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From "Andrew Purtell (JIRA)" <j...@apache.org>
Subject [jira] Created: (HBASE-1439) race between master and regionserver after missed heartbeat
Date Tue, 19 May 2009 18:46:45 GMT
race between master and regionserver after missed heartbeat
-----------------------------------------------------------

                 Key: HBASE-1439
                 URL: https://issues.apache.org/jira/browse/HBASE-1439
             Project: Hadoop HBase
          Issue Type: Bug
    Affects Versions: 0.19.1
         Environment: CentOS 5.2 x86_64, HBase 0.19.1, Hadoop 0.19.1
            Reporter: Andrew Purtell


Seen on one of our 0.19.1 clusters:

{code}
java.io.FileNotFoundException: File does not exist: hdfs://jdc2-atr-dc-2.atr.trendmicro.com:50000/data/hbase/log_10.3.134.207_1242286427894_60020/hlog.dat.1242528291898
 at org.apache.hadoop.hdfs.DistributedFileSystem.getFileStatus(DistributedFileSystem.java:415)
 at org.apache.hadoop.fs.FileSystem.getLength(FileSystem.java:679)
 at org.apache.hadoop.hbase.io.SequenceFile$Reader.<init>(SequenceFile.java:1431)
 at org.apache.hadoop.hbase.io.SequenceFile$Reader.<init>(SequenceFile.java:1426)
 at org.apache.hadoop.hbase.regionserver.HLog.splitLog(HLog.java:753)
 at org.apache.hadoop.hbase.regionserver.HLog.splitLog(HLog.java:716)
 at org.apache.hadoop.hbase.master.ProcessServerShutdown.process(ProcessServerShutdown.java:249)
 at org.apache.hadoop.hbase.master.HMaster.processToDoQueue(HMaster.java:442)
 at org.apache.hadoop.hbase.master.HMaster.run(HMaster.java:377)
2009-05-17 04:05:55,481 INFO org.apache.hadoop.hbase.master.RegionServerOperation: process
shutdown of server 10.3.134.207:60020: logSplit: false, rootRescanned: false, numberOfMetaRegions:
1, onlineMetaRegions.size(): 1
{code}

I do not have the region server log yet, but here is my conjecture:

Here, the write ahead log for 10.3.134.207 is missing in DFS: java.io.FileNotFoundException:
hdfs://jdc2-atr-dc-2.atr.trendmicro.com:50000/data/hbase/log_10.3.134.207_1242286427894_60020/hlog.dat.1242528291898
when the master tries to split it after declaring the region server crashed. There have been
recent trouble reports on this cluster that indicate severe memory stress, e.g. kernel panics
due to OOM. Based on that I think it is likely that the region server here missed a heartbeat
so the master declared it crashed and began to split the log. But, the log was then deleted
out from underneath the master's split thread. I think the region server was actually still
running but partially swapped out or the node was otherwise overloaded so it missed its heartbeat.
Then, when the region server came back after being swapped in, it realized it missed its heartbeat
and shut down, deleting the log as is normally done. 

Even if the above is not the actual cause in this case, I think the scenario is plausible.
What do you think?

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