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https://issues.apache.org/jira/browse/HBASE-7728?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13568429#comment-13568429
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Anoop Sam John commented on HBASE-7728:
---------------------------------------

Ted
synchronized (this.updateLock) {
             // HBASE-4387, HBASE-5623, retry with updateLock held
             tempWriter = this.writer;
-            logSyncerThread.hlogFlush(tempWriter, pending);
           }
Here also the syncer thread is trying to get the updateLock and holding the 
flushLock.
Same time roller thread holds the updateLock and it tries to get the flushLock.
This is what happened in the issue.  So will this remove the deadlock?

A log would greatly help us if there is some thing. Any chance [~aaronwq]
                
> 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
>            Priority: Blocker
>             Fix For: 0.96.0, 0.94.5
>
>         Attachments: 7728-suggest-0.96.txt, 7728-suggest.txt, 7728-v1.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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