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Date: Tue, 3 Nov 2009 21:19:34 +0000 (UTC)
From: "Todd Lipcon (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=12773199#action_12773199 ] 

Todd Lipcon commented on HADOOP-3205:
-------------------------------------

Looking at the source of BufferedInputStream (at http://www.docjar.com/html/api/java/io/BufferedInputStream.java.html) it actually seems like BufferedInputStream is already handling pass-through to the underlying stream in the case that the read buffer is as large as its own buffer. That was the crucial bit I was missing that explains why performing the underlying reads in larger chunks would make a difference, even without removing the BIS.

I'll give it a go and see if there is any discernible performance increase.

bq. Plus, looking at how long this jira has been open, it is no blocker

Of course :)

> 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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