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From "James Taylor (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (PHOENIX-4537) RegionServer initiating compaction can trigger schema migration and deadlock the system
Date Tue, 23 Jan 2018 00:41:00 GMT

    [ https://issues.apache.org/jira/browse/PHOENIX-4537?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16335228#comment-16335228
] 

James Taylor commented on PHOENIX-4537:
---------------------------------------

[~sergey.soldatov] - good point. PHOENIX-4530  would just prevent one occurrence. Can we brainstorm
on what it'd take to ensure that this migration doesn't happen on a server connection? I'm
hoping it could use the same general mechanism - check the PhoenixConnection for this "special"
property and don't initiate the migration if it's set.

> 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
>            Assignee: Josh Elser
>            Priority: Critical
>             Fix For: 5.0.0, 4.14.0
>
>         Attachments: PHOENIX-4537.001.patch
>
>
> [~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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