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From "Yves Langisch (Created) (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-5171) Potential NullPointerException while obtaining row lock
Date Tue, 10 Jan 2012 16:27:39 GMT
Potential NullPointerException while obtaining row lock 
--------------------------------------------------------

                 Key: HBASE-5171
                 URL: https://issues.apache.org/jira/browse/HBASE-5171
             Project: HBase
          Issue Type: Bug
          Components: regionserver
    Affects Versions: 0.90.5
            Reporter: Yves Langisch


We have a table which is concurrently accessed (read/write) from many threads and we make
use of row locks. Under heavy load we regularly get NPE while obtaining row locks. An example
stack trace looks as follows:

java.lang.NullPointerException
      at org.apache.hadoop.hbase.regionserver.HRegionServer.convertThrowableToIOE(HRegionServer.java:986)
      at org.apache.hadoop.hbase.regionserver.HRegionServer.lockRow(HRegionServer.java:2008)
      at sun.reflect.GeneratedMethodAccessor20.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.HBaseRPC$Server.call(HBaseRPC.java:570)
      at org.apache.hadoop.hbase.ipc.HBaseServer$Handler.run(HBaseServer.java:1039)
Caused by: java.lang.NullPointerException
      at java.util.concurrent.ConcurrentHashMap.put(ConcurrentHashMap.java:881)
      at org.apache.hadoop.hbase.regionserver.HRegionServer.addRowLock(HRegionServer.java:2018)
      at org.apache.hadoop.hbase.regionserver.HRegionServer.lockRow(HRegionServer.java:2004)
      ... 5 more 

After checking the source code I've noticed that the value which is going to be put into the
HashMap can be null in the case where the waitForLock flag is true or the rowLockWaitDuration
is expired (HRegion#internalObtainRowLock, line 2111ff). The latter I think happens in our
case as we have heavy load hitting the server.

IMHO this case should be handled somehow and must not lead to a NPE.

-
Yves

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