Stopping a HRegionServer with unflushed cache causes data loss from org.apache.hadoop.hbase.DroppedSnapshotException

1. Start a Hbase cluster
2. Create a table t1: create 't1',

3. Put a cell in the table: put 't1', 'r1', 'f1:', 'value'
4. Scan it, see it's fine
5. Stop the HRegionSever hosting the t1 region: hbase/bin/hbase-daemon.sh stop regionserver.
6. Watch the region being reassigned from the original HRegionServer
7. Scan the t1 table again. It's empty now.

If between step 4 and step 5 the cache is flushed (e.g. Hbase cluster restart) no data is loss. However it means that if you stop a region server with dirty cache you will loose some data.

HRegionServer log after issuing hbase-daemon.sh stop regionserver:

2008-12-09 06:37:46,873 INFO org.apache.hadoop.ipc.Server: IPC Server handler 7 on 60020: exiting
2008-12-09 06:37:46,873 INFO org.apache.hadoop.ipc.Server: IPC Server handler 8 on 60020: exiting
2008-12-09 06:37:46,873 INFO org.apache.hadoop.ipc.Server: IPC Server handler 9 on 60020: exiting
2008-12-09 06:37:46,873 INFO org.apache.hadoop.ipc.Server: IPC Server handler 0 on 60020: exiting
2008-12-09 06:37:46,874 INFO org.apache.hadoop.hbase.regionserver.HRegionServer: Stopping infoServer
2008-12-09 06:37:46,874 INFO org.apache.hadoop.ipc.Server: Stopping IPC Server Responder
2008-12-09 06:37:46,874 INFO org.mortbay.util.ThreadedServer: Stopping Acceptor ServerSocket[addr=0.0.0.0/0.0.0.0,port=0,localport=60030]
2008-12-09 06:37:46,886 INFO org.mortbay.http.SocketListener: Stopped SocketListener on 0.0.0.0:60030
2008-12-09 06:37:46,948 INFO org.mortbay.util.Container: Stopped HttpContext[/static,/static]
2008-12-09 06:37:47,007 INFO org.mortbay.util.Container: Stopped HttpContext[/logs,/logs]
2008-12-09 06:37:47,007 INFO org.mortbay.util.Container: Stopped org.mortbay.jetty.servlet.WebApplicationHandler@60ded0f0
2008-12-09 06:37:47,094 INFO org.mortbay.util.Container: Stopped WebApplicationContext[/,/]
2008-12-09 06:37:47,094 INFO org.mortbay.util.Container: Stopped org.mortbay.jetty.Server@6490832e
2008-12-09 06:37:47,094 DEBUG org.apache.hadoop.hbase.regionserver.HRegionServer: closing region t1,,1228833363456
2008-12-09 06:37:47,094 DEBUG org.apache.hadoop.hbase.regionserver.HRegion: Compactions and cache flushes disabled for region t1,,1228833363456
2008-12-09 06:37:47,094 DEBUG org.apache.hadoop.hbase.regionserver.HRegion: Scanners disabled for region t1,,1228833363456
2008-12-09 06:37:47,094 DEBUG org.apache.hadoop.hbase.regionserver.HRegion: No more active scanners for region t1,,1228833363456
2008-12-09 06:37:47,095 DEBUG org.apache.hadoop.hbase.regionserver.HRegion: Updates disabled for region t1,,1228833363456
2008-12-09 06:37:47,095 DEBUG org.apache.hadoop.hbase.regionserver.HRegion: No more row locks outstanding on region t1,,1228833363456
2008-12-09 06:37:47,095 DEBUG org.apache.hadoop.hbase.regionserver.HRegion: Started memcache flush for region t1,,1228833363456. Current region memcache size 18.0
2008-12-09 06:37:47,095 INFO org.apache.hadoop.hbase.regionserver.Flusher: regionserver/0:0:0:0:0:0:0:0:60020.cacheFlusher exiting
2008-12-09 06:37:47,096 INFO org.apache.hadoop.hbase.regionserver.LogRoller: LogRoller exiting.
2008-12-09 06:37:47,096 INFO org.apache.hadoop.hbase.regionserver.CompactSplitThread: regionserver/0:0:0:0:0:0:0:0:60020.compactor exiting
2008-12-09 06:37:47,099 ERROR org.apache.hadoop.hbase.regionserver.HRegionServer: error closing region t1,,1228833363456
org.apache.hadoop.hbase.DroppedSnapshotException: region: t1,,1228833363456
at org.apache.hadoop.hbase.regionserver.HRegion.internalFlushcache(HRegion.java:1071)
at org.apache.hadoop.hbase.regionserver.HRegion.close(HRegion.java:619)
at org.apache.hadoop.hbase.regionserver.HRegionServer.closeAllRegions(HRegionServer.java:951)
at org.apache.hadoop.hbase.regionserver.HRegionServer.run(HRegionServer.java:459)
at java.lang.Thread.run(Thread.java:619)
Caused by: java.io.IOException: Filesystem closed
at org.apache.hadoop.dfs.DFSClient.checkOpen(DFSClient.java:196)
at org.apache.hadoop.dfs.DFSClient.getFileInfo(DFSClient.java:564)
at org.apache.hadoop.dfs.DistributedFileSystem.getFileStatus(DistributedFileSystem.java:390)
at org.apache.hadoop.fs.FileSystem.exists(FileSystem.java:667)
at org.apache.hadoop.hbase.regionserver.HStoreFile.<init>(HStoreFile.java:152)
at org.apache.hadoop.hbase.regionserver.HStore.internalFlushCache(HStore.java:599)
at org.apache.hadoop.hbase.regionserver.HStore.flushCache(HStore.java:577)
at org.apache.hadoop.hbase.regionserver.HRegion.internalFlushcache(HRegion.java:1058)
... 4 more
2008-12-09 06:37:47,100 DEBUG org.apache.hadoop.hbase.regionserver.HLog: closing log writer in hdfs://h1:54310/hbase/log_10.131.237.51_1228833326838_60020
2008-12-09 06:37:47,101 ERROR org.apache.hadoop.hbase.regionserver.HRegionServer: Close and delete failed
java.io.IOException: Filesystem closed
at org.apache.hadoop.dfs.DFSClient.checkOpen(DFSClient.java:196)
at org.apache.hadoop.dfs.DFSClient.access$600(DFSClient.java:59)
at org.apache.hadoop.dfs.DFSClient$DFSOutputStream.closeInternal(DFSClient.java:2689)
at org.apache.hadoop.dfs.DFSClient$DFSOutputStream.close(DFSClient.java:2655)
at org.apache.hadoop.fs.FSDataOutputStream$PositionCache.close(FSDataOutputStream.java:59)
at org.apache.hadoop.fs.FSDataOutputStream.close(FSDataOutputStream.java:79)
at org.apache.hadoop.io.SequenceFile$Writer.close(SequenceFile.java:962)
at org.apache.hadoop.hbase.regionserver.HLog.close(HLog.java:349)
at org.apache.hadoop.hbase.regionserver.HLog.closeAndDelete(HLog.java:333)
at org.apache.hadoop.hbase.regionserver.HRegionServer.run(HRegionServer.java:461)
at java.lang.Thread.run(Thread.java:619)
2008-12-09 06:37:47,102 INFO org.apache.hadoop.hbase.regionserver.HRegionServer: telling master that region server is shutting down at: 10.131.237.51:60020
2008-12-09 06:37:47,104 INFO org.apache.hadoop.hbase.regionserver.HRegionServer: stopping server at: 10.131.237.51:60020
2008-12-09 06:37:47,882 INFO org.apache.hadoop.hbase.Leases: regionserver/0:0:0:0:0:0:0:0:60020.leaseChecker closing leases
2008-12-09 06:37:47,882 INFO org.apache.hadoop.hbase.Leases: regionserver/0:0:0:0:0:0:0:0:60020.leaseChecker closed leases
2008-12-09 06:37:54,919 INFO org.apache.hadoop.hbase.regionserver.HRegionServer: worker thread exiting
2008-12-09 06:37:54,920 INFO org.apache.hadoop.hbase.regionserver.HRegionServer: regionserver/0:0:0:0:0:0:0:0:60020 exiting
2008-12-09 06:37:54,920 INFO org.apache.hadoop.hbase.regionserver.HRegionServer: Shutdown thread complete