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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-6621) Reduce calls to Bytes.toInt
Date Tue, 21 Aug 2012 03:34:38 GMT

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Todd Lipcon commented on HBASE-6621:
------------------------------------

Do you have benchmark results showing an improvement in actual scan speed?

When I looked into scan performance with oprofile a few months back, I found the same as you
-- that a lot of time was spent in these calls. But when I also added cache miss counters
to the profile, I found the reason was cache misses, not the actual CPU usage of the function.
So caching them would just shift around the cache miss to the next access of the cache line
elsewhere, without actually improving total performance.
                
> Reduce calls to Bytes.toInt
> ---------------------------
>
>                 Key: HBASE-6621
>                 URL: https://issues.apache.org/jira/browse/HBASE-6621
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Lars Hofhansl
>            Assignee: Lars Hofhansl
>            Priority: Minor
>             Fix For: 0.96.0, 0.94.2
>
>         Attachments: 6621-0.96.txt, 6621-0.96-v2.txt, 6621-0.96-v3.txt, 6621-0.96-v4.txt
>
>
> Bytes.toInt shows up quite often in a profiler run.
> It turns out that one source is HFileReaderV2$ScannerV2.getKeyValue().
> Notice that we call the KeyValue(byte[], int) constructor, which forces the constructor
to determine its size by reading some of the header information and calculate the size. In
this case, however, we already know the size (from the call to readKeyValueLen), so we could
just use that.
> In the extreme case of 10000's of columns this noticeably reduces CPU. 

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