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https://issues.apache.org/jira/browse/HDFS-6440?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14275579#comment-14275579
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Jesse Yates commented on HDFS-6440:
-----------------------------------
thanks for the comments. I'll work on a new version, but in the meantime, some
responses:
bq. StandbyCheckpointer#activeNNAddresses
The standby checkpointer doesn't necessarily run just on the SNN - it could be
in multiple places. Further, I think you are presupposing that there is only
one SNN and one ANN; since there will commonly be at least 3 NNs, any one of
the two other NNs could be the active NN. I could see it being renamed as
potentialActiveNNAddresses, but I don't think that gains that much more clarity
for the increased verbosity.
bq. I saw you removed {final}
I was trying to keep in the spirit of the original mini-cluster code. The final
safety concern is really only necessary in this case when you are changing the
number of configured NNs and then accessing them in different threads; I have
no idea when that would even make sense. Even then you wouldn't have been
thread-safe in the original code as it there is no locking on the array of NNs.
I removed the finals to keep the same style as the original wrt to changing the
topology.
bq. Are the changes in 'log4j.properties' necessary?
Not strictly, but its just the test log4j properties (so no effect on the
production version) and just adds more debugging information, in this case,
which thread is actually making the log message.
I'll update the others
> Support more than 2 NameNodes
> -----------------------------
>
> Key: HDFS-6440
> URL: https://issues.apache.org/jira/browse/HDFS-6440
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: auto-failover, ha, namenode
> Affects Versions: 2.4.0
> Reporter: Jesse Yates
> Assignee: Jesse Yates
> Attachments: Multiple-Standby-NameNodes_V1.pdf,
> hdfs-6440-cdh-4.5-full.patch, hdfs-6440-trunk-v1.patch,
> hdfs-multiple-snn-trunk-v0.patch
>
>
> Most of the work is already done to support more than 2 NameNodes (one
> active, one standby). This would be the last bit to support running multiple
> _standby_ NameNodes; one of the standbys should be available for fail-over.
> Mostly, this is a matter of updating how we parse configurations, some
> complexity around managing the checkpointing, and updating a whole lot of
> tests.
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