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From "Aimee Cheng (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (S4-110) Enhance cluster management features in S4
Date Tue, 29 Jan 2013 10:47:26 GMT

    [ https://issues.apache.org/jira/browse/S4-110?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13565272#comment-13565272
] 

Aimee Cheng commented on S4-110:
--------------------------------

Hi Kishore,

Sorry for replying late. I am not sure about what's your understanding about the current distribute
mechanism of S4. From my side, I think it will provide a workflow when user write the app
class, for example, creating a stream, and set this stream to some PEs. So when we do these,
just as what I said above, different PEs can receive different streams, so if every stream
have different partition, the logic seems have some problems.

I also want to know your understanding on that. Thanks.

                
> Enhance cluster management features in S4
> -----------------------------------------
>
>                 Key: S4-110
>                 URL: https://issues.apache.org/jira/browse/S4-110
>             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 https://github.com/kishoreg/incubator-s4
> Instructions to build it and try it out are in the Readme.

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