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From "ramkrishna.s.vasudevan (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HBASE-15999) NPE in MemstoreCompactor
Date Wed, 15 Jun 2016 11:57:09 GMT

     [ https://issues.apache.org/jira/browse/HBASE-15999?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

ramkrishna.s.vasudevan updated HBASE-15999:
-------------------------------------------
    Attachment: HBASE-15999_4.patch

Updated patch. Thanks for pointing it out. My bad.

> NPE in MemstoreCompactor
> ------------------------
>
>                 Key: HBASE-15999
>                 URL: https://issues.apache.org/jira/browse/HBASE-15999
>             Project: HBase
>          Issue Type: Sub-task
>    Affects Versions: 2.0.0
>            Reporter: ramkrishna.s.vasudevan
>            Assignee: ramkrishna.s.vasudevan
>            Priority: Critical
>             Fix For: 2.0.0
>
>         Attachments: HBASE-15999.patch, HBASE-15999_1.patch, HBASE-15999_2.patch, HBASE-15999_3.patch,
HBASE-15999_4.patch
>
>
> In the INMEMORY_COMPACTION_POOL ThreadPoolExecutor for every thread the current thread
name is also appended. Since we are using a pool the name gets appended and we end up in names
like this
> {code}
> "B.defaultRpcServer.handler=89,queue=9,port=16041-inmemoryCompactions-1465492533442-inmemoryCompactions-1465492548754-inmemoryCompactions-1465492548913-inmemoryCompactions-1465492549625-inmemoryCompactions-1465492549956-inmemoryCompactions-1465492567040-inmemoryCompactions-1465492567160-inmemoryCompactions-1465492578465-inmemoryCompactions-1465492578707-inmemoryCompactions-1465492579292-inmemoryCompactions-1465492579357-inmemoryCompactions-1465492579786-inmemoryCompactions-1465492580059-inmemoryCompactions-1465492589975-inmemoryCompactions-1465492590192-inmemoryCompactions-1465492590484-inmemoryCompactions-1465492591144-inmemoryCompactions-1465492592603-inmemoryCompactions-1465492592799-inmemoryCompactions-1465492597106-inmemoryCompactions-1465492602925-inmemoryCompactions-1465492606620-inmemoryCompactions-1465492651478-inmemoryCompactions-1465492653460-inmemoryCompactions-1465492677020-inmemoryCompactions-1465492680857-inmemoryCompactions-1465492681989-inmemoryCompactions-1465492721818-inmemoryCompactions-1465492723562-inmemoryCompactions-1465492724801-inmemoryCompactions-1465492726665-inmemoryCompactions-1465492745750-inmemoryCompactions-1465492745964-inmemoryCompactions-1465492746578-inmemoryCompactions-1465492756867-inmemoryCompactions-1465492764727-inmemoryCompactions-1465492766944-inmemoryCompactions-1465492767098-inmemoryCompactions-1465492785298-inmemoryCompactions-1465492788334-inmemoryCompactions-1465492795954-inmemoryCompactions-1465493047265-inmemoryCompactions-1465493091530-inmemoryCompactions-1465493185684"
#6006 daemon prio=5 os_prio=0 tid=0x000000000daa6800 nid=0x454a runnable [0x00007f50fd0b9000]
> {code}
> As we were surprised to see why so many threads are getting created as Anoop pointed
out the pool size is 10 and there is no setting for the thread to die, the reason for this
issue is that we have an multi threaded issue in MemstoreCompactor. The memstoreCompactor
has the StoreScanner and MemstoreScanner as the state variable and every time we just instantiate
a new one when a new inmemory flush request comes. Finally we try to release the resource
where the scanner is nullified and closed. But the instance would have already been updated
or nullified by another thread when there are multiple requests. So this causes an NPE in
releaseResources.
> {code}
> Exception in thread "B.defaultRpcServer.handler=76,queue=6,port=16041-inmemoryCompactions-1465906554314"
java.lang.NullPointerException
>         at org.apache.hadoop.hbase.regionserver.MemStoreCompactor.releaseResources(MemStoreCompactor.java:108)
>         at org.apache.hadoop.hbase.regionserver.MemStoreCompactor.doCompaction(MemStoreCompactor.java:144)
>         at org.apache.hadoop.hbase.regionserver.MemStoreCompactor.startCompaction(MemStoreCompactor.java:88)
>         at org.apache.hadoop.hbase.regionserver.CompactingMemStore.flushInMemory(CompactingMemStore.java:287)
>         at org.apache.hadoop.hbase.regionserver.CompactingMemStore$InMemoryFlushRunnable.run(CompactingMemStore.java:356)
>         at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
>         at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
> {code}
> So every time the thread dies and a new is created which I found from the stack traces
by adding some logs. So this is why we were creating lot of threads and the name was simply
getting appened. Now from this we can see that adding the Handler name is fine but the main
issue is the NPE.



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