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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-297) Implement a pure Java CRC32 calculator
Date Wed, 08 Jul 2009 18:17:15 GMT

    [ https://issues.apache.org/jira/browse/HDFS-297?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12728835#action_12728835
] 

Todd Lipcon commented on HDFS-297:
----------------------------------

Dhruba: During testing I ran on many more iterations than just the 24. Whether it lives in
the unit test with more or less I don't have a big opinion on. Seems to me that it should
be fast enough that we can run a few thousand with no noticeable test performance degradation.

As for the code, I believe Scott wrote it with some guidance from some C source, but it's
definitely not ripped from another project - I googled far and wide for a good implementation
in Java and didn't find any that were this fast. I think we now have the fastest crc32 in
the west ;-)

> Implement a pure Java CRC32 calculator
> --------------------------------------
>
>                 Key: HDFS-297
>                 URL: https://issues.apache.org/jira/browse/HDFS-297
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Owen O'Malley
>            Assignee: Todd Lipcon
>         Attachments: crc32-results.txt, hadoop-5598-evil.txt, hadoop-5598-hybrid.txt,
hadoop-5598.txt, hadoop-5598.txt, hdfs-297.txt, PureJavaCrc32.java, PureJavaCrc32.java, PureJavaCrc32.java,
TestCrc32Performance.java, TestCrc32Performance.java, TestCrc32Performance.java, TestPureJavaCrc32.java
>
>
> We've seen a reducer writing 200MB to HDFS with replication = 1 spending a long time
in crc calculation. In particular, it was spending 5 seconds in crc calculation out of a total
of 6 for the write. I suspect that it is the java-jni border that is causing us grief.

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