[jira] [Resolved] (CALCITE-3774) Add option to RelBuilder to prevent it from merging projects

["Julian Hyde (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CALCITE-3774?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Julian Hyde resolved CALCITE-3774.
----------------------------------
    Fix Version/s: 1.22.0
       Resolution: Fixed

Fixed in [555da953|https://github.com/apache/calcite/commit/555da953fe758a7d310aeb3aed463f3f2f3cdc3b].

The {{nodeCount}} is computed on creation in {{RexCall}} and {{RexWindow}}, computed in {{RexOver}} (a sub-class of {{RexCall}}), and 1 for most other sub-classes of {{RexNode}}.

> Add option to RelBuilder to prevent it from merging projects
> ------------------------------------------------------------
>
>                 Key: CALCITE-3774
>                 URL: https://issues.apache.org/jira/browse/CALCITE-3774
>             Project: Calcite
>          Issue Type: Bug
>    Affects Versions: 1.21.0
>            Reporter: Julian Hyde
>            Assignee: Julian Hyde
>            Priority: Major
>             Fix For: 1.22.0
>
>
> Add option to {{RelBuilder}} to prevent it from merging projects. Currently if you call {{RelBuilder.project}} and the input is a {{Project}} it will merge the expressions. This is usually a good idea, but sometimes it creates very complex expressions. In extreme cases Calcite can run out of memory.
> There is an existing method {{RelBuilder.shouldMergeProject()}} but by default it returns true, and in order to change it you have to sub-class {{RelBuilder}}, which is not easy to do.
> I propose to add a property {{RelBuilder.Config.mergeBloat}}, default 0, which would prevent creating a project that has more complexity than the two projects that went into it.
> Example 1:
>  * Input 1: {{Project(a+b+c+d AS w, b+c+d+e AS x, c+d+e+f AS y, d+e+f+g AS z)}} (complexity 28), followed by
>  * Input 2: {{Project(w*x AS p, x*y AS q, y*z AS r)}} (complexity 9) creates
>  * Output: {{Project((a+b+c+d) * (b+c+d+e) AS p, (b+c+d+e) * (c+d+e+f) AS q, (c+d+e+f) * (d+e+f+g) AS r)}}.
> The expression "a+b+c+d" has complexity 7 (4 fields and 3 calls). Input 1 has complexity 28 (4 expressions, each of complexity 7); input 2 has complexity 9 (3 expressions, each with complexity 3). Output has complexity 45 (3 expressions, each with complexity 15 (8 fields and 7 calls)). 45 is greater than 37 (28 + 9), so this merge would not be allowed.
> Example 2:
>  * Input 1: {{Project(a+b+c+d AS w, b+c+d+e AS x, c+d+e+f AS y, d+e+f+g AS z)}} (complexity 28), followed by
>  * Input 2: {{Project(w*x AS p, x*y AS q)}} (complexity 6) creates
>  * Output: {{Project((a+b+c+d) * (b+c+d+e) AS p, (b+c+d+e) * (c+d+e+f) AS q)}} (complexity 30).
> Output complexity 30 is less than input complexity 34 (28 + 6), and therefore the merge is allowed.



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