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From "Hairong Kuang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-928) make checksums optional per FileSystem
Date Tue, 27 Feb 2007 18:52:06 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-928?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12476306
] 

Hairong Kuang commented on HADOOP-928:
--------------------------------------

Yes, Doug. I think what you said about a small outer buffer and a big inner buffer makes sense.
Personally I feel that for checksumming, the idea buffer size should be bytesPerSum. But I
am not sure of the cost of data copying. After both this patch and the rack-aware performance
patch are committed, I plan to work on some benchmarks on file I/O. I will experiment with
two buffer size strategies then.

For the sum file buffer, I set its size to be the same as to the outer buffer. My intention
is to use the same buffer size to read both data and checksums. Another option is to set the
sum buffer size to be (outer buffer size/bytesPerSum), or as you suggested, set it to be the
default buffer size. Please let me know what you think.

I also checked ChecksumFileSystem#create. Yes, the data stream should use a small buffer size.
I will make the change.

> make checksums optional per FileSystem
> --------------------------------------
>
>                 Key: HADOOP-928
>                 URL: https://issues.apache.org/jira/browse/HADOOP-928
>             Project: Hadoop
>          Issue Type: Improvement
>          Components: fs
>            Reporter: Doug Cutting
>         Assigned To: Hairong Kuang
>         Attachments: checksum.patch, checksum1.patch, checksum2.patch
>
>
> Checksumming is currently built into the base FileSystem class.  It should instead be
optional, with each FileSystem implementation electing whether to use the Hadoop-provided
checksum system, or to disable it, or to implement its own custom checksum system.
> To implement this, a ChecksumFileSystem implementation can be provided that wraps another
FileSystem implementation, implementing checksums as in Hadoop's current mandatory implementation
(i.e., as a separate crc file per file that's elided from directory listings).  The 'raw'
FileSystem methods would be removed.  FSDataInputStream and FSDataOutputStream would be made
interfaces.

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