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From "stack (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-5623) Race condition when rolling the HLog and hlogFlush
Date Fri, 23 Mar 2012 21:31:26 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5623?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13237157#comment-13237157
] 

stack commented on HBASE-5623:
------------------------------

Seems fine.  Edit your comments.  Does it pass the test?  Do you want to include the test?
  Do you think this will slow writes?  Should we check for null writer here: '+      return
this.writer.getLength();'

This seems like a catch that is very broad:

{code}
+      } catch (IOException io) {
+        // try again is lock held
{code}

Can we narrow it at all?  Would an NPE come up here?

This log message is going to freak out the chicken littles out there: '+          LOG.debug("Log
roll failed", io);'  Can you do some amelioration?  Something like, failed this time but we'll
be back soon to retry?
                
> Race condition when rolling the HLog and hlogFlush
> --------------------------------------------------
>
>                 Key: HBASE-5623
>                 URL: https://issues.apache.org/jira/browse/HBASE-5623
>             Project: HBase
>          Issue Type: Bug
>          Components: wal
>    Affects Versions: 0.94.0
>            Reporter: Enis Soztutar
>            Assignee: Enis Soztutar
>            Priority: Critical
>             Fix For: 0.94.0
>
>         Attachments: 5623.txt, 5623v2.txt, HBASE-5623_v0.patch
>
>
> When doing a ycsb test with a large number of handlers (regionserver.handler.count=60),
I get the following exceptions:
> {code}
> Caused by: org.apache.hadoop.ipc.RemoteException: java.io.IOException: java.lang.NullPointerException
> 	at org.apache.hadoop.io.SequenceFile$Writer.getLength(SequenceFile.java:1099)
> 	at org.apache.hadoop.hbase.regionserver.wal.SequenceFileLogWriter.getLength(SequenceFileLogWriter.java:314)
> 	at org.apache.hadoop.hbase.regionserver.wal.HLog.syncer(HLog.java:1291)
> 	at org.apache.hadoop.hbase.regionserver.wal.HLog.sync(HLog.java:1388)
> 	at org.apache.hadoop.hbase.regionserver.HRegion.doMiniBatchPut(HRegion.java:2192)
> 	at org.apache.hadoop.hbase.regionserver.HRegion.put(HRegion.java:1985)
> 	at org.apache.hadoop.hbase.regionserver.HRegionServer.multi(HRegionServer.java:3400)
> 	at sun.reflect.GeneratedMethodAccessor17.invoke(Unknown Source)
> 	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
> 	at java.lang.reflect.Method.invoke(Method.java:597)
> 	at org.apache.hadoop.hbase.ipc.WritableRpcEngine$Server.call(WritableRpcEngine.java:366)
> 	at org.apache.hadoop.hbase.ipc.HBaseServer$Handler.run(HBaseServer.java:1351)
> 	at org.apache.hadoop.hbase.ipc.HBaseClient.call(HBaseClient.java:920)
> 	at org.apache.hadoop.hbase.ipc.WritableRpcEngine$Invoker.invoke(WritableRpcEngine.java:152)
> 	at $Proxy1.multi(Unknown Source)
> 	at org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation$3$1.call(HConnectionManager.java:1691)
> 	at org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation$3$1.call(HConnectionManager.java:1689)
> 	at org.apache.hadoop.hbase.client.ServerCallable.withoutRetries(ServerCallable.java:214)
> {code}
> and 
> {code}
> 	java.lang.NullPointerException
> 		at org.apache.hadoop.io.SequenceFile$Writer.checkAndWriteSync(SequenceFile.java:1026)
> 		at org.apache.hadoop.io.SequenceFile$Writer.append(SequenceFile.java:1068)
> 		at org.apache.hadoop.io.SequenceFile$Writer.append(SequenceFile.java:1035)
> 		at org.apache.hadoop.hbase.regionserver.wal.SequenceFileLogWriter.append(SequenceFileLogWriter.java:279)
> 		at org.apache.hadoop.hbase.regionserver.wal.HLog$LogSyncer.hlogFlush(HLog.java:1237)
> 		at org.apache.hadoop.hbase.regionserver.wal.HLog.syncer(HLog.java:1271)
> 		at org.apache.hadoop.hbase.regionserver.wal.HLog.sync(HLog.java:1391)
> 		at org.apache.hadoop.hbase.regionserver.HRegion.doMiniBatchPut(HRegion.java:2192)
> 		at org.apache.hadoop.hbase.regionserver.HRegion.put(HRegion.java:1985)
> 		at org.apache.hadoop.hbase.regionserver.HRegionServer.multi(HRegionServer.java:3400)
> 		at sun.reflect.GeneratedMethodAccessor33.invoke(Unknown Source)
> 		at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
> 		at java.lang.reflect.Method.invoke(Method.java:597)
> 		at org.apache.hadoop.hbase.ipc.WritableRpcEngine$Server.call(WritableRpcEngine.java:366)
> 		at org.apache.hadoop.hbase.ipc.HBaseServer$Handler.run(HBaseServer.java:1351)
> {code}
> It seems the root cause of the issue is that we open a new log writer and close the old
one at HLog#rollWriter() holding the updateLock, but the other threads doing syncer() calls
> {code} 
> logSyncerThread.hlogFlush(this.writer);
> {code}
> without holding the updateLock. LogSyncer only synchronizes against concurrent appends
and flush(), but not on the passed writer, which can be closed already by rollWriter(). In
this case, since SequenceFile#Writer.close() sets it's out field as null, we get the NPE.


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