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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 Fri, 19 Jan 2018 20:51:00 GMT

    [ https://issues.apache.org/jira/browse/PHOENIX-4537?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16332884#comment-16332884
] 

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

Are we saying that migration would happen before the first client connection? That's bad.
Can we change that? We send the client version along in MetaDataEndpointImpl calls. Perhaps
we could send it through our region observers if need be.

My preference would be to implement PHOENIX-4530 and get rid of clearTsOnDisabledIndexes as
it wouldn't be necessary ([~ankit@apache.org] excellent idea). We might need to start adding
secondary indexes to system tables, so I'd hate to have too many assumptions here.

> 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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