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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-909) Pitfall due to additional superstep after the iteration has stopped
Date Fri, 08 Aug 2014 08:27:12 GMT

    [ https://issues.apache.org/jira/browse/FLINK-909?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14090472#comment-14090472
] 

ASF GitHub Bot commented on FLINK-909:
--------------------------------------

Github user uce commented on the pull request:

    https://github.com/apache/incubator-flink/pull/91#issuecomment-51575648
  
    Nice addition to get rid of the empty last iteration. Looks good to me :-) I've posted
minor comments inline. After @rmetzger tested it, I think it's good to merge.
    
    Could you reproduce the memory issue (FLINK-945) locally? If yes, can you explain what
was the exact problem? I am wondering, because in theory the last iteration should not cause
any problems, right?



> Pitfall due to additional superstep after the iteration has stopped
> -------------------------------------------------------------------
>
>                 Key: FLINK-909
>                 URL: https://issues.apache.org/jira/browse/FLINK-909
>             Project: Flink
>          Issue Type: Bug
>            Reporter: GitHub Import
>            Assignee: Markus Holzemer
>              Labels: github-import
>             Fix For: pre-apache
>
>
> Currently, after an iteration has exceeded the maximum number of iterations, all tasks
are started again for an additional superstep during which they are stopped. This works if
a tasks only waits for dynamic input. However, in the case where one has a task, e.g. a coGroup
operation, which gets dynamic and static input the execution is not blocked. This can then
lead to erroneous behaviour which the user is not aware of.
> I had this problem implementing ALS. Here one has a loop which gets as dynamic input
matrix columns and as static input matrix entries. The columns and the entries are used to
construct a matrix which represents a system of linear equations. If the set of columns are
empty, then the matrix is singular and thus not solvable. During the additional superstep
the task won't receive any columns but would still try to solve the now singular matrix.
> It would be good to finish the iteration without initiating this additional superstep.
> ---------------- Imported from GitHub ----------------
> Url: https://github.com/stratosphere/stratosphere/issues/909
> Created by: [tillrohrmann|https://github.com/tillrohrmann]
> Labels: 
> Created at: Thu Jun 05 17:50:17 CEST 2014
> State: open



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