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https://issues.apache.org/jira/browse/HDFS-6440?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14538749#comment-14538749
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Jesse Yates commented on HDFS-6440:
-----------------------------------
{quote}
Right, I get that, but what I was pointing out was just that in the previous
version of the patch the variable "ie" was never being assigned to anything but
"null".
{quote}
Oh, yeah. That was a problem. Sorry for the misunderstanding!
bq. I'm specifically thinking about just expanding TestRollingUpgrade with some
tests that exercise the > 2 NN scenario, e.g.
Yea, I'll look into that - look for it in the next patch. Shouldn't be too hard
(and might be cleaner codewise!)
{quote}
I get the point of using the random seed in the first place, but I'm
specifically talking about the fact that in doWriteOverFailoverTest we change
the value of that variable, log the value, and then never read it again.
{quote}
Well, we use it again through the random variable which will determine the ID
of the NN to become the ANN.
{code}
int nextActive = failoverRandom.nextInt(NN_COUNT);
{code}
By setting the seed, you get the same sequence nn failures. So one seed would
do 1->2->1->3, while another might do 1->3->2->1. Then, with the seed you could
reproduce the series of failovers in the same order, which seems like a
laudable goal for the test- especially when trying to debug weird error cases.
Unless I'm missing something?
> 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
> Fix For: 3.0.0
>
> Attachments: Multiple-Standby-NameNodes_V1.pdf,
> hdfs-6440-cdh-4.5-full.patch, hdfs-6440-trunk-v1.patch,
> hdfs-6440-trunk-v1.patch, hdfs-6440-trunk-v3.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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