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https://issues.apache.org/jira/browse/HBASE-8547?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13657786#comment-13657786
]
stack commented on HBASE-8547:
------------------------------
I forgot to say 'nice find' Enis.
Is it true to say that this can only happen when bottom half of a split is
looking for block at offset 0 -- first block -- or top-half of a split is
looking for last block in the file? If so, can this fact be exploited doing
block lookup or even catching the exception in these cases and letting it out
for any other?
Your unit test verifies half file has this issue?
Good on you Enis.
> Fix java.lang.RuntimeException: Cached an already cached block
> --------------------------------------------------------------
>
> Key: HBASE-8547
> URL: https://issues.apache.org/jira/browse/HBASE-8547
> Project: HBase
> Issue Type: Bug
> Components: io, regionserver
> Reporter: Enis Soztutar
> Assignee: Enis Soztutar
> Fix For: 0.98.0, 0.94.8, 0.95.1
>
> Attachments: hbase-8547_v1-0.94.patch, hbase-8547_v1-0.94.patch,
> hbase-8547_v1.patch, hbase-8547_v2-0.94-reduced.patch
>
>
> In one test, one of the region servers received the following on 0.94.
> Note HalfStoreFileReader in the stack trace. I think the root cause is that
> after the region is split, the mid point can be in the middle of the block
> (for store files that the mid point is not chosen from). Each half store file
> tries to load the half block and put it in the block cache. Since IdLock is
> instantiated per store file reader, they do not share the same IdLock
> instance, thus does not lock against each other effectively.
> {code}
> 2013-05-12 01:30:37,733 ERROR
> org.apache.hadoop.hbase.regionserver.HRegionServer:ยท
> java.lang.RuntimeException: Cached an already cached block
> at
> org.apache.hadoop.hbase.io.hfile.LruBlockCache.cacheBlock(LruBlockCache.java:279)
> at
> org.apache.hadoop.hbase.io.hfile.HFileReaderV2.readBlock(HFileReaderV2.java:353)
> at
> org.apache.hadoop.hbase.io.hfile.HFileBlockIndex$BlockIndexReader.loadDataBlockWithScanInfo(HFileBlockIndex.java:254)
> at
> org.apache.hadoop.hbase.io.hfile.HFileReaderV2$AbstractScannerV2.seekTo(HFileReaderV2.java:480)
> at
> org.apache.hadoop.hbase.io.hfile.HFileReaderV2$AbstractScannerV2.seekTo(HFileReaderV2.java:501)
> at
> org.apache.hadoop.hbase.io.HalfStoreFileReader$1.seekTo(HalfStoreFileReader.java:237)
> at
> org.apache.hadoop.hbase.regionserver.StoreFileScanner.seekAtOrAfter(StoreFileScanner.java:226)
> at
> org.apache.hadoop.hbase.regionserver.StoreFileScanner.seek(StoreFileScanner.java:145)
> at
> org.apache.hadoop.hbase.regionserver.StoreFileScanner.enforceSeek(StoreFileScanner.java:351)
> at
> org.apache.hadoop.hbase.regionserver.KeyValueHeap.pollRealKV(KeyValueHeap.java:354)
> at
> org.apache.hadoop.hbase.regionserver.KeyValueHeap.generalizedSeek(KeyValueHeap.java:312)
> at
> org.apache.hadoop.hbase.regionserver.KeyValueHeap.requestSeek(KeyValueHeap.java:277)
> at
> org.apache.hadoop.hbase.regionserver.StoreScanner.reseek(StoreScanner.java:543)
> at
> org.apache.hadoop.hbase.regionserver.StoreScanner.next(StoreScanner.java:411)
> at
> org.apache.hadoop.hbase.regionserver.KeyValueHeap.next(KeyValueHeap.java:143)
> at
> org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.populateResult(HRegion.java:3829)
> at
> org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.nextInternal(HRegion.java:3896)
> at
> org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.nextRaw(HRegion.java:3778)
> at
> org.apache.hadoop.hbase.regionserver.HRegion$RegionScannerImpl.nextRaw(HRegion.java:3770)
> at
> org.apache.hadoop.hbase.regionserver.HRegionServer.next(HRegionServer.java:2643)
> at sun.reflect.GeneratedMethodAccessor25.invoke(Unknown Source)
> at
> sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
> at java.lang.reflect.Method.invoke(Method.java:597)
> at
> org.apache.hadoop.hbase.ipc.SecureRpcEngine$Server.call(SecureRpcEngine.java:308)
> at
> org.apache.hadoop.hbase.ipc.HBaseServer$Handler.run(HBaseServer.java:1426)
> {code}
> I can see two possible fixes:
> # Allow this kind of rare cases in LruBlockCache by not throwing an
> exception.
> # Move the lock instances to upper layer (possibly in CacheConfig), and let
> half hfile readers share the same IdLock implementation.
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