayjob. The situation goes like this.
> 0. Run some arbitrary load
> 1. Stop HBase
> 2. Enable schema mapping ({{phoenix.schema.isNamespaceMappingEnabled=true}}
> and {{phoenix.schema.mapSystemTablesToNamespace=true}} in hbase-site.xml)
> 3. Start HBase
> 4. Circumstantially, have the SYSTEM.CATALOG table need a compaction to run
> before a client first connects
> When the RegionServer initiates the compaction, it will end up running
> {{UngroupedAggregateRegionObserver.clearTsOnDisabledIndexes}} which opens a
> Phoenix connection. While the RegionServer won't upgrade system tables, it
> *will* try to migrate them into the schema mapped variants (e.g.
> SYSTEM.CATALOG to SYSTEM:CATALOG).
> However, one of the first steps in the schema migration is to disable the
> SYSTEM.CATALOG table. However, the SYSTEM.CATALOG table can't be disabled
> until the region is CLOSED, and the region cannot be CLOSED until the
> compaction is finished. *deadlock*
> The "obvious" fix is to avoid RegionServers from triggering system table
> migrations, but Sergey and [~elserj] both think that this will end badly
> (RegionServers falling over because they expect the tables to be migrated and
> they aren't).
> Thoughts? [~ankit.singhal], [~jamestaylor], any others?
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