1 files changed, 50 insertions, 23 deletions

diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index dd748acffdf..c1d860ceffd 100644
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -2520,7 +2520,43 @@ deparse_context_for(const char *aliasname, Oid relid)
 }
 
 /*
- * deparse_context_for_planstate	- Build deparse context for a plan
+ * deparse_context_for_plan_rtable - Build deparse context for a plan's rtable
+ *
+ * When deparsing an expression in a Plan tree, we use the plan's rangetable
+ * to resolve names of simple Vars.  The initialization of column names for
+ * this is rather expensive if the rangetable is large, and it'll be the same
+ * for every expression in the Plan tree; so we do it just once and re-use
+ * the result of this function for each expression.  (Note that the result
+ * is not usable until set_deparse_context_planstate() is applied to it.)
+ *
+ * In addition to the plan's rangetable list, pass the per-RTE alias names
+ * assigned by a previous call to select_rtable_names_for_explain.
+ */
+List *
+deparse_context_for_plan_rtable(List *rtable, List *rtable_names)
+{
+	deparse_namespace *dpns;
+
+	dpns = (deparse_namespace *) palloc0(sizeof(deparse_namespace));
+
+	/* Initialize fields that stay the same across the whole plan tree */
+	dpns->rtable = rtable;
+	dpns->rtable_names = rtable_names;
+	dpns->ctes = NIL;
+
+	/*
+	 * Set up column name aliases.  We will get rather bogus results for join
+	 * RTEs, but that doesn't matter because plan trees don't contain any join
+	 * alias Vars.
+	 */
+	set_simple_column_names(dpns);
+
+	/* Return a one-deep namespace stack */
+	return list_make1(dpns);
+}
+
+/*
+ * set_deparse_context_planstate	- Specify Plan node containing expression
  *
  * When deparsing an expression in a Plan tree, we might have to resolve
  * OUTER_VAR, INNER_VAR, or INDEX_VAR references.  To do this, the caller must
@@ -2533,43 +2569,34 @@ deparse_context_for(const char *aliasname, Oid relid)
  * fields, which won't contain INDEX_VAR Vars.)
  *
  * Note: planstate really ought to be declared as "PlanState *", but we use
- * "Node *" to avoid having to include execnodes.h in builtins.h.
+ * "Node *" to avoid having to include execnodes.h in ruleutils.h.
  *
  * The ancestors list is a list of the PlanState's parent PlanStates, the
  * most-closely-nested first.  This is needed to resolve PARAM_EXEC Params.
  * Note we assume that all the PlanStates share the same rtable.
  *
- * The plan's rangetable list must also be passed, along with the per-RTE
- * alias names assigned by a previous call to select_rtable_names_for_explain.
- * (We use the rangetable to resolve simple Vars, but the plan inputs are
- * necessary for Vars with special varnos.)
+ * Once this function has been called, deparse_expression() can be called on
+ * subsidiary expression(s) of the specified PlanState node.  To deparse
+ * expressions of a different Plan node in the same Plan tree, re-call this
+ * function to identify the new parent Plan node.
+ *
+ * The result is the same List passed in; this is a notational convenience.
  */
 List *
-deparse_context_for_planstate(Node *planstate, List *ancestors,
-							  List *rtable, List *rtable_names)
+set_deparse_context_planstate(List *dpcontext,
+							  Node *planstate, List *ancestors)
 {
 	deparse_namespace *dpns;
 
-	dpns = (deparse_namespace *) palloc0(sizeof(deparse_namespace));
-
-	/* Initialize fields that stay the same across the whole plan tree */
-	dpns->rtable = rtable;
-	dpns->rtable_names = rtable_names;
-	dpns->ctes = NIL;
-
-	/*
-	 * Set up column name aliases.  We will get rather bogus results for join
-	 * RTEs, but that doesn't matter because plan trees don't contain any join
-	 * alias Vars.
-	 */
-	set_simple_column_names(dpns);
+	/* Should always have one-entry namespace list for Plan deparsing */
+	Assert(list_length(dpcontext) == 1);
+	dpns = (deparse_namespace *) linitial(dpcontext);
 
 	/* Set our attention on the specific plan node passed in */
 	set_deparse_planstate(dpns, (PlanState *) planstate);
 	dpns->ancestors = ancestors;
 
-	/* Return a one-deep namespace stack */
-	return list_make1(dpns);
+	return dpcontext;
 }
 
 /*