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https://issues.apache.org/jira/browse/HBASE-7728?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13567546#comment-13567546
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ramkrishna.s.vasudevan commented on HBASE-7728:
-----------------------------------------------

Yes  logs will be needed.  
If sync is still going on from cleanUpWriter then it means that this.writer is 
not null still.
If this.writer is not null then the IOE also should not have happened.

If sync has happened then syncedTillHere should have changed.  So nice thing to 
analyse and debug.
The updateLock is needed too while changing the writer.  


                
> 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
>
> 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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