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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-9087) Handlers being blocked during reads
Date Wed, 31 Jul 2013 18:15:50 GMT

    [ https://issues.apache.org/jira/browse/HBASE-9087?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13725531#comment-13725531
] 

Lars Hofhansl commented on HBASE-9087:
--------------------------------------

That's why you make sure to have at least as many handlers as CPU threads, and few more to
handle io waits.
Having way more threads than CPU threads and spindles is counter productive and you're better
off queuing request.
                
> Handlers being blocked during reads
> -----------------------------------
>
>                 Key: HBASE-9087
>                 URL: https://issues.apache.org/jira/browse/HBASE-9087
>             Project: HBase
>          Issue Type: Bug
>          Components: Performance
>    Affects Versions: 0.94.7, 0.95.1
>            Reporter: Pablo Medina
>            Assignee: Elliott Clark
>            Priority: Critical
>             Fix For: 0.98.0, 0.95.2, 0.94.11
>
>         Attachments: HBASE-9087-0.patch, HBASE-9087-1.patch
>
>
> I'm having a lot of handlers (90 - 300 aprox) being blocked when reading rows. They are
blocked during changedReaderObserver registration.
> Lars Hofhansl suggests to change the implementation of changedReaderObserver from CopyOnWriteList
to ConcurrentHashMap.
> Here is a stack trace: 
> "IPC Server handler 99 on 60020" daemon prio=10 tid=0x0000000041c84000 nid=0x2244 waiting
on condition [0x00007ff51fefd000]
>    java.lang.Thread.State: WAITING (parking)
>         at sun.misc.Unsafe.park(Native Method)
>         - parking to wait for  <0x00000000c5c13ae8> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
>         at java.util.concurrent.locks.LockSupport.park(LockSupport.java:156)
>         at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:811)
>         at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:842)
>         at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1178)
>         at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:186)
>         at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:262)
>         at java.util.concurrent.CopyOnWriteArrayList.addIfAbsent(CopyOnWriteArrayList.java:553)
>         at java.util.concurrent.CopyOnWriteArraySet.add(CopyOnWriteArraySet.java:221)
>         at org.apache.hadoop.hbase.regionserver.Store.addChangedReaderObserver(Store.java:1085)
>         at org.apache.hadoop.hbase.regionserver.StoreScanner.<init>(StoreScanner.java:138)
>         at org.apache.hadoop.hbase.regionserver.Store.getScanner(Store.java:2077)
>         at org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.<init>(HRegion.java:3755)
>         at org.apache.hadoop.hbase.regionserver.HRegion.instantiateRegionScanner(HRegion.java:1804)
>         at org.apache.hadoop.hbase.regionserver.HRegion.getScanner(HRegion.java:1796)
>         at org.apache.hadoop.hbase.regionserver.HRegion.getScanner(HRegion.java:1771)
>         at org.apache.hadoop.hbase.regionserver.HRegion.get(HRegion.java:4776)
>         at org.apache.hadoop.hbase.regionserver.HRegion.get(HRegion.java:4750)
>         at org.apache.hadoop.hbase.regionserver.HRegionServer.get(HRegionServer.java:2152)
>         at org.apache.hadoop.hbase.regionserver.HRegionServer.multi(HRegionServer.java:3700)
>         at sun.reflect.GeneratedMethodAccessor26.invoke(Unknown Source)
>         at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
>         at java.lang.reflect.Method.invoke(Method.java:597)
>         at org.apache.hadoop.hbase.ipc.WritableRpcEngine$Server.call(WritableRpcEngine.java:320)
>         at org.apache.hadoop.hbase.ipc.HBaseServer$Handler.run(HBaseServer.java:1426)
>       

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