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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-8532) RebalancePartitioner should use Random value for its first partition
Date Tue, 21 Aug 2018 16:09:00 GMT

    [ https://issues.apache.org/jira/browse/FLINK-8532?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16587661#comment-16587661
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ASF GitHub Bot commented on FLINK-8532:
---------------------------------------

Guibo-Pan commented on issue #6544: [FLINK-8532] [Streaming] modify RebalancePartitioner to
use a random partition as its first partition
URL: https://github.com/apache/flink/pull/6544#issuecomment-414729790
 
 
   Hi @tillrohrmann , does this PR look good to you, and could you help advance it? thanks.

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> RebalancePartitioner should use Random value for its first partition
> --------------------------------------------------------------------
>
>                 Key: FLINK-8532
>                 URL: https://issues.apache.org/jira/browse/FLINK-8532
>             Project: Flink
>          Issue Type: Improvement
>          Components: DataStream API
>            Reporter: Yuta Morisawa
>            Assignee: Guibo Pan
>            Priority: Major
>              Labels: pull-request-available
>
> In some conditions, RebalancePartitioner doesn't balance data correctly because it
use the same value for selecting next operators.
> RebalancePartitioner initializes its partition id using the same value in every threads,
so it indeed balances data, but at one moment the amount of data in each operator is skew.
> Particularly, when the data rate of  former operators is equal , data skew becomes severe.
>  
>  
> Example:
> Consider a simple operator chain.
> -> map1 -> rebalance -> map2 ->
> Each map operator(map1, map2) contains three subtasks(subtask 1, 2, 3, 4, 5, 6).
> map1          map2
>  st1              st4
>  st2              st5
>  st3              st6
>  
> At the beginning, every subtasks in map1 sends data to st4 in map2 because they use the
same initial parition id.
> Next time the map1 receive data st1,2,3 send data to st5 because they increment its partition
id when they processed former data.
> In my environment,  it takes twice the time to process data when I use RebalancePartitioner 
as long as I use other partitioners(rescale, keyby).
>  
> To solve this problem, in my opinion, RebalancePartitioner should use its own operator
id for the initial value.
>  



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