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https://issues.apache.org/jira/browse/FLINK-951?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14053543#comment-14053543
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Markus Holzemer commented on FLINK-951:
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With this change it now makes a difference if you specify
getIterationRuntimeContext().addIterationAccumulator() or
getIterationRuntimeContext().addAccumulator().
With the addIterationAccumulator() the registered accumulator will be reset
after each iterations, same like aggregators before. When you do the old
addAccumulator() inside of iterations it will have the same functionality as
before, which means it will not be reset.
> Reworking of Iteration Synchronization, Accumulators and Aggregators
> --------------------------------------------------------------------
>
> Key: FLINK-951
> URL: https://issues.apache.org/jira/browse/FLINK-951
> Project: Flink
> Issue Type: Improvement
> Components: Optimizer
> Affects Versions: 0.6-incubating
> Reporter: Markus Holzemer
> Assignee: Markus Holzemer
> Labels: refactoring
> Original Estimate: 168h
> Remaining Estimate: 168h
>
> I just realized that there is no real Jira issue for the task I am currently
> working on.
> I am currently reworking a few things regarding Iteration Synchronization,
> Accumulators and Aggregators. Currently the synchronization at the end of one
> superstep is done through channel events. That makes it hard to track the
> current status of iterations. That is why I am changing this synchronization
> to use RPC calls with the JobManager, so that the JobManager manages the
> current status of all iterations.
> Currently we use Accumulators outside of iterations and Aggregators inside of
> iterations. Both have a similiar function, but a bit different interfaces and
> handling. I want to unify these two concepts. I propose that we stick in the
> future to Accumulators only. Aggregators therefore are removed and
> Accumulators are extended to cover the usecases Aggregators were used fore
> before. The switch to RPC for iterations makes it possible to also send the
> current Accumulator values at the end of each superstep, so that the
> JobManager (and thereby the webinterface) will be able to print intermediate
> accumulation results.
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