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From "Jean-Daniel Cryans (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2692) Master rewrite and cleanup for 0.90
Date Wed, 21 Jul 2010 21:15:52 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2692?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12890897#action_12890897

Jean-Daniel Cryans commented on HBASE-2692:

My first pass on the document, would be nice if the doc was on rb.

bq.      - Master startup determines whether this is startup or failover by counting the number
of RS nodes in ZK.

FWIW there's also a znode called "shutdown" that, if present, means that the cluster is up
and running.

bq.      - Master waits for the minimum number of RS to be available to be assigned regions.

I'd be interested to see your thoughts about determining the minimum number of RSs. Also how
do you handle the assignment of ROOT and META? What's the chance that there's always enough
RSs that reported in once both catalog regions are assigned?

    Periodically, and when there are not any regions in transition, a load
     balancer will run and move regions around to balance cluster load

It's not clear to me why you have to wait. Then you wrote:

bq.     - Load balancer blocks until there are no regions in transition.

So once the load balancer is started, do we block regions going in transition?

bq.      - Master sends RPCs to the source RSs, telling them to CLOSE the regions.

What happens if a region splits while load balancing is running?

bq.      - Master finds all regions of the table.

Same question, what do you do if a region splits just after that? Won't you be missing 2 regions
and giving a CLOSE rpc that's invalid?

> Master rewrite and cleanup for 0.90
> -----------------------------------
>                 Key: HBASE-2692
>                 URL: https://issues.apache.org/jira/browse/HBASE-2692
>             Project: HBase
>          Issue Type: Improvement
>            Reporter: Jonathan Gray
>            Assignee: Jonathan Gray
>            Priority: Blocker
>             Fix For: 0.90.0
>         Attachments: BRANCH_NOTES.txt
> This is the parent issue for master changes targeted at 0.90 release.
> Changes done as part of this issue grew out of work done over in HBASE-2485 to move region
transitions into ZK.
> In addition to that work, this issue will include general HMaster and ZooKeeper refactorings
and cleanups.

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