Todd Lipcon created HDFS-3885:
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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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