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Date: Thu, 14 Jul 2016 14:38:20 +0000 (UTC)
From: "Joshua McKenzie (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
Message-ID: <JIRA.12989264.1468447368000.28823.1468507100706@Atlassian.JIRA>
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Subject: [jira] [Commented] (CASSANDRA-12198) Deadlock in CDC during segment
 flush
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archived-at: Thu, 14 Jul 2016 14:38:22 -0000


    [ https://issues.apache.org/jira/browse/CASSANDRA-12198?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15377031#comment-15377031 ] 

Joshua McKenzie commented on CASSANDRA-12198:
---------------------------------------------

CI looks good - failures aren't related to this change. Committed to 3.8 branch, also to 3.9 then merged to trunk.

> Deadlock in CDC during segment flush
> ------------------------------------
>
>                 Key: CASSANDRA-12198
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-12198
>             Project: Cassandra
>          Issue Type: Bug
>            Reporter: Joshua McKenzie
>            Assignee: Joshua McKenzie
>            Priority: Blocker
>             Fix For: 3.8
>
>
> In the patch for CASSANDRA-8844, we added a {{synchronized(this)}} block inside CommitLogSegment.setCDCState. This introduces the possibility of deadlock in the following scenario:
> # A {{CommitLogSegment.sync()}} call is made (synchronized method)
> # A {{CommitLogSegment.allocate}} call from a cdc-enabled write is in flight and acquires a reference to the Group on appendOrder (the OpOrder in the Segment)
> # {{CommmitLogSegment.sync}} hits {{waitForModifications}} which calls {{appendOrder.awaitNewBarrier}}
> # The in-flight write, if changing the state of the segment from CDCState.PERMITTED to CDCState.CONTAINS, enters {{setCDCState}} and blocks on synchronized(this)
> And neither of them ever come back. This came up while doing some further work on CASSANDRA-12148.


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