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https://issues.apache.org/jira/browse/HADOOP-3205?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12774161#action_12774161
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Raghu Angadi commented on HADOOP-3205:
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> So, I think this is actually improving performance because of some other
> effect like better cache locality by operating in larger chunks. Admittedly,
> cache locality is always the fallback excuse for a performance increase, but
> I don't have a better explanation yet. Anyone care to hazard a guess?
hmm... avoiding a copy should save measurable CPU. I will run some experiments
as well.
> Read multiple chunks directly from FSInputChecker subclass into user buffers
> ----------------------------------------------------------------------------
>
> Key: HADOOP-3205
> URL: https://issues.apache.org/jira/browse/HADOOP-3205
> Project: Hadoop Common
> Issue Type: Bug
> Components: fs
> Reporter: Raghu Angadi
> Assignee: Todd Lipcon
> Attachments: hadoop-3205.txt, hadoop-3205.txt, hadoop-3205.txt
>
>
> Implementations of FSInputChecker and FSOutputSummer like DFS do not have
> access to full user buffer. At any time DFS can access only up to 512 bytes
> even though user usually reads with a much larger buffer (often controlled by
> io.file.buffer.size). This requires implementations to double buffer data if
> an implementation wants to read or write larger chunks of data from
> underlying storage.
> We could separate changes for FSInputChecker and FSOutputSummer into two
> separate jiras.
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