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From "Arjen Roodselaar (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-10205) ConcurrentModificationException in BucketAllocator
Date Thu, 19 Dec 2013 22:03:09 GMT

    [ https://issues.apache.org/jira/browse/HBASE-10205?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13853372#comment-13853372
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Arjen Roodselaar commented on HBASE-10205:
------------------------------------------

I took the Chunhui's patch, but made some additional changes to allow parallelism in the BucketAllocator
on the BucketSizeInfo level. I think synchronization can be removed from BucketAllocator.allocateBlock()
and BucketAllocator.freeBlock(), but need to verify this under some stress. I will be running
a load test over the next 24 hours and report back.

> 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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