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From "Varun Sharma (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-4960) Unnecessary .meta seeks even when skip checksum is true
Date Sun, 07 Jul 2013 16:37:48 GMT

     [ https://issues.apache.org/jira/browse/HDFS-4960?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Varun Sharma updated HDFS-4960:

    Attachment: 4960-branch2.patch
> Unnecessary .meta seeks even when skip checksum is true
> -------------------------------------------------------
>                 Key: HDFS-4960
>                 URL: https://issues.apache.org/jira/browse/HDFS-4960
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>    Affects Versions: 3.0.0, 2.1.0-beta
>            Reporter: Varun Sharma
>         Attachments: 4960-branch2.patch, 4960-trunk.patch
> While attempting to benchmark an HBase + Hadoop 2.0 setup on SSDs, we found unnecessary
seeks into .meta files, each seek was a 7 byte read at the head of the file - this attempts
to validate the version #. Since the client is requesting no-checksum, we should not be needing
to touch the .meta file at all.
> Since the purpose of skip checksum is to also avoid the performance penalty of the extra
seek, we should not be seeking into .meta if skip checksum is true

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