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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-5598) Implement a pure Java CRC32 calculator
Date Sat, 20 Jun 2009 04:00:07 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-5598?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12722132#action_12722132
] 

Todd Lipcon commented on HADOOP-5598:
-------------------------------------

Thanks, Owen. I definitely see your point about the JNI code possibly locking or copying.
The API we're using says it tries to avoid doing that when possible, but I guess for large
blocks, heap fragmentation is quite likely and we'd run into that issue.

I'm going on vacation this next week, so I'm unlikely to work on it, but if you have a moment
to upload your implementation for comparison I'll be back on this the week after next.

> Implement a pure Java CRC32 calculator
> --------------------------------------
>
>                 Key: HADOOP-5598
>                 URL: https://issues.apache.org/jira/browse/HADOOP-5598
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: dfs
>            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, 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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