[jira] [Commented] (CALCITE-4514) Prefer merge new relset into old relset when they are parent set of each other

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

    [ https://issues.apache.org/jira/browse/CALCITE-4514?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17291489#comment-17291489 ] 

Vladimir Sitnikov commented on CALCITE-4514:
--------------------------------------------

I always assumed that the condition {{set.id > set2.id}} was there for the exact reason: compare old vs new set since ids are allocated sequentially. Does it work like that?

> Prefer merge new relset into old relset when they are parent set of each other
> ------------------------------------------------------------------------------
>
>                 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: 20m
>  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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