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Commitb140c8d

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Add SupportRequestInlineInFrom planner support request.
This request allows a support function to replace a function callappearing in FROM (typically a set-returning function) with anequivalent SELECT subquery. The subquery will then be subjectto the planner's usual optimizations, potentially allowing a muchbetter plan to be generated. While the planner has long done thisautomatically for simple SQL-language functions, it's now possiblefor extensions to do it for functions outside that group.Notably, this could be useful for functions that are presentlyimplemented in PL/pgSQL and work by generating and then EXECUTE'inga SQL query.Author: Paul A Jungwirth <pj@illuminatedcomputing.com>Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>Discussion:https://postgr.es/m/09de6afa-c33d-4d94-a5cb-afc6cea0d2bb@illuminatedcomputing.com
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‎doc/src/sgml/xfunc.sgml‎

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@@ -4159,6 +4159,31 @@ supportfn(internal) returns internal
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expression and an actual execution of the target function.
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</para>
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<para>
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<literal>SupportRequestSimplify</literal> is not used
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for <link linkend="queries-tablefunctions">set-returning
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functions</link>. Instead, support functions can implement
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the <literal>SupportRequestInlineInFrom</literal> request to expand
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function calls appearing in the <literal>FROM</literal> clause of a
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query. (It's also allowed to support this request for
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non-set-returning functions, although
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typically <literal>SupportRequestSimplify</literal> would serve as
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well.) For this request type, a successful result must be
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a <literal>SELECT</literal> Query tree, which will replace
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the <literal>FROM</literal> item as though a sub-select had been
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written instead. The Query tree must appear as it would after parse
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analysis and rewrite processing. One way to ensure that that's true
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is to build a SQL string then feed it
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through <function>pg_parse_query</function>
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and <function>pg_analyze_and_rewrite</function>, or related
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functions. <literal>PARAM_EXTERN</literal> <structname>Param</structname>
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nodes can appear within the Query to represent the function's
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arguments; they will be replaced by the actual argument expressions.
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As with <literal>SupportRequestSimplify</literal>, it is the support
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function's responsibility that the replacement Query be equivalent to
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normal execution of the target function.
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</para>
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<para>
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For target functions that return <type>boolean</type>, it is often useful to estimate
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the fraction of rows that will be selected by a <literal>WHERE</literal> clause using that

‎src/backend/optimizer/prep/prepjointree.c‎

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@@ -1066,13 +1066,15 @@ pull_up_sublinks_qual_recurse(PlannerInfo *root, Node *node,
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/*
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* preprocess_function_rtes
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*Constant-simplify any FUNCTION RTEs in the FROM clause, and then
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*attempt to "inline" any thatare set-returning functions.
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*attempt to "inline" any thatcan be converted to simple subqueries.
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*
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* If an RTE_FUNCTION rtable entry invokes a set-returning function that
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* If an RTE_FUNCTION rtable entry invokes a set-returningSQLfunction that
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* contains just a simple SELECT, we can convert the rtable entry to an
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* RTE_SUBQUERY entry exposing the SELECT directly. This is especially
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* useful if the subquery can then be "pulled up" for further optimization,
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* but we do it even if not, to reduce executor overhead.
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* RTE_SUBQUERY entry exposing the SELECT directly. Other sorts of functions
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* are also inline-able if they have a support function that can generate
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* the replacement sub-Query. This is especially useful if the subquery can
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* then be "pulled up" for further optimization, but we do it even if not,
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* to reduce executor overhead.
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*
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* This has to be done before we have started to do any optimization of
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* subqueries, else any such steps wouldn't get applied to subqueries
@@ -1107,7 +1109,7 @@ preprocess_function_rtes(PlannerInfo *root)
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eval_const_expressions(root, (Node*)rte->functions);
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/* Check safety of expansion, and expand if possible */
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funcquery=inline_set_returning_function(root,rte);
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funcquery=inline_function_in_from(root,rte);
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if (funcquery)
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{
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/* Successful expansion, convert the RTE to a subquery */

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