[jira] [Updated] (CALCITE-4515) Do not generate the new join tree from commute/associate rules if there are "always true" conditions

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

     [ https://issues.apache.org/jira/browse/CALCITE-4515?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Vladimir Ozerov updated CALCITE-4515:
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    Summary: Do not generate the new join tree from commute/associate rules if there are "always true" conditions  (was: Do not generate the new join tree from commute/associate rules if it contains "always true" condition)

> Do not generate the new join tree from commute/associate rules if there are "always true" conditions
> ----------------------------------------------------------------------------------------------------
>
>                 Key: CALCITE-4515
>                 URL: https://issues.apache.org/jira/browse/CALCITE-4515
>             Project: Calcite
>          Issue Type: Improvement
>          Components: core
>    Affects Versions: 1.27.0
>            Reporter: Vladimir Ozerov
>            Assignee: Vladimir Ozerov
>            Priority: Major
>
> {{JoinCommuteRule}} and {{JoinAssociateRule}} are the complete ruleset to generate all bushy trees (plus join-project transposes to counter new projects created during commute).
> These rules do not check whether the new join trees contain an always {{TRUE}} condition which is a cross-product. Such join trees are not optimal in the majority of cases, and practical optimizers might want to suppress them.
> In this ticket, I propose to add a configuration property to {{JoinCommuteRule}} and {{JoinAssociateRule}} to disable the creation of trees with always {{TRUE}} condition:
>  # The property should be disabled by default because sometimes cross-products might be present in the query on purpose (e.g., see [https://dl.acm.org/doi/10.5555/645916.671976], page 315)
>  # We consider the "always {{TRUE}}" condition only, even though they represent only part of cross-products. The reason is that it might be difficult and expensive to understand whether the condition is cross-join or not (e.g., for hypergraphs). On the other hand, the check for "always true" is cheap and robust. We assume that the user might need to do some pre-processing (e.g., filter push-down) to take advantage of the new property. 
> # We do not extend the {{JoinPushThroughJoinRule}} for now, since the [commute + associate] ruleset already explores all bushy trees and testing of the new property for {{JoinPushThroughJoinRule}} is difficult. We may extend this rule in a separate ticket if needed.
>  



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