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From kishore g <g.kish...@gmail.com>
Subject Re: Prevent failback to MASTER after failover
Date Mon, 01 Apr 2013 15:32:37 GMT
Hi Ming,

Thanks for the detailed explanation. Actually 5 & 6  happen in parallel,
Helix tries to parallelize the transitions as much as possible.

There is another feature in Helix that allows you to sort the transitions
based on some priority.See STATE_TRANSITION_PRIORITY_LIST in state model
definition. But after sorting Helix will send as many as possible in
parallel without violating constraints.

In your case you want the priority to be S-M, O-S, M-S but that is not
sufficient since O-S and M-S will be sent in parallel.

Additionally, what you need to do is set contraint on transition that there
should be only one transition per partition at any time. This will
basically make the order 6 5 7 and they will be executed sequentially per
partition.

We will try this  out and let you know, you dont need to change any code in
Helix or your app. You should be able to tweak the configuration
dynamically.

We will try to think of solving this in a more elegant way. I will file a
jira and add more info.

I also want to ask this question, when a node comes up if it is mandatory
to talk to MASTER what happens when the nodes are started for the first
time or when all nodes crash and come back.

thanks,
Kishore G

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