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https://issues.apache.org/jira/browse/HBASE-5898?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13529517#comment-13529517
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Lars Hofhansl commented on HBASE-5898:
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I tracked it down to locking on istream in HFileBlock.readAtOffset.
Here's my test case: 20m rows, single column family, single column, blockcache
disabled for the scan, all data fits into the OS buffer cache.
Full scan over all rows.
One client scanning: 15s (regionserver keeps one core busy ~120%)
Two clients scanning along the same set of blocks: They both time out.
(regionserver is a 5-6% CPU, clearly just waiting)
Then I changed readAtOffset to always do preads. Now:
One client scanning: 39s (regionserver at ~120%)
Two clients scanning: 39s each (regionserver at ~210%)
So not sure how to proceed. Generally switching to pread obviously does not
work (scan time almost tripled).
seek + read does not scale to multiple threads. I *bet* this is the issue folks
have been seeing and this patch does not address that.
> 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: 5898-0.94.txt, 5898-TestBlocksRead.txt, 5898-v2.txt,
> 5898-v3.txt, 5898-v4.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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