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https://issues.apache.org/jira/browse/HBASE-10205?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13853636#comment-13853636
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chunhui shen commented on HBASE-10205:
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I think the contention on the BucketAllocator won't be the bottleneck of
writer threads.
AllocateBlock() are only triggerd after we miss the block from cache and get
block from HDFS,
In that case, IOPS is the bottleneck of system.
> 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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