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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 08:21:12 GMT

    [ https://issues.apache.org/jira/browse/FLINK-909?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14090465#comment-14090465

ASF GitHub Bot commented on FLINK-909:

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

    --- Diff: flink-runtime/src/main/java/org/apache/flink/runtime/iterative/concurrent/SuperstepKickoffLatchBroker.java
    @@ -0,0 +1,32 @@
    + * Licensed to the Apache Software Foundation (ASF) under one
    + * or more contributor license agreements.  See the NOTICE file
    + * distributed with this work for additional information
    + * regarding copyright ownership.  The ASF licenses this file
    + * to you under the Apache License, Version 2.0 (the
    + * "License"); you may not use this file except in compliance
    + * with the License.  You may obtain a copy of the License at
    + *
    + *     http://www.apache.org/licenses/LICENSE-2.0
    + *
    + * Unless required by applicable law or agreed to in writing, software
    + * distributed under the License is distributed on an "AS IS" BASIS,
    + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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    + */
    --- End diff --
    blank line

> 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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