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https://issues.apache.org/jira/browse/HDFS-3885?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13450085#comment-13450085
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Todd Lipcon commented on HDFS-3885:
-----------------------------------
Another good idea, Chao.
I'm going to quickly implement the simpler idea described in the "description"
field of this JIRA, since it's trivial to do so. We can then open another JIRA
to actually aggregate larger batches "in the queue" to avoid the round trip
times.
> 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
>
> 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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