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Date: Fri, 26 Oct 2012 06:27:14 +0000 (UTC)
From: "stack (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
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Subject: [jira] [Commented] (HBASE-5898) Consider double-checked locking for
 block cache lock
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    [ https://issues.apache.org/jira/browse/HBASE-5898?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13484739#comment-13484739 ] 

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

[~ram_krish] How you mean Ram?  It was stuck where in particular?  Was it a bunch of threads getting same block?  What did the thread dump look like?  There is some issue in here around the wait/notify it seems as implemented.  The double-checked is probably better anyways but could the issue come back just less frequently after this patch goes in?
                
> 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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