[jira] [Commented] (CALCITE-4514) Fine tune the merge order of two RelSets, cache RelSet's childSet computation

["Vladimir Sitnikov (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CALCITE-4514?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17292039#comment-17292039 ] 

Vladimir Sitnikov commented on CALCITE-4514:
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Are we using https://en.wikipedia.org/wiki/Disjoint-set_data_structure#Merging_two_sets here?
Then {{set2.getChildSets(this).contains(set)}} looks strange.
Do we really need it there?

> 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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