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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-3885) QJM: optimize log sync when JN is lagging behind
Date Sat, 01 Sep 2012 07:40:08 GMT
Todd Lipcon created HDFS-3885:

             Summary: 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

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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