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From "Scott Carey (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-5598) Implement a pure Java CRC32 calculator
Date Thu, 18 Jun 2009 17:42:07 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-5598?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Scott Carey updated HADOOP-5598:
--------------------------------

    Attachment: PureJavaCrc32.java

This version does some algebraic manipulation and gets to about 10% faster than the native
implementation on large blocks on my machine (Java 1.6, mac osx, 64 bit, 2.5Ghz Core2 duo).

pure java	16MB block:   397.516 MB/sec
sun native 16MB block:  337.731 MB/sec

This version uses the same lookup table as the previous, occupying 1KB.

I have another pure java version that uses four lookup tables (4KB) that I will be posting
shortly after I clean it up.

Its results for large blocks are:

pure java	16MB block:   624.390 MB/sec
sun native 16MB block:  342.246 MB/sec

it first breaks 600MB/sec at a block size of 128 bytes and is over 520MB/sec at a block size
of 32 bytes.


A big remaining question is performance under concurrency.  The larger lookup table footprint
may bring this version down a little.
Any version calling out to native code may also slow under concurrency.



> 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-evil.txt, hadoop-5598-hybrid.txt,
hadoop-5598.txt, hadoop-5598.txt, PureJavaCrc32.java, PureJavaCrc32.java, 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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