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https://issues.apache.org/jira/browse/FLINK-33940?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17800416#comment-17800416
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Gyula Fora commented on FLINK-33940:
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If we are going to change this, powers of 2 are not really good as they only
allow you to double the parallelism.
it’s better to consider factorial or highly composite numbers
([https://mathworld.wolfram.com/HighlyCompositeNumber.html)] for practical use.
> Update the auto-derivation rule of max parallelism for enlarged upscaling
> space
> -------------------------------------------------------------------------------
>
> Key: FLINK-33940
> URL: https://issues.apache.org/jira/browse/FLINK-33940
> Project: Flink
> Issue Type: Improvement
> Components: API / Core
> Reporter: Zhanghao Chen
> Priority: Major
>
> *Background*
> The choice of the max parallelism of an stateful operator is important as it
> limits the upper bound of the parallelism of the opeartor while it can also
> add extra overhead when being set too large. Currently, the max parallelism
> of an opeartor is either fixed to a value specified by API core / pipeline
> option or auto-derived with the following rules:
> {{min(max(roundUpToPowerOfTwo(operatorParallelism * 1.5), 128), 32767)}}
> *Problem*
> Recently, the elasticity of Flink jobs is becoming more and more valued by
> users. The current auto-derived max parallelism was introduced a time time
> ago and only allows the operator parallelism to be roughly doubled, which is
> not desired for elasticity. Setting an max parallelism manually may not be
> desired as well: users may not have the sufficient expertise to select a good
> max-parallelism value.
> *Proposal*
> Update the auto-derivation rule of max parallelism to derive larger max
> parallelism for better elasticity experience out of the box. A candidate is
> as follows:
> {{min(max(roundUpToPowerOfTwo(operatorParallelism * {*}5{*}), {*}1024{*}),
> 32767)}}
> Looking forward to your opinions on this.
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