[jira] [Closed] (CALCITE-4501) Clear costs in VolcanoPlanner when setting the new root

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

     [ https://issues.apache.org/jira/browse/CALCITE-4501?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Vladimir Ozerov closed CALCITE-4501.
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> Clear costs in VolcanoPlanner when setting the new root
> -------------------------------------------------------
>
>                 Key: CALCITE-4501
>                 URL: https://issues.apache.org/jira/browse/CALCITE-4501
>             Project: Calcite
>          Issue Type: Improvement
>          Components: core
>    Affects Versions: 1.26.0
>            Reporter: Vladimir Ozerov
>            Assignee: Vladimir Ozerov
>            Priority: Minor
>          Time Spent: 20m
>  Remaining Estimate: 0h
>
> In production-grade systems, the optimization is typically performed in several phases. The same instance of {{VolcanoPlanner}} tends to be re-used between the phases. 
> In some sophisticated scenarios, we may want to alter the cost function between phases. 
> For example, to adjust the weights of some operators depending on some heuristics, or even switch to a completely different cost model. 
> One way to do that is to re-instantiate the cluster and the planner with the new cost function. 
> However, it requires copying of the current rel tree, because its nodes still point to the old cluster. This may negatively affect the performance. 
> The alternative approach could be to change the state of the cost factory. However, it would not work for two reasons:
> # The cluster object has a reference to {{MetadataQuery}} with possibly cached costs. This may lead to a mix of different cost models.
> # {{VolcanoPlanner}} caches zero and infinite costs in a final variable.
> In this issue, I propose to introduce two slight modifications to the {{VolcanoPlanner}}:
> # Clear the metadata query from within {{setRoot}} method.
> # Make {{infCost}} and {{zeroCost}} non-final, and also re-initialize them in the {{setRoot}} method.
> The {{setRoot}} method is convenient for these purposes because it is invoked from the {{RuleSetProgram}}, so the desired cost cleanup will work with no modifications to the application's code.
> Please let me know if you think that this change is not valid.



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