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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-3257) Add Exactly-Once Processing Guarantees in Iterative DataStream Jobs
Date Mon, 12 Dec 2016 11:05:58 GMT

    [ https://issues.apache.org/jira/browse/FLINK-3257?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15741633#comment-15741633

ASF GitHub Bot commented on FLINK-3257:

Github user senorcarbone commented on the issue:

    Hey again, @StephanEwen @uce .
    When you have 10 min can you take a look to see if this is acceptable?  
    I would not like to leave this here for months again, it has been out way too long already.

    The changes are just a few and straightforward so I really encourage you to skim them
at your earliest convenience. Thanks!

> Add Exactly-Once Processing Guarantees in Iterative DataStream Jobs
> -------------------------------------------------------------------
>                 Key: FLINK-3257
>                 URL: https://issues.apache.org/jira/browse/FLINK-3257
>             Project: Flink
>          Issue Type: Improvement
>            Reporter: Paris Carbone
>            Assignee: Paris Carbone
> The current snapshotting algorithm cannot support cycles in the execution graph. An alternative
scheme can potentially include records in-transit through the back-edges of a cyclic execution
graph (ABS [1]) to achieve the same guarantees.
> One straightforward implementation of ABS for cyclic graphs can work as follows along
the lines:
> 1) Upon triggering a barrier in an IterationHead from the TaskManager start block output
and start upstream backup of all records forwarded from the respective IterationSink.
> 2) The IterationSink should eventually forward the current snapshotting epoch barrier
to the IterationSource.
> 3) Upon receiving a barrier from the IterationSink, the IterationSource should finalize
the snapshot, unblock its output and emit all records in-transit in FIFO order and continue
the usual execution.
> --
> Upon restart the IterationSource should emit all records from the injected snapshot first
and then continue its usual execution.
> Several optimisations and slight variations can be potentially achieved but this can
be the initial implementation take.
> [1] http://arxiv.org/abs/1506.08603

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