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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1034) Enhance datanode to read data and checksum file in parallel
Date Thu, 11 Mar 2010 23:26:27 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1034?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12844270#action_12844270
] 

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

Only scary thing about moving checksums to a different mountpoint is that the checksum file's
metadata will be on a different journal than the data files. This might end up fine, but it's
a little nervewracking in terms of what kind of consistency we get out of the FS - could cause
some very subtle bugs.

Have we seen these issues to be a significant bottleneck?

> 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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