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https://issues.apache.org/jira/browse/HBASE-5898?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13272716#comment-13272716
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Todd Lipcon commented on HBASE-5898:
------------------------------------

Yep, I agree we need to fix the metrics messup before this is a candidate for 
commit.

I like the idea of moving the metric updates out.
                
> Consider double-checked locking for block cache lock
> ----------------------------------------------------
>
>                 Key: HBASE-5898
>                 URL: https://issues.apache.org/jira/browse/HBASE-5898
>             Project: HBase
>          Issue Type: Improvement
>          Components: performance
>    Affects Versions: 0.94.1
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>            Priority: Critical
>         Attachments: 5898-TestBlocksRead.txt, hbase-5898.txt
>
>
> Running a workload with a high query rate against a dataset that fits in 
> cache, I saw a lot of CPU being used in IdLock.getLockEntry, being called by 
> HFileReaderV2.readBlock. Even though it was all cache hits, it was wasting a 
> lot of CPU doing lock management here. I wrote a quick patch to switch to a 
> double-checked locking and it improved throughput substantially for this 
> workload.

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