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From "Jean-Daniel Cryans (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-5898) Consider double-checked locking for block cache lock
Date Wed, 31 Oct 2012 17:54:13 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5898?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13488011#comment-13488011
] 

Jean-Daniel Cryans commented on HBASE-5898:
-------------------------------------------

bq. The most likely explanation for the 2nd issue seems to be HDFS slowness

Improbable. With the patch, the first thread would try to get the block and get stuck, the
others would first try to read without the lock, fail, and then would also block. Except that
when I applied the patch it resolved the issue.
                
> 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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