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https://issues.apache.org/jira/browse/CALCITE-4515?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Julian Hyde resolved CALCITE-4515.
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Fix Version/s: 1.27.0
Resolution: Fixed
Fixed in
[93c30503|https://github.com/apache/calcite/commit/93c305031fb6c152c118390647f2b9b0979109c2];
thanks for the PR, [~vozerov]!
> 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: 1.26.0
> Reporter: Vladimir Ozerov
> Assignee: Vladimir Ozerov
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.27.0
>
> Time Spent: 10m
> Remaining Estimate: 0h
>
> {{JoinCommuteRule}} and {{JoinAssociateRule}} form a 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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