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https://issues.apache.org/jira/browse/HBASE-16616?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15484210#comment-15484210
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Ted Yu commented on HBASE-16616:
--------------------------------
+1
> 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
> Attachments: HBASE-16616.master.001.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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