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https://issues.apache.org/jira/browse/HBASE-1107?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12682084#action_12682084
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stack commented on HBASE-1107:
------------------------------
The code in updateReaders was changed significantly for 0.19.1 (We don't open
readers we already had open).
The NPE above as Andrew has already pointed out comes from here:
{code}
// I think its safe getting key from mem at this stage -- it
shouldn't have
// been flushed yet
this.scanners[HSFS_INDEX] = new StoreFileScanner(this.store,
this.timestamp, this. targetCols, this.keys[MEMS_INDEX].getRow());
{code}
It looks like its the this.keys[MEMS_INDEX] is null.
In testing while doing the 0.19.1 changes I was able to make this NPE. It
happened when updateReaders was called after the both memory and the file
scanners had been exhausted but the scanner had not yet been closed down fully.
The attempt to get from the memory key was failing because it had been set to
null after its last next.
Now, we keep the last next key and use that instead of trying to go to memcache
(thinking on it, memcache exhaustion can always happen ahead of store file
scanner exhaustion).
> NPE in HStoreScanner.updateReaders
> ----------------------------------
>
> Key: HBASE-1107
> URL: https://issues.apache.org/jira/browse/HBASE-1107
> Project: Hadoop HBase
> Issue Type: Bug
> Affects Versions: 0.19.1, 0.20.0
> Reporter: Andrew Purtell
> Assignee: Andrew Purtell
> Priority: Blocker
> Attachments: 1107-1.patch
>
>
> 2009-01-01 23:55:41,629 FATAL
> org.apache.hadoop.hbase.regionserver.MemcacheFlusher: Replay of hlog
> required. Forcing server shutdown
> org.apache.hadoop.hbase.DroppedSnapshotException: region:
> content,cff13605e2ea6ce0b221ac864687bf08,1230777531253
> at
> org.apache.hadoop.hbase.regionserver.HRegion.internalFlushcache(HRegion.java:880)
> at
> org.apache.hadoop.hbase.regionserver.HRegion.flushcache(HRegion.java:773)
> at
> org.apache.hadoop.hbase.regionserver.MemcacheFlusher.flushRegion(MemcacheFlusher.java:227)
> at
> org.apache.hadoop.hbase.regionserver.MemcacheFlusher.run(MemcacheFlusher.java:137)
> Caused by: java.lang.NullPointerException
> at
> org.apache.hadoop.hbase.regionserver.HStoreScanner.updateReaders(HStoreScanner.java:322)
> at
> org.apache.hadoop.hbase.regionserver.HStore.notifyChangedReadersObservers(HStore.java:737)
> at
> org.apache.hadoop.hbase.regionserver.HStore.updateReaders(HStore.java:725)
> at
> org.apache.hadoop.hbase.regionserver.HStore.internalFlushCache(HStore.java:694)
> at
> org.apache.hadoop.hbase.regionserver.HStore.flushCache(HStore.java:630)
> at
> org.apache.hadoop.hbase.regionserver.HRegion.internalFlushcache(HRegion.java:865)
> ... 3 more
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