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https://issues.apache.org/jira/browse/HDFS-3092?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13272101#comment-13272101
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Eli Collins commented on HDFS-3092:
-----------------------------------
Specifically, in HDFS-3092 we "write in parallel to all active/syncing
journals. Writes must complete on all active journals or fail/timeout."
therefore the latency of a transaction is that of the slowest JD. Note that the
write must complete - a JD can't ack a write that's not on disk. In 3077 the
latency is the slowest of the JDs in a quorum (ie if you have 5 JDs the latency
is that of the 3rd fastest JD).
> Enable journal protocol based editlog streaming for standby namenode
> --------------------------------------------------------------------
>
> Key: HDFS-3092
> URL: https://issues.apache.org/jira/browse/HDFS-3092
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: ha, name-node
> Affects Versions: 0.24.0, 0.23.3
> Reporter: Suresh Srinivas
> Assignee: Suresh Srinivas
> Attachments: ComparisonofApproachesforHAJournals.pdf, JNStates.png,
> MultipleSharedJournals.pdf, MultipleSharedJournals.pdf,
> MultipleSharedJournals.pdf, Removingfilerdependency.pdf
>
>
> Currently standby namenode relies on reading shared editlogs to stay current
> with the active namenode, for namespace changes. BackupNode used streaming
> edits from active namenode for doing the same. This jira is to explore using
> journal protocol based editlog streams for the standby namenode. A daemon in
> standby will get the editlogs from the active and write it to local edits. To
> begin with, the existing standby mechanism of reading from a file, will
> continue to be used, instead of from shared edits, from the local edits.
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