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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, 08 May 2012 20:33:49 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5898?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13270801#comment-13270801
] 

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

Can you do a test where much lower hit ratio?  Any way to compare the amount of 'work' done
by the cache or how latency is effected?  I'm wondering if you can use your tool to simulate
the below:

{quote}
The downside is that for a workload with a lower cache hit ratio, we'll ask the cache twice
for every cache miss instead of just once. So we should see what the performance difference
is for something like a 10MB cache with 1GB dataset, where the dataset fits in the OS buffer
cache.
{quote}

If you can't, is it something you should make it measure?
                
> 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
>         Attachments: 5898-TestBlocksRead.txt, 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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