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https://issues.apache.org/jira/browse/CALCITE-4514?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17292247#comment-17292247
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Vladimir Sitnikov commented on CALCITE-4514:
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{quote} It is at least better than compute from scratch every time it is
needed. I am not sure if there is a better way.{quote}
Is it really needed to compute the set?
If the set is not needed, we do not need to add it to the cache either.
{quote} Performance side, this Jira is originally intended to fix and improve
performance{quote}
We had recently seen a case when a small change resulted in a noticeable
performance regression.
Of course, caching the {{Set<...>}} looks like to be "always faster", however,
it might result in an unintentional memory leak.
> Fine tune the merge order of two RelSets, cache RelSet's childSet computation
> -----------------------------------------------------------------------------
>
> Key: CALCITE-4514
> URL: https://issues.apache.org/jira/browse/CALCITE-4514
> Project: Calcite
> Issue Type: Improvement
> Reporter: Botong Huang
> Priority: Minor
> Labels: pull-request-available
> Time Spent: 0.5h
> Remaining Estimate: 0h
>
> When merging two relsets, we have two preferences:
> 1. Merge parent relset into child relset
> 2. Merge newer relset into older relset
> Currently, when the two relsets are parent set of each other, we randomly
> pick a merge order without checking the second condition above. For
> performance reasons, we should, to avoid unnecessary churn.
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