[jira] [Resolved] (CALCITE-4302) Improve cost propagation in volcano to avoid re-propagation

["Danny Chen (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CALCITE-4302?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Danny Chen resolved CALCITE-4302.
---------------------------------
    Fix Version/s: 1.27.0
         Assignee: Danny Chen
       Resolution: Fixed

Fixed in [c7fdae2|https://github.com/apache/calcite/commit/c7fdae22fb0e6b220152f05a7343ce5569283a83], thanks for your PR, [~botong] ~

> Improve cost propagation in volcano to avoid re-propagation
> -----------------------------------------------------------
>
>                 Key: CALCITE-4302
>                 URL: https://issues.apache.org/jira/browse/CALCITE-4302
>             Project: Calcite
>          Issue Type: Improvement
>            Reporter: Botong Huang
>            Assignee: Danny Chen
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 1.27.0
>
>          Time Spent: 5h 40m
>  Remaining Estimate: 0h
>
> CALCITE-3330 changed the cost propagation in volcano from DFS to BFS. However, there is still room for improvement. A subset can be updated more than once in a cost propagation process. For instance, A -> D, A -> B -> C -> D. When subset A has an update, using BFS subset D (and thus all subsets above/after D) can be updated twice, first via A -> D and then C -> D. We can further improve the BFS by always popping the relNode with the smallest cost from the queue, similar to the Dijkstra algorithm. So that whenever a relNode is popped from the queue, its current best cannot be further deceased any more. As a result, all subsets will only be propagated at most once. 



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