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From "chunhui shen (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-10205) ConcurrentModificationException in BucketAllocator
Date Fri, 20 Dec 2013 01:54:07 GMT

    [ https://issues.apache.org/jira/browse/HBASE-10205?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13853585#comment-13853585
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chunhui shen commented on HBASE-10205:
--------------------------------------

[~arjenroodselaar]
As my understand to remove the synchronization from BucketAllocator.allocateBlock() and BucketAllocator.freeBlock(),
we should add synchronization for BucketSizeInfo#allocateBlock and BucketSizeInfo#findAndRemoveCompletelyFreeBucket,
it may cause dead lock.

Another solution is catch the ConcurrentModificationException and take a retry since it happens
occasionally


> ConcurrentModificationException in BucketAllocator
> --------------------------------------------------
>
>                 Key: HBASE-10205
>                 URL: https://issues.apache.org/jira/browse/HBASE-10205
>             Project: HBase
>          Issue Type: Bug
>          Components: regionserver
>    Affects Versions: 0.89-fb
>            Reporter: Arjen Roodselaar
>            Assignee: Arjen Roodselaar
>            Priority: Minor
>             Fix For: 0.89-fb, 0.99.0
>
>         Attachments: hbase-10205-trunk.patch
>
>
> The BucketCache WriterThread calls BucketCache.freeSpace() upon draining the RAM queue
containing entries to be cached. freeSpace() in turn calls BucketSizeInfo.statistics() through
BucketAllocator.getIndexStatistics(), which iterates over 'bucketList'. At the same time another
WriterThread might call BucketAllocator.allocateBlock(), which may call BucketSizeInfo.allocateBlock(),
add a bucket to 'bucketList' and consequently cause a ConcurrentModificationException. Calls
to BucketAllocator.allocateBlock() are synchronized, but calls to BucketAllocator.getIndexStatistics()
are not, which allows this race to occur.



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