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From "Aaron T. Myers (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3885) QJM: optimize log sync when JN is lagging behind
Date Fri, 07 Sep 2012 21:48:07 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3885?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13451023#comment-13451023

Aaron T. Myers commented on HDFS-3885:

+1, patch looks great, and the testing you did sounds good.
> QJM: optimize log sync when JN is lagging behind
> ------------------------------------------------
>                 Key: HDFS-3885
>                 URL: https://issues.apache.org/jira/browse/HDFS-3885
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>    Affects Versions: QuorumJournalManager (HDFS-3077)
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>         Attachments: hdfs-3885.txt
> This is a potential optimization that we can add to the JournalNode: when one of the
nodes is lagging behind the others (eg because its local disk is slower or there was a network
blip), it receives edits after they've been committed to a majority. It can tell this because
the committed txid included in the request info is higher than the highest txid in the actual
batch to be written. In this case, we know that this batch has already been fsynced to a quorum
of nodes, so we can skip the fsync() on the laggy node, helping it to catch back up.

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