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From "Andrew Purtell (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-13291) Lift the scan ceiling
Date Fri, 20 Mar 2015 00:05:38 GMT

    [ https://issues.apache.org/jira/browse/HBASE-13291?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14370416#comment-14370416
] 

Andrew Purtell commented on HBASE-13291:
----------------------------------------

Those flame graphs show on-CPU differences. Would be really interesting to see where and how
long IO worker threads are waiting and how that differs among the two cases. 

I quick look over the nofilter and filterall graphs suggest that the filterall case removes
a lot of RPC work so shifts on-CPU processing from a mix of:
- RPC handling and related data copies
- skipping to desired cells (skipping through blocks in blockcache, and logic in SQM#match)

to mostly skipping to desired cells. We maybe could optimize this with an index into the blockcache
but the actual bottleneck may lie elsewhere with queueing/threading issues.

> Lift the scan ceiling
> ---------------------
>
>                 Key: HBASE-13291
>                 URL: https://issues.apache.org/jira/browse/HBASE-13291
>             Project: HBase
>          Issue Type: Improvement
>          Components: Scanners
>    Affects Versions: 1.0.0
>            Reporter: stack
>            Assignee: stack
>         Attachments: traces.filterall.svg, traces.nofilter.svg
>
>
> Scanning medium sized rows with multiple concurrent scanners exhibits interesting 'ceiling'
properties. A server runs at about 6.7k ops a second using 450% of possible 1600% of CPUs
 when 4 clients each with 10 threads doing scan 1000 rows.  If I add '--filterAll' argument
(do not return results), then we run at 1450% of possible 1600% possible but we do 8k ops
a second.
> Let me attach flame graphs for two cases. Unfortunately, there is some frustrating dark
art going on. Let me try figure it... Filing issue in meantime to keep score in.



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