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https://issues.apache.org/jira/browse/HBASE-5898?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13488011#comment-13488011
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Jean-Daniel Cryans commented on HBASE-5898:
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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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