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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-5898) Consider double-checked locking for block cache lock
Date Sat, 27 Oct 2012 03:47:14 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5898?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13485341#comment-13485341
] 

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

[~lhofhansl] When you say different scenarios, are you thinking a.) Todd saw contention on
this lock and made a workaround -- this is what this issue addresses -- meanwhile the other
scenario b.), is what JD and a few of us saw that looked like weird jvm-bug-like slowness
in this same area and this patch works around that issue (Ram saw slowness too)?  I'm a little
worried that after this patch goes in, b.) will still happen but will just be harder to trip.
 Would be coolio if could reproduce and poke at it. 
                
> 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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