Add SupportRequestInlineInFrom planner support request.HEADorigin/masterorigin/HEADmaster

This request allows a support function to replace a function call
appearing in FROM (typically a set-returning function) with an
equivalent SELECT subquery.  The subquery will then be subject
to the planner's usual optimizations, potentially allowing a much
better plan to be generated.  While the planner has long done this
automatically for simple SQL-language functions, it's now possible
for extensions to do it for functions outside that group.
Notably, this could be useful for functions that are presently
implemented in PL/pgSQL and work by generating and then EXECUTE'ing
a 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

1 files changed, 30 insertions, 0 deletions

diff --git a/src/include/nodes/supportnodes.h b/src/include/nodes/supportnodes.h
index 7b623d54058..ea774c7ef6a 100644
--- a/src/include/nodes/supportnodes.h
+++ b/src/include/nodes/supportnodes.h
@@ -39,6 +39,8 @@ typedef struct PlannerInfo PlannerInfo; /* avoid including pathnodes.h here */
 typedef struct IndexOptInfo IndexOptInfo;
 typedef struct SpecialJoinInfo SpecialJoinInfo;
 typedef struct WindowClause WindowClause;
+typedef struct RangeTblFunction RangeTblFunction;	/* ditto for parsenodes.h */
+typedef struct HeapTupleData *HeapTuple;	/* and htup.h too */
 
 /*
  * The Simplify request allows the support function to perform plan-time
@@ -70,6 +72,34 @@ typedef struct SupportRequestSimplify
 } SupportRequestSimplify;
 
 /*
+ * The InlineInFrom request allows the support function to perform plan-time
+ * simplification of a call to its target function that appears in FROM.
+ * The rules for this are sufficiently different from ordinary expressions
+ * that it's best to make this a separate request from Simplify.
+ *
+ * The planner's PlannerInfo "root" is typically not needed, but can be
+ * consulted if it's necessary to obtain info about Vars present in
+ * the given node tree.  Beware that root could be NULL in some usages.
+ *
+ * "rtfunc" will be a RangeTblFunction node for the support function's target
+ * function.  The call appeared alone (and without ORDINALITY) in FROM.
+ *
+ * "proc" will be the HeapTuple for the pg_proc row of the target function.
+ *
+ * The result should be a semantically-equivalent SELECT Query tree,
+ * or NULL if no simplification could be performed.  The tree must have
+ * been passed through parse analysis and rewrite.
+ */
+typedef struct SupportRequestInlineInFrom
+{
+	NodeTag		type;
+
+	PlannerInfo *root;			/* Planner's infrastructure */
+	RangeTblFunction *rtfunc;	/* Function call to be simplified */
+	HeapTuple	proc;			/* Function definition from pg_proc */
+} SupportRequestInlineInFrom;
+
+/*
  * The Selectivity request allows the support function to provide a
  * selectivity estimate for a function appearing at top level of a WHERE
  * clause (so it applies only to functions returning boolean).