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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 12:36:14 GMT

    [ https://issues.apache.org/jira/browse/FLINK-909?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14090714#comment-14090714
] 

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

Github user StephanEwen commented on a diff in the pull request:

    https://github.com/apache/incubator-flink/pull/91#discussion_r15990179
  
    --- Diff: flink-runtime/src/main/java/org/apache/flink/runtime/iterative/task/AbstractIterativePactTask.java
---
    @@ -210,28 +210,17 @@ public RuntimeAggregatorRegistry getIterationAggregators() {
     		return this.iterationAggregators;
     	}
     
    -	protected void checkForTerminationAndResetEndOfSuperstepState() throws IOException {
    +	protected void verifyEndOfSuperstepState() throws IOException {
    --- End diff --
    
    The is still a sanity check, but the distinction between end-of-superstep and termination
comes no longer from the readers, but from the specific shared sync.


> 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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