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From "Kihwal Lee (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2080) Speed up DFS read path
Date Mon, 20 Jun 2011 17:32:48 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2080?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13052090#comment-13052090

Kihwal Lee commented on HDFS-2080:

This is awesome! I will review the patch carefully, but I have a couple of questions for now.

* Did you compare the performance of "software" version with zlib? Just to make sure we fallback
to a better one. If zlib's crc32 doesn't perform significantly better, using what we have
will be simpler for supporting different polynomials.

* I did a bit of experiment about filling up the pipeline. When there is no data dependency,
I get 1.17 cycles/Qword. By dividing the buffer into three chunks, I get about 1.6 - 1.7 cycles/Qword.
This is before combining results and processing remainder.  I didn't tweak too much, so it
might be possible to make it a bit better.  Although it's not in the patch, I am sure you
have play with it. Is there anything you found useful in making this work?

> Speed up DFS read path
> ----------------------
>                 Key: HDFS-2080
>                 URL: https://issues.apache.org/jira/browse/HDFS-2080
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs client
>    Affects Versions: 0.23.0
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>             Fix For: 0.23.0
>         Attachments: hdfs-2080.txt
> I've developed a series of patches that speeds up the HDFS read path by a factor of about
2.5x (~300M/sec to ~800M/sec for localhost reading from buffer cache) and also will make it
easier to allow for advanced users (eg hbase) to skip a buffer copy. 

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