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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-5898) Consider double-checked locking for block cache lock
Date Thu, 01 Nov 2012 05:29:16 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5898?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13488477#comment-13488477
] 

stack commented on HBASE-5898:
------------------------------

The offheap cache is being used by no one -- its unusable in current form -- and doubtful
anyone would ever use it or if it even makes sense to use it as currently implemented instead
of just having bigger block cache w/ decent GC tuning + file system cache instead.  I'd be
fine for ripping it out until someone wanted to take it up and finish it off.
                
> 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
>             Fix For: 0.94.3, 0.96.0
>
>         Attachments: 5898-TestBlocksRead.txt, HBASE-5898-0.patch, HBASE-5898-1.patch,
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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