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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-7728) deadlock occurs between hlog roller and hlog syncer
Date Fri, 01 Feb 2013 20:54:14 GMT

    [ https://issues.apache.org/jira/browse/HBASE-7728?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13569069#comment-13569069
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Lars Hofhansl commented on HBASE-7728:
--------------------------------------

That is why we should not change that. What I am saying is that if you access the writer inside
the updatalock in syncer() it will not be null.
If we set it to null when closing, we might expose us to other NPEs in other parts of the
code. As seen from this issue, this code is finicky.

That main point I am making is that the deadlock (this issues) is fixed by your reordering
of the locks (nice change, btw), and that the null stuff in an extraneous change.
We can add the null set/check to 0.96, for 0.94 I would prefer the minimum change possible
(unless you really feel strongly about this).

                
> deadlock occurs between hlog roller and hlog syncer
> ---------------------------------------------------
>
>                 Key: HBASE-7728
>                 URL: https://issues.apache.org/jira/browse/HBASE-7728
>             Project: HBase
>          Issue Type: Bug
>          Components: wal
>    Affects Versions: 0.94.2
>         Environment: Linux 2.6.18-164.el5 x86_64 GNU/Linux
>            Reporter: Wang Qiang
>            Assignee: Ted Yu
>            Priority: Blocker
>             Fix For: 0.96.0, 0.94.5
>
>         Attachments: 7728-0.94.txt, 7728-0.94-v2.txt, 7728-suggest-0.96.txt, 7728-suggest.txt,
7728-v1.txt, 7728-v2.txt, 7728-v3.txt, 7728-v4.txt
>
>
> the hlog roller thread and hlog syncer thread may occur dead lock with the 'flushLock'
and 'updateLock', and then cause all 'IPC Server handler' thread blocked on hlog append. the
jstack info is as follow :
> "regionserver60020.logRoller":
>         at org.apache.hadoop.hbase.regionserver.wal.HLog.syncer(HLog.java:1305)
>         - waiting to lock <0x000000067bf88d58> (a java.lang.Object)
>         at org.apache.hadoop.hbase.regionserver.wal.HLog.syncer(HLog.java:1283)
>         at org.apache.hadoop.hbase.regionserver.wal.HLog.sync(HLog.java:1456)
>         at org.apache.hadoop.hbase.regionserver.wal.HLog.cleanupCurrentWriter(HLog.java:876)
>         at org.apache.hadoop.hbase.regionserver.wal.HLog.rollWriter(HLog.java:657)
>         - locked <0x000000067d54ace0> (a java.lang.Object)
>         at org.apache.hadoop.hbase.regionserver.LogRoller.run(LogRoller.java:94)
>         at java.lang.Thread.run(Thread.java:662)
> "regionserver60020.logSyncer":
>         at org.apache.hadoop.hbase.regionserver.wal.HLog.syncer(HLog.java:1314)
>         - waiting to lock <0x000000067d54ace0> (a java.lang.Object)
>         - locked <0x000000067bf88d58> (a java.lang.Object)
>         at org.apache.hadoop.hbase.regionserver.wal.HLog.syncer(HLog.java:1283)
>         at org.apache.hadoop.hbase.regionserver.wal.HLog.sync(HLog.java:1456)
>         at org.apache.hadoop.hbase.regionserver.wal.HLog$LogSyncer.run(HLog.java:1235)
>         at java.lang.Thread.run(Thread.java:662)

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