When using extended-query protocol, postpone planning of unnamed statements

until Bind is received, so that actual parameter values are visible to the
planner.  Make use of the parameter values for estimation purposes (but
don't fold them into the actual plan).  This buys back most of the
potential loss of plan quality that ensues from using out-of-line
parameters instead of putting literal values right into the query text.

This patch creates a notion of constant-folding expressions 'for
estimation purposes only', in which case we can be more aggressive than
the normal eval_const_expressions() logic can be.  Right now the only
difference in behavior is inserting bound values for Params, but it will
be interesting to look at other possibilities.  One that we've seen
come up repeatedly is reducing now() and related functions to current
values, so that queries like ... WHERE timestampcol > now() - '1 day'
have some chance of being planned effectively.

Oliver Jowett, with some kibitzing from Tom Lane.

1 files changed, 41 insertions, 16 deletions

diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 07b60969a45..976b417e096 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/tcop/postgres.c,v 1.419 2004/06/06 00:41:27 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/tcop/postgres.c,v 1.420 2004/06/11 01:09:00 tgl Exp $
  *
  * NOTES
  *	  this is the "main" module of the postgres backend and
@@ -630,7 +630,7 @@ pg_rewrite_queries(List *querytree_list)
 
 /* Generate a plan for a single already-rewritten query. */
 Plan *
-pg_plan_query(Query *querytree)
+pg_plan_query(Query *querytree, ParamListInfo boundParams)
 {
 	Plan	   *plan;
 
@@ -642,7 +642,7 @@ pg_plan_query(Query *querytree)
 		ResetUsage();
 
 	/* call the optimizer */
-	plan = planner(querytree, false, 0);
+	plan = planner(querytree, false, 0, boundParams);
 
 	if (log_planner_stats)
 		ShowUsage("PLANNER STATISTICS");
@@ -687,7 +687,8 @@ pg_plan_query(Query *querytree)
  * statements in the rewriter's output.)
  */
 List *
-pg_plan_queries(List *querytrees, bool needSnapshot)
+pg_plan_queries(List *querytrees, ParamListInfo boundParams,
+				bool needSnapshot)
 {
 	List	   *plan_list = NIL;
 	ListCell   *query_list;
@@ -709,7 +710,7 @@ pg_plan_queries(List *querytrees, bool needSnapshot)
 				SetQuerySnapshot();
 				needSnapshot = false;
 			}
-			plan = pg_plan_query(query);
+			plan = pg_plan_query(query, boundParams);
 		}
 
 		plan_list = lappend(plan_list, plan);
@@ -867,7 +868,7 @@ exec_simple_query(const char *query_string)
 
 		querytree_list = pg_analyze_and_rewrite(parsetree, NULL, 0);
 
-		plantree_list = pg_plan_queries(querytree_list, true);
+		plantree_list = pg_plan_queries(querytree_list, NULL, true);
 
 		/* If we got a cancel signal in analysis or planning, quit */
 		CHECK_FOR_INTERRUPTS();
@@ -1205,7 +1206,14 @@ exec_parse_message(const char *query_string,	/* string to execute */
 
 		querytree_list = pg_rewrite_queries(querytree_list);
 
-		plantree_list = pg_plan_queries(querytree_list, true);
+		/*
+		 * If this is the unnamed statement and it has parameters, defer
+		 * query planning until Bind.  Otherwise do it now.
+		 */
+		if (!is_named && numParams > 0)
+			plantree_list = NIL;
+		else
+			plantree_list = pg_plan_queries(querytree_list, NULL, true);
 	}
 	else
 	{
@@ -1291,6 +1299,7 @@ exec_bind_message(StringInfo input_message)
 	PreparedStatement *pstmt;
 	Portal		portal;
 	ParamListInfo params;
+	bool		isaborted = IsAbortedTransactionBlockState();
 
 	pgstat_report_activity("<BIND>");
 
@@ -1356,13 +1365,6 @@ exec_bind_message(StringInfo input_message)
 	else
 		portal = CreatePortal(portal_name, false, false);
 
-	PortalDefineQuery(portal,
-					  pstmt->query_string,
-					  pstmt->commandTag,
-					  pstmt->query_list,
-					  pstmt->plan_list,
-					  pstmt->context);
-
 	/*
 	 * Fetch parameters, if any, and store in the portal's memory context.
 	 *
@@ -1372,7 +1374,6 @@ exec_bind_message(StringInfo input_message)
 	 */
 	if (numParams > 0)
 	{
-		bool		isaborted = IsAbortedTransactionBlockState();
 		ListCell   *l;
 		MemoryContext oldContext;
 
@@ -1516,8 +1517,32 @@ exec_bind_message(StringInfo input_message)
 	pq_getmsgend(input_message);
 
 	/*
-	 * Start portal execution.
+	 * If we didn't plan the query before, do it now.  This allows the
+	 * planner to make use of the concrete parameter values we now have.
+	 *
+	 * This happens only for unnamed statements, and so switching into
+	 * the statement context for planning is correct (see notes in
+	 * exec_parse_message).
 	 */
+	if (pstmt->plan_list == NIL && pstmt->query_list != NIL &&
+		!isaborted)
+	{
+		MemoryContext oldContext = MemoryContextSwitchTo(pstmt->context);
+
+		pstmt->plan_list = pg_plan_queries(pstmt->query_list, params, true);
+		MemoryContextSwitchTo(oldContext);
+	}
+
+	/*
+	 * Define portal and start execution.
+	 */
+	PortalDefineQuery(portal,
+					  pstmt->query_string,
+					  pstmt->commandTag,
+					  pstmt->query_list,
+					  pstmt->plan_list,
+					  pstmt->context);
+
 	PortalStart(portal, params);
 
 	/*