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Date: Thu, 11 Mar 2010 20:56:27 +0000 (UTC)
From: "Todd Lipcon (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=12844232#action_12844232 ] 

Todd Lipcon commented on HDFS-1034:
-----------------------------------

A bit of manual readahead on the checksum file could theoretically have the same benefit without the problem Jay mentioned. The Checksum file is opened with a buffer, right? In that case, do we expect to see a big benefit?

> 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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