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Date: Tue, 3 Nov 2009 21:07:32 +0000 (UTC)
From: "Raghu Angadi (JIRA)" <jira@apache.org>
To: common-issues@hadoop.apache.org
Subject: [jira] Commented: (HADOOP-3205) FSInputChecker and FSOutputSummer
 should allow better access to user buffer
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    [ https://issues.apache.org/jira/browse/HADOOP-3205?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12773193#action_12773193 ] 

Raghu Angadi commented on HADOOP-3205:
--------------------------------------

Also, as Hong's blog post points out, there are copies at many places. Advantage of improving the interface is not just avoiding one copy, but could eventually support better handling of direct buffers. 

Plus, looking at how long this jira has been open, it is no blocker :-)

> FSInputChecker and FSOutputSummer should allow better access to user buffer
> ---------------------------------------------------------------------------
>
>                 Key: HADOOP-3205
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3205
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: fs
>            Reporter: Raghu Angadi
>            Assignee: Raghu Angadi
>
> 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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