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https://issues.apache.org/jira/browse/HDFS-3092?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13245475#comment-13245475
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Flavio Junqueira commented on HDFS-3092:
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Thanks for the responses, Suresh.
bq. For HDFS editlogs, my feeling is that there will only be three JDs. One on
the active namenode, second on the standby and a third JD on one of the
machines. In federation, one has to configure a JD per Federated namespace.
Alternative is to use BookKeeper, since it could make the deployment simpler
for federated large cluster.
When you say three JDs, that's the degree of replication, right? When I said
multiple logs, I was referring to multiple namenodes writing to different logs,
as with federation.
bq. I think the comment was more about comparing the design and complexity of
deployment and not benchmarks for two systems. Performance is not the
motivation for this jira.
Got it. You're thinking about a qualitative design based on the requirements
identified. Correctness sounds like an obvious candidate. :-)
bq. We decided on majority quorum to keep the design simple, though it is
strictly not necessary. A JD in JournalList is supposed to have all the entries
and any JD from the list can be used to read the journals.
I think my confusion here is that you require a quorum to be able to
acknowledge the operation, but in reality you try to write to everyone. If you
can't write to everyone, then you induce a view change (change to JournalList).
Is this right?
> 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: MultipleSharedJournals.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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