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https://issues.apache.org/jira/browse/HDFS-4960?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13701670#comment-13701670
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stack commented on HDFS-4960:
-----------------------------
+1 on patch. When you run w/ it [~varunsharma], do you no longer see the
7-byte extra seek? All unit tests passing would seem to say you haven't broken
anything. Missing I suppose is a test that shows we do not touch the .meta
file at all when skip checksum is enabled (else it'd have turned up the issue
you uncovered here).
> 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: Bug
> Affects Versions: 3.0.0, 2.1.0-beta
> Reporter: Varun Sharma
> Assignee: 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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