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https://issues.apache.org/jira/browse/HBASE-6603?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13438304#comment-13438304
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Enis Soztutar commented on HBASE-6603:
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Great find. Can we merge to 0.92 as well.
> RegionMetricsStorage.incrNumericMetric is called too often
> ----------------------------------------------------------
>
> Key: HBASE-6603
> URL: https://issues.apache.org/jira/browse/HBASE-6603
> Project: HBase
> Issue Type: Bug
> Components: performance
> Reporter: Lars Hofhansl
> Assignee: M. Chen
> Fix For: 0.96.0, 0.94.2
>
> Attachments: 6503-0.96.txt
>
>
> Running an HBase scan load through the profiler revealed that
> RegionMetricsStorage.incrNumericMetric is called way too often.
> It turns out that we make this call for *each* KV in StoreScanner.next(...).
> Incrementing AtomicLong requires expensive memory barriers.
> The observation here is that StoreScanner.next(...) can maintain a simple
> long in its internal loop and only update the metric upon exit. Thus the
> AtomicLong is not updated nearly as often.
> That cuts about 10% runtime from scan only load (I'll quantify this better
> soon).
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