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From "Kanak Biscuitwala (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HELIX-522) Support dynamic config by Helix
Date Sun, 28 Sep 2014 05:15:33 GMT

    [ https://issues.apache.org/jira/browse/HELIX-522?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14150975#comment-14150975
] 

Kanak Biscuitwala commented on HELIX-522:
-----------------------------------------

I think if we keep it at version management and let someone else decide what those versions
mean, that is probably sufficient and avoids the slippery slope.

A question I have is, what happens during a bounce of a node? Previously, we had a well-defined
initial state that the node would start in, and further, a node that comes up is assumed to
have not been assigned anything yet (and is thus in that initial state for all partitions).
To maintain this property, we would need to define some transition that's like (partition,
nothing) --> (partition, state, version), which is kind of like a 2D --> 3D transition,
and that's fine, but it's worth keeping in mind since it doesn't follow the same pattern as
other transitions.

> Support dynamic config by Helix
> -------------------------------
>
>                 Key: HELIX-522
>                 URL: https://issues.apache.org/jira/browse/HELIX-522
>             Project: Apache Helix
>          Issue Type: New Feature
>            Reporter: Zhen Zhang
>
> We are seeing a couple of use cases where an online service may need to roll out a set
of new configs in a coordinated way without bouncing the service. Helix can be extended to
support this. The basic idea is to generalize ideal-state to support multi-dimensional mappings.
Currently Helix uses ideal-state to define the target mapping from a partition to the placement
and state of the partition (i.e. partition->(placement, state). The mapping can be extended
to support another attribute, say config-version, so it would be partition->(placement,
state, config-version). Helix controller is then able to bring the system to the target mappings
in a coordinated way. Here is a high level design for this:
> https://cwiki.apache.org/confluence/display/HELIX/Support+Dynamic+Config



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