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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3900) QJM: avoid validating log segments on log rolls
Date Fri, 07 Sep 2012 03:41:08 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3900?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13450304#comment-13450304
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Todd Lipcon commented on HDFS-3900:
-----------------------------------

should note: I wasn't able to easily write a unit test for this, but I verified that the log
rolls no longer validated the logs whereas edits synchronization did. This also sped up the
log roll timing significantly.
                
> QJM: avoid validating log segments on log rolls
> -----------------------------------------------
>
>                 Key: HDFS-3900
>                 URL: https://issues.apache.org/jira/browse/HDFS-3900
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>    Affects Versions: QuorumJournalManager (HDFS-3077)
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>         Attachments: hdfs-3900.txt
>
>
> Currently, we are paranoid and validate every log segment when it is finalized. For the
a log segment that has been written entirely by one writer, with no recovery in between, this
is overly paranoid (we don't do this for local journals). It also causes log rolls to be slow
and take time linear in the size of the segment. Instead, we should optimize this path to
simply trust that the segment is correct so long as the txids match up as expected.

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