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https://issues.apache.org/jira/browse/FLINK-3888?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15543133#comment-15543133
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Vasia Kalavri commented on FLINK-3888:
--------------------------------------
I had a quick look into this and I don't see any fundamental reason why we
can't add a custom convergence criterion in delta iterations. It seems that it
is currently allowed to add one convergence criterion only, and since delta
iterations have the {{WorksetEmptyConvergenceCriterion}} by default, adding a
custom one is not possible.
So, one solution could be the following:
1. use {{TaskConfig.setConvergenceCriterion()}} to set the custom, user-defined
convergence criterion (like in the case of bulk iteration)
2. add a new method {{TaskConfig.setDefaultConvergeCriterion()}} to add the
default empty workset convergence
3. check both criteria in
{{IterationSynchronizationSinkTask.checkForConvergence()}}
4. expose the custom convergence criterion in {{DeltaIteration}}
If I'm not missing something and this seems acceptable I'd like to resolve this
issue. Custom convergence would be helpful in several Gelly algorithms.
> Custom Aggregator with Convergence can't be registered directly with
> DeltaIteration
> -----------------------------------------------------------------------------------
>
> Key: FLINK-3888
> URL: https://issues.apache.org/jira/browse/FLINK-3888
> Project: Flink
> Issue Type: Bug
> Components: Iterations
> Reporter: Martin Liesenberg
>
> Contrary to the
> [documentation|https://ci.apache.org/projects/flink/flink-docs-master/apis/batch/iterations.html]
> the method to add an aggregator with a custom convergence criterion to a
> DeltaIteration is not exposed directly to DeltaIteration, but can only be
> accessed via the {{aggregatorRegistry}}.
> Moreover, when registering an aggregator with a custom convergence criterion
> and running the program, the following exception appears in the logs:
> {noformat}
> Error: Cannot use custom convergence criterion with workset iteration.
> Workset iterations have implicit convergence criterion where workset is empty.
> org.apache.flink.optimizer.CompilerException: Error: Cannot use custom
> convergence criterion with workset iteration. Workset iterations have
> implicit convergence criterion where workset is empty.
> at
> org.apache.flink.optimizer.plantranslate.JobGraphGenerator.finalizeWorksetIteration(JobGraphGenerator.java:1518)
> at
> org.apache.flink.optimizer.plantranslate.JobGraphGenerator.compileJobGraph(JobGraphGenerator.java:198)
> at
> org.apache.flink.optimizer.plantranslate.JobGraphGenerator.compileJobGraph(JobGraphGenerator.java:164)
> at
> org.apache.flink.test.util.TestEnvironment.execute(TestEnvironment.java:76)
> at
> org.apache.flink.api.java.ExecutionEnvironment.execute(ExecutionEnvironment.java:898)
> at org.apache.flink.api.java.DataSet.collect(DataSet.java:410)
> at org.apache.flink.api.java.DataSet.print(DataSet.java:1605)
> {noformat}
> The issue has been found while discussing FLINK-2926
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