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https://issues.apache.org/jira/browse/HBASE-16616?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15713580#comment-15713580
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Tomu Tsuruhara commented on HBASE-16616:
----------------------------------------

Actually, a patch here was not enough to resolve the issue because of the same 
reason mentioned here 
https://issues.apache.org/jira/browse/HBASE-17072?focusedCommentId=15675394&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-15675394

HBASE-16146 seems more essential. It removes {{ThreadLocal}} usage from 
{[Counter}} entirely.

> Rpc handlers stuck on ThreadLocalMap.expungeStaleEntry
> ------------------------------------------------------
>
>                 Key: HBASE-16616
>                 URL: https://issues.apache.org/jira/browse/HBASE-16616
>             Project: HBase
>          Issue Type: Improvement
>          Components: Performance
>    Affects Versions: 1.2.2
>            Reporter: Tomu Tsuruhara
>            Assignee: Tomu Tsuruhara
>             Fix For: 2.0.0, 1.4.0
>
>         Attachments: 16616.branch-1.v2.txt, HBASE-16616.master.001.patch, 
> HBASE-16616.master.002.patch, ScreenShot 2016-09-09 14.17.53.png
>
>
> In our HBase 1.2.2 cluster, some regionserver showed too bad 
> "QueueCallTime_99th_percentile" exceeding 10 seconds.
> Most rpc handler threads stuck on ThreadLocalMap.expungeStaleEntry call at 
> that time.
> {noformat}
> "PriorityRpcServer.handler=18,queue=0,port=16020" #322 daemon prio=5 
> os_prio=0 tid=0x00007fd422062800 nid=0x19b89 runnable [0x00007fcb8a821000]
>    java.lang.Thread.State: RUNNABLE
>         at 
> java.lang.ThreadLocal$ThreadLocalMap.expungeStaleEntry(ThreadLocal.java:617)
>         at java.lang.ThreadLocal$ThreadLocalMap.remove(ThreadLocal.java:499)
>         at 
> java.lang.ThreadLocal$ThreadLocalMap.access$200(ThreadLocal.java:298)
>         at java.lang.ThreadLocal.remove(ThreadLocal.java:222)
>         at 
> java.util.concurrent.locks.ReentrantReadWriteLock$Sync.tryReleaseShared(ReentrantReadWriteLock.java:426)
>         at 
> java.util.concurrent.locks.AbstractQueuedSynchronizer.releaseShared(AbstractQueuedSynchronizer.java:1341)
>         at 
> java.util.concurrent.locks.ReentrantReadWriteLock$ReadLock.unlock(ReentrantReadWriteLock.java:881)
>         at 
> com.yammer.metrics.stats.ExponentiallyDecayingSample.unlockForRegularUsage(ExponentiallyDecayingSample.java:196)
>         at 
> com.yammer.metrics.stats.ExponentiallyDecayingSample.update(ExponentiallyDecayingSample.java:113)
>         at 
> com.yammer.metrics.stats.ExponentiallyDecayingSample.update(ExponentiallyDecayingSample.java:81)
>         at 
> org.apache.hadoop.metrics2.lib.MutableHistogram.add(MutableHistogram.java:81)
>         at 
> org.apache.hadoop.metrics2.lib.MutableRangeHistogram.add(MutableRangeHistogram.java:59)
>         at 
> org.apache.hadoop.hbase.ipc.MetricsHBaseServerSourceImpl.dequeuedCall(MetricsHBaseServerSourceImpl.java:194)
>         at 
> org.apache.hadoop.hbase.ipc.MetricsHBaseServer.dequeuedCall(MetricsHBaseServer.java:76)
>         at org.apache.hadoop.hbase.ipc.RpcServer.call(RpcServer.java:2192)
>         at org.apache.hadoop.hbase.ipc.CallRunner.run(CallRunner.java:112)
>         at 
> org.apache.hadoop.hbase.ipc.RpcExecutor.consumerLoop(RpcExecutor.java:133)
>         at org.apache.hadoop.hbase.ipc.RpcExecutor$1.run(RpcExecutor.java:108)
>         at java.lang.Thread.run(Thread.java:745)
> {noformat}
> We were using jdk 1.8.0_92 and here is a snippet from ThreadLocal.java.
> {code}
> 616:    while (tab[h] != null)
> 617:        h = nextIndex(h, len);
> {code}
> So I hypothesized that there're too many consecutive entries in {{tab}} array 
> and actually I found them in the heapdump.
> !ScreenShot 2016-09-09 14.17.53.png|width=50%!
> Most of these entries pointed at instance of 
> {{org.apache.hadoop.hbase.util.Counter$1}}
> which is equivarent to {{indexHolderThreadLocal}} instance-variable in the 
> {{Counter}} class.
> Because {{RpcServer$Connection}} class creates a {{Counter}} instance 
> {{rpcCount}} for every connections,
> it is possible to have lots of {{Counter#indexHolderThreadLocal}} instances 
> in RegionServer process
> when we repeat connect-and-close from client. As a result, a ThreadLocalMap 
> can have lots of consecutive
> entires.
> Usually, since each entry is a {{WeakReference}}, these entries are collected 
> and removed
> by garbage-collector soon after connection closed.
> But if connection's life-time was long enough to survive youngGC, it wouldn't 
> be collected until old-gen collector runs.
> Furthermore, under G1GC deployment, it is possible not to be collected even 
> by old-gen GC(mixed GC)
> if entries sit in a region which doesn't have much garbages.
> Actually we used G1GC when we encountered this problem.
> We should remove the entry from ThreadLocalMap by calling ThreadLocal#remove 
> explicitly.



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