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https://issues.apache.org/jira/browse/TEZ-3126?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15154796#comment-15154796
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Jonathan Eagles commented on TEZ-3126:
--------------------------------------
My bad. I took a look at the math behind the current algorithm and it is
completely correct based on the assumption that all task outputs are equal in
size. How do you feel about switching this jira to logging the reason for not
reducing parallelism.
\\cc [~rohini].
> Auto-Reduce Parallelism: Vertex not re-configured when reduced by less than
> half.
> ---------------------------------------------------------------------------------
>
> Key: TEZ-3126
> URL: https://issues.apache.org/jira/browse/TEZ-3126
> Project: Apache Tez
> Issue Type: Bug
> Reporter: Jonathan Eagles
> Assignee: Jonathan Eagles
> Priority: Critical
> Attachments: TEZ-3126.1.patch
>
>
> For example, when reducing parallelism from 36 to 22. The basePartitionRange
> will be 1 and will not re-configure the vertex.
> {code:java|title=ShuffleVertexManager#determineParallelismAndApply|borderStyle=dashed|bgColor=lightgrey}
> int desiredTaskParallelism =
> (int)(
> (expectedTotalSourceTasksOutputSize+desiredTaskInputDataSize-1)/
> desiredTaskInputDataSize);
> if(desiredTaskParallelism < minTaskParallelism) {
> desiredTaskParallelism = minTaskParallelism;
> }
>
> if(desiredTaskParallelism >= currentParallelism) {
> return true;
> }
>
> // most shufflers will be assigned this range
> basePartitionRange = currentParallelism/desiredTaskParallelism;
>
> if (basePartitionRange <= 1) {
> // nothing to do if range is equal 1 partition. shuffler does it by
> default
> return true;
> }
> {code}
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