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