[jira] [Commented] (CALCITE-5715) Prune old nodes after projection merging in ProjectMergeRule

["Ruben Q L (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CALCITE-5715?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17738289#comment-17738289 ] 

Ruben Q L commented on CALCITE-5715:
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[~libenchao] what's the status on this one? Given the proximity of 1.35 RC, shall we remove the "fixVersion=1.35" from here?

> Prune old nodes after projection merging in ProjectMergeRule
> ------------------------------------------------------------
>
>                 Key: CALCITE-5715
>                 URL: https://issues.apache.org/jira/browse/CALCITE-5715
>             Project: Calcite
>          Issue Type: Improvement
>          Components: core
>    Affects Versions: 1.34.0
>            Reporter: Benchao Li
>            Priority: Major
>             Fix For: 1.35.0
>
>
> We already have many similar usages (prune old nodes when the new one is obviously better, e.g. in [CalcMergeRule|https://github.com/apache/calcite/blob/c56d5564628de6b3265f960764a6f6fc43935a75/core/src/main/java/org/apache/calcite/rel/rules/CalcMergeRule.java#L85-L90] to reduce the search scope, I propose to also add this for {{ProjectMergeRule}}. Do you have any concerns about this?
> In {{ProjectMergeRule}}, there is a case that after merging the two {{Project}}, we'll find the new Project is trivial and we'll transform to the bottomProject's input(https://github.com/apache/calcite/blob/c56d5564628de6b3265f960764a6f6fc43935a75/core/src/main/java/org/apache/calcite/rel/rules/ProjectMergeRule.java#L132-L139). In this case, both topProject and bottomProject could be pruned?
> The reason I propose to do this optimization for {{ProjectMergeRule}} is that I met a problem that two sets will point to each other after projection merging, and the planner will run into dead loop. (It's hard to show the details, I haven't got a simple reproducible demo yet)



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