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List:       hadoop-dev
Subject:    [jira] [Created] (HADOOP-7339) Introduce a buffered checksum for
From:       "Min Zhou (JIRA)" <jira () apache ! org>
Date:       2011-05-30 5:26:47
Message-ID: 888908724.52741.1306733207354.JavaMail.tomcat () hel ! zones ! apache ! org
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Introduce a buffered checksum for avoiding frequently calls on Checksum.update()
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                 Key: HADOOP-7339
                 URL: https://issues.apache.org/jira/browse/HADOOP-7339
             Project: Hadoop Common
          Issue Type: Improvement
          Components: util
            Reporter: Min Zhou


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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