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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-5898) Consider double-checked locking for block cache lock
Date Tue, 13 Nov 2012 04:09:17 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5898?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13495919#comment-13495919
] 

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

The repeat is a bit strange but it is at least easy to follow what is going on in this block
getting code so +1 on commit for 0.94.  No harm in beefing up this comment on commit:

{code}
+   * @param repeat Whether this is a repeat lookup for the same block
+   *        {@see HFileReaderV2#readBlock(long, long, boolean, boolean, boolean, BlockType)}
{code}

You refer to the code responsible for this 'repeat' param but maybe make mention of not wanting
to double-count metrics when doing double-check locking in the cited code?

Good on you Lars.
                
> 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, 5898-v2.txt, 5898-v3.txt, 5898-v4.txt,
HBASE-5898-0.patch, HBASE-5898-1.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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