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From "Andrew Purtell (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-13291) Lift the scan ceiling
Date Thu, 26 Mar 2015 22:14:54 GMT

    [ https://issues.apache.org/jira/browse/HBASE-13291?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14382801#comment-14382801
] 

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

bq.  it fingers the HBB#_get again.
HBB is generated from something called Heap-X-Buffer.java.template when the JDK is built.
However, looks like _get for HBB is:
{code}
    byte _get(int i) {                          // package-private
        return hb[i];
    }
{code}
... a simple array access. You'd expect this along with a lot of comparator work if we're
scanning or skipping through a lot of cells in memory. I think the way to optimize this is
keep an index to cells in the blockcache, to eliminate the need to read a length, skip, read
a length, skip, read a length... 

> 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: 13291.inlining.txt, Screen Shot 2015-03-26 at 12.12.13 PM.png, q
(1).png, traces.7.svg, traces.filterall.svg, traces.nofilter.svg, traces.small2.svg, traces.smaller.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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