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https://issues.apache.org/jira/browse/HBASE-5344?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13208103#comment-13208103
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Phabricator commented on HBASE-5344:
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stack has commented on the revision "[jira] [HBASE-5344] [89-fb] Scan
unassigned region directory on master failover".
Thanks for the explaination Mikhail. Let me tag along as a reviewer so I can
follow whats going on and so can help w/ the forward port.
"We have a plan to move towards always having the full assignment in ZK (the
UNASSIGNED directory will change its meaning then) to help guarantee that we
never have a duplicate assignment and to have only one source of truth for
assignment."
So, the '/unassigned' dir will change to be named '/regions' or some such?
On region open, we'll update its state in zk to be OPENED? And leave it there
(and update .META. too). We don't really need .META. then? Smile.
"We would like to rely on ZK and (for now) on META instead to recover the
region assignment on master startup/failure." The hard part in here is on
failover, what if the .META. is on a crashed server? You'll need to process
its logs and get .META. back online before you can proceed w/ failover. To get
it online, you'll need to listen for events (though I suppose you could filter
and only process .META. events). Or what if the the server carrrying .META.
crashes during onlining.
"Also, by the way, we are planning to unify master startup on a fresh cluster
start and failover and everything in between, and use the same logic to build a
coherent picture of region assignment."
Sweet.
REVISION DETAIL
https://reviews.facebook.net/D1605
> [89-fb] Scan unassigned region directory on master failover
> -----------------------------------------------------------
>
> Key: HBASE-5344
> URL: https://issues.apache.org/jira/browse/HBASE-5344
> Project: HBase
> Issue Type: Bug
> Reporter: Mikhail Bautin
> Assignee: Mikhail Bautin
> Attachments: D1605.1.patch
>
>
> In case the master dies after a regionserver writes region state as OPENED or
> CLOSED in ZK but before the update is received by master and written to meta,
> the new master that comes up has to pick up the region state from ZK and
> write it to meta. Otherwise we can get multiply-assigned regions.
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