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