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From "Matthieu Morel (JIRA)" <>
Subject [jira] [Commented] (S4-110) Enhance cluster management features in S4
Date Thu, 10 Jan 2013 16:44:13 GMT


Matthieu Morel commented on S4-110:

There is a patch in branch S4-110. Currently commit [9661f27].

In my opinion, it would be better to have both helix and legacy cluster management available
for 0.6

Here is a list of notes about the integration:
* InstanceConfig: we could use a generic interface compatible both with helix and legacy
* HelixBasedCommModule: use finer grained comm module: we should decompose the coarse grained
* TaskSetup: isHelixEnabled : get through DI
* Cluster: ok, more general
* ClusterFromZk: correctly implement new methods from Cluster interface
* Main: some defaults to helix
* Server: could use helix optionally - code could belong to another class (Main?) - could
inject helix code ?
* remote senders / remote managers: there seems to be some ideas to refactor the current mechanism
into a state machine, but it's not implemented. We absolutely need this part since it is used
for injecting events (from an app adapter).
* UDP: not a priority, since we should first refactor to use netty there as well
> Enhance cluster management features in S4
> -----------------------------------------
>                 Key: S4-110
>                 URL:
>             Project: Apache S4
>          Issue Type: New Feature
>            Reporter: kishore gopalakrishna
>            Assignee: kishore gopalakrishna
>             Fix For: 0.6
> In S4 the number of partition is fixed for all streams and is dependent on the number
of nodes in the cluster.  Adding new nodes to S4 cluster causes the number of partitions to
change. This results in lot of data movement. For example if there are 4 nodes and you add
another node then nearly all keys will be remapped which result is huge data movement where
as ideally only 20% of the data should move.
> By using Helix, every stream can be  partitioned differently and independent of the number
of nodes. Helix distributes the partitions evenly among the nodes. When new nodes are added,
partitions can be migrated to new nodes without changing the number of partitions and  minimizes
the data movement.
> In S4 handles failures by having stand by nodes that are idle most of the time and become
active when a node fails. Even though this works, its not ideal in terms of efficient hardware
usage since the stand by nodes are idle most of the time. This also increases the fail over
time since the PE state has to be transfered to only one node. 
> Helix allows S4 to have Active and Standby nodes at a partition level so that all nodes
can be active but some partitions will be Active and some in stand by mode. When a node fails,
the partitions that were  Active on that node will be evenly distributed among the remaining
nodes. This provides automatic load balancing and also improves fail over time, since PE state
can be transfered to multiple nodes in parallel. 
> I have a prototype implementation here
> Instructions to build it and try it out are in the Readme.

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