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Date: Fri, 28 Dec 2007 17:19:43 -0800 (PST)
From: "Chris Kline (JIRA)" <jira@apache.org>
To: hadoop-dev@lucene.apache.org
Subject: [jira] Created: (HADOOP-2500) [HBase] Unreadable region kills
 region servers
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[HBase] Unreadable region kills region servers
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                 Key: HADOOP-2500
                 URL: https://issues.apache.org/jira/browse/HADOOP-2500
             Project: Hadoop
          Issue Type: Bug
          Components: contrib/hbase
         Environment: CentOS 5
            Reporter: Chris Kline


Backgound: The name node (also a DataNode and RegionServer) in our cluster ran out of disk space.  I created some space, restarted HDFS and fsck reported corruption with an HBase file.  I cleared up that corruption and restarted HBase.  I was still unable to read anything from HBase even though HSFS was now healthy.

The following was gather from the log files.  When HMaster starts up, it finds a region that is no good (Key: 17_125736271):
2007-12-24 09:07:14,342 DEBUG org.apache.hadoop.hbase.HMaster: Current assignment of spider_pages,17_125736271,1198286140018 is no good

HMaster then assigns this region to RegionServer X.60:
2007-12-24 09:07:17,126 INFO org.apache.hadoop.hbase.HMaster: assigning region spider_pages,17_125736271,1198286140018 to server 10.100.11.60:60020
2007-12-24 09:07:20,152 DEBUG org.apache.hadoop.hbase.HMaster: Received MSG_REPORT_PROCESS_OPEN : spider_pages,17_125736271,1198286140018 from 10.100.11.60:60020

The RegionServer has trouble reading that region (from the RegionServer log on X.60); Note that the worker thread exits
2007-12-24 09:07:22,611 DEBUG org.apache.hadoop.hbase.HStore: starting spider_pages,17_125736271,1198286140018/meta (2062710340/meta with reconstruction log: (/data/hbase1/hregion_2062710340/oldlogfile.log
2007-12-24 09:07:22,620 DEBUG org.apache.hadoop.hbase.HStore: maximum sequence id for hstore spider_pages,17_125736271,1198286140018/meta (2062710340/meta) is 4549496
2007-12-24 09:07:22,622 ERROR org.apache.hadoop.hbase.HRegionServer: error opening region spider_pages,17_125736271,1198286140018
java.io.EOFException
        at java.io.DataInputStream.readFully(DataInputStream.java:180)
        at java.io.DataInputStream.readFully(DataInputStream.java:152)
        at org.apache.hadoop.io.SequenceFile$Reader.init(SequenceFile.java:1383)
        at org.apache.hadoop.io.SequenceFile$Reader.<init>(SequenceFile.java:1360)
        at org.apache.hadoop.io.SequenceFile$Reader.<init>(SequenceFile.java:1349)
        at org.apache.hadoop.io.SequenceFile$Reader.<init>(SequenceFile.java:1344)
        at org.apache.hadoop.hbase.HStore.doReconstructionLog(HStore.java:697)
        at org.apache.hadoop.hbase.HStore.<init>(HStore.java:632)
        at org.apache.hadoop.hbase.HRegion.<init>(HRegion.java:288)
        at org.apache.hadoop.hbase.HRegionServer.openRegion(HRegionServer.java:1211)
        at org.apache.hadoop.hbase.HRegionServer$Worker.run(HRegionServer.java:1162)
        at java.lang.Thread.run(Thread.java:619)
2007-12-24 09:07:22,623 FATAL org.apache.hadoop.hbase.HRegionServer: Unhandled exception
java.lang.NullPointerException
        at org.apache.hadoop.hbase.HRegionServer.reportClose(HRegionServer.java:1095)
        at org.apache.hadoop.hbase.HRegionServer.openRegion(HRegionServer.java:1217)
        at org.apache.hadoop.hbase.HRegionServer$Worker.run(HRegionServer.java:1162)
        at java.lang.Thread.run(Thread.java:619)
2007-12-24 09:07:22,623 INFO org.apache.hadoop.hbase.HRegionServer: worker thread exiting

The HMaster then tries to assign the same region to X.60 again and fails.  The HMaster tries to assign the region to X.31 with the same result (X.31 worker thread exits).

The file it is complaining about, /data/hbase1/hregion_2062710340/oldlogfile.log, is a zero-length file in HDFS.  After deleting that file and restarting HBase, HBase appears to be back to normal.

One thing I can't figure out is that the HMaster log show several entries after the worker thread on X.60 has exited suggesting that the RegionServer is talking with HMaster:
2007-12-24 09:08:23,349 DEBUG org.apache.hadoop.hbase.HMaster: Received MSG_REPORT_PROCESS_OPEN : spider_pages,17_125736271,1198286140018 from 10.100.11.60:60020
2007-12-24 09:10:29,543 DEBUG org.apache.hadoop.hbase.HMaster: Received MSG_REPORT_PROCESS_OPEN : spider_pages,17_125736271,1198286140018 from 10.100.11.60:60020

There is no corresponding entry in the RegionServer's log.

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