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Date: Mon, 30 May 2011 06:02:47 +0000 (UTC)
From: "Min Zhou (JIRA)" <jira@apache.org>
To: common-issues@hadoop.apache.org
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Subject: [jira] [Updated] (HADOOP-7339) Introduce a buffered checksum for
 avoiding frequently calls on Checksum.update()
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     [ https://issues.apache.org/jira/browse/HADOOP-7339?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Min Zhou updated HADOOP-7339:
-----------------------------

    Attachment: HADOOP-7339-v2.diff

fixed svn conflicts.

> Introduce a buffered checksum for avoiding frequently calls on Checksum.update()
> --------------------------------------------------------------------------------
>
>                 Key: HADOOP-7339
>                 URL: https://issues.apache.org/jira/browse/HADOOP-7339
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: util
>            Reporter: Min Zhou
>             Fix For: 0.22.0
>
>         Attachments: HADOOP-7339-v1.diff, HADOOP-7339-v2.diff
>
>
> We found that PureJavaCRC32/CRC32.update() is the TOP 1 of the methods consuming CPU in a map side, and in reduce side, it cost a lots of CPU too.
> IFileOutputStream would frequently call Checksum.update() during writing a record. It's very common a MR key/value less than 512 bytes. Checksum.update() would be called every time writing a key/value. 
> Test case: terasort 100MB. 
> Checksum.update() calls has be reduced from 4030348 to 28069.  This method is not a hotspot anymore.

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