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From Ming Fang <mingf...@mac.com>
Subject Re: Prevent failback to MASTER after failover
Date Tue, 23 Apr 2013 21:40:14 GMT

It sounds like the solution is to set the constraints so that only one transition at a time.

Can you point me to an example of how to do this?
Also is this something I can set in the JSON file?

Sent from my iPad

On Apr 1, 2013, at 11:32 AM, kishore g <g.kishore@gmail.com> wrote:

> 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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