[HBASE-5623] Race condition when rolling the HLog and hlogFlush

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 0.94.0
• Fix Version/s: 0.94.0
• Component/s: wal
• Hadoop Flags: Reviewed
• Assignee: Enis Soztutar
• Reporter: Enis Soztutar
• Created: 23/Mar/12 01:22
• Updated: 12/Oct/12 05:35
• Resolved: 26/Mar/12 20:43

Description

When doing a ycsb test with a large number of handlers (regionserver.handler.count=60), I get the following exceptions:

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)

and

	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)

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

 
logSyncerThread.hlogFlush(this.writer);

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.

Issue Links

• relates to: HBASE-5336 Spurious exceptions in HConnectionImplementation