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From "ramkrishna.s.vasudevan (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-6900) RegionScanner.reseek() creates NPE when a flush or compaction happens before the reseek.
Date Sat, 29 Sep 2012 11:36:07 GMT

    [ https://issues.apache.org/jira/browse/HBASE-6900?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13466187#comment-13466187
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ramkrishna.s.vasudevan commented on HBASE-6900:
-----------------------------------------------

{code}
2012-09-29 17:02:10,765 INFO  [main] regionserver.HStore(1045): Completed major compaction
of 1 file(s) in family of testToShowNPEOnRegionScannerReseek,,1348918329648.73944279562b7d512a9f318cc90098d2.
into 279f1073e9ba4e6db93d93eab86258cf, size=782.0; total size for store is 782.0
java.lang.NullPointerException
	at org.apache.hadoop.hbase.regionserver.StoreScanner.reseek(StoreScanner.java:569)
	at org.apache.hadoop.hbase.regionserver.NonLazyKeyValueScanner.doRealSeek(NonLazyKeyValueScanner.java:55)
	at org.apache.hadoop.hbase.regionserver.NonLazyKeyValueScanner.requestSeek(NonLazyKeyValueScanner.java:39)
	at org.apache.hadoop.hbase.regionserver.KeyValueHeap.generalizedSeek(KeyValueHeap.java:319)
	at org.apache.hadoop.hbase.regionserver.KeyValueHeap.requestSeek(KeyValueHeap.java:278)
	at org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.reseek(HRegion.java:3588)
	at org.apache.hadoop.hbase.regionserver.TestHRegion.testToShowNPEOnRegionScannerReseek(TestHRegion.java:232)
{code}
                
> RegionScanner.reseek() creates NPE when a flush or compaction happens before the reseek.
> ----------------------------------------------------------------------------------------
>
>                 Key: HBASE-6900
>                 URL: https://issues.apache.org/jira/browse/HBASE-6900
>             Project: HBase
>          Issue Type: Bug
>            Reporter: ramkrishna.s.vasudevan
>            Assignee: ramkrishna.s.vasudevan
>         Attachments: HBASE-6900.patch
>
>
> HBASE-5520 introduced reseek() on the RegionScanner.  
> Now when a scanner is created we have the StoreScanner heap.  After this if a flush or
compaction happens parallely all the StoreScannerObservers are cleared so that whenever a
new next() call happens we tend to recreate the scanner based on the latest store files.
> The reseek() in StoreScanner expects the heap not to be null because always reseek would
be called from next()
> {code}
> public synchronized boolean reseek(KeyValue kv) throws IOException {
>     //Heap cannot be null, because this is only called from next() which
>     //guarantees that heap will never be null before this call.
>     if (explicitColumnQuery && lazySeekEnabledGlobally) {
>       return heap.requestSeek(kv, true, useRowColBloom);
>     } else {
>       return heap.reseek(kv);
>     }
>   }
> {code}
> Now when we call RegionScanner.reseek() directly using CPs we tend to get a NPE.  In
our case it happened when a major compaction was going on.  I will also attach a testcase
to show the problem.

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