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Date: Thu, 11 Mar 2010 19:30:29 +0000 (UTC)
From: "Jay Booth (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Subject: [jira] Commented: (HDFS-1034) Enhance datanode to read data and
 checksum file in parallel
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    [ https://issues.apache.org/jira/browse/HDFS-1034?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12844186#action_12844186 ] 

Jay Booth commented on HDFS-1034:
---------------------------------

Wouldn't this preclude the use of transferTo for transfer from the main block file?  The packet header and sums need to be sent before transferTo is invoked, otherwise things would all be jumbled up together.

> Enhance datanode to read data and checksum file in parallel
> -----------------------------------------------------------
>
>                 Key: HDFS-1034
>                 URL: https://issues.apache.org/jira/browse/HDFS-1034
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>
> In the current HDFS implementation, a read of a block issued to the datanode results in a disk access to the checksum file followed by a disk access to the checksum file. It would be nice to be able to do these two IOs in parallel to reduce read latency.

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