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https://issues.apache.org/jira/browse/HADOOP-5598?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12719232#action_12719232
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dhruba borthakur commented on HADOOP-5598:
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Looking at the results, it appears that a choice of Crc algorithms, crc data
sizes and JVMs can result in pretty varied performance numbers. Maybe it would
be worthwhile to make the ChecksymFilesystem pick a Checksum object based on a
config parameter.
Also, the hybrid model of dynamically deciding which algo to use (based on the
size of data to checksum) sounds a litle scary to me :-)
> Implement a pure Java CRC32 calculator
> --------------------------------------
>
> Key: HADOOP-5598
> URL: https://issues.apache.org/jira/browse/HADOOP-5598
> Project: Hadoop Core
> Issue Type: Improvement
> Components: dfs
> Reporter: Owen O'Malley
> Assignee: Todd Lipcon
> Attachments: crc32-results.txt, hadoop-5598-hybrid.txt,
> hadoop-5598.txt, TestCrc32Performance.java, TestCrc32Performance.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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