Pass collation to makeConst() instead of looking it up internally.

In nearly all cases, the caller already knows the correct collation, and
in a number of places, the value the caller has handy is more correct than
the default for the type would be.  (In particular, this patch makes it
significantly less likely that eval_const_expressions will result in
changing the exposed collation of an expression.)  So an internal lookup
is both expensive and wrong.

Author: tglsfdc

src/backend/commands/tablecmds.c

@@ -4337,10 +4337,12 @@ ATExecAddColumn(AlteredTableInfo *tab, Relation rel,
 		{
 			Oid			baseTypeId;
 			int32		baseTypeMod;
+			Oid			baseTypeColl;
 
 			baseTypeMod = typmod;
 			baseTypeId = getBaseTypeAndTypmod(typeOid, &baseTypeMod);
-			defval = (Expr *) makeNullConst(baseTypeId, baseTypeMod);
+			baseTypeColl = get_typcollation(baseTypeId);
+			defval = (Expr *) makeNullConst(baseTypeId, baseTypeMod, baseTypeColl);
 			defval = (Expr *) coerce_to_target_type(NULL,
 													(Node *) defval,
 													baseTypeId,

src/backend/executor/execQual.c

@@ -4653,7 +4653,7 @@ ExecInitExpr(Expr *node, PlanState *parent)
 						 * don't really care what type of NULL it is, so
 						 * always make an int4 NULL.
 						 */
-						e = (Expr *) makeNullConst(INT4OID, -1);
+						e = (Expr *) makeNullConst(INT4OID, -1, InvalidOid);
 					}
 					estate = ExecInitExpr(e, parent);
 					outlist = lappend(outlist, estate);

src/backend/executor/functions.c

@@ -1501,6 +1501,7 @@ check_sql_fn_retval(Oid func_id, Oid rettype, List *queryTreeList,
 					/* The type of the null we insert isn't important */
 					null_expr = (Expr *) makeConst(INT4OID,
 												   -1,
+												   InvalidOid,
 												   sizeof(int32),
 												   (Datum) 0,
 												   true,		/* isnull */
@@ -1562,6 +1563,7 @@ check_sql_fn_retval(Oid func_id, Oid rettype, List *queryTreeList,
 				/* The type of the null we insert isn't important */
 				null_expr = (Expr *) makeConst(INT4OID,
 											   -1,
+											   InvalidOid,
 											   sizeof(int32),
 											   (Datum) 0,
 											   true,	/* isnull */

src/backend/nodes/makefuncs.c

@@ -271,6 +271,7 @@ makeFromExpr(List *fromlist, Node *quals)
 Const *
 makeConst(Oid consttype,
 		  int32 consttypmod,
+		  Oid constcollid,
 		  int constlen,
 		  Datum constvalue,
 		  bool constisnull,
@@ -280,7 +281,7 @@ makeConst(Oid consttype,
 
 	cnst->consttype = consttype;
 	cnst->consttypmod = consttypmod;
-	cnst->constcollid = get_typcollation(consttype);
+	cnst->constcollid = constcollid;
 	cnst->constlen = constlen;
 	cnst->constvalue = constvalue;
 	cnst->constisnull = constisnull;
@@ -298,14 +299,15 @@ makeConst(Oid consttype,
  * storage properties.
  */
 Const *
-makeNullConst(Oid consttype, int32 consttypmod)
+makeNullConst(Oid consttype, int32 consttypmod, Oid constcollid)
 {
 	int16		typLen;
 	bool		typByVal;
 
 	get_typlenbyval(consttype, &typLen, &typByVal);
 	return makeConst(consttype,
 					 consttypmod,
+					 constcollid,
 					 (int) typLen,
 					 (Datum) 0,
 					 true,
@@ -320,7 +322,7 @@ Node *
 makeBoolConst(bool value, bool isnull)
 {
 	/* note that pg_type.h hardwires size of bool as 1 ... duplicate it */
-	return (Node *) makeConst(BOOLOID, -1, 1,
+	return (Node *) makeConst(BOOLOID, -1, InvalidOid, 1,
 							  BoolGetDatum(value), isnull, true);
 }
 

src/backend/optimizer/path/indxpath.c

@@ -19,6 +19,7 @@
 
 #include "access/skey.h"
 #include "catalog/pg_am.h"
+#include "catalog/pg_collation.h"
 #include "catalog/pg_operator.h"
 #include "catalog/pg_opfamily.h"
 #include "catalog/pg_type.h"
@@ -3233,7 +3234,9 @@ network_prefix_quals(Node *leftop, Oid expr_op, Oid opfamily, Datum rightop)
 
 	expr = make_opclause(opr1oid, BOOLOID, false,
 						 (Expr *) leftop,
-						 (Expr *) makeConst(datatype, -1, -1, opr1right,
+						 (Expr *) makeConst(datatype, -1,
+											InvalidOid,	/* not collatable */
+											-1, opr1right,
 											false, false),
 						 InvalidOid, InvalidOid);
 	result = list_make1(make_simple_restrictinfo(expr));
@@ -3249,7 +3252,9 @@ network_prefix_quals(Node *leftop, Oid expr_op, Oid opfamily, Datum rightop)
 
 	expr = make_opclause(opr2oid, BOOLOID, false,
 						 (Expr *) leftop,
-						 (Expr *) makeConst(datatype, -1, -1, opr2right,
+						 (Expr *) makeConst(datatype, -1,
+											InvalidOid,	/* not collatable */
+											-1, opr2right,
 											false, false),
 						 InvalidOid, InvalidOid);
 	result = lappend(result, make_simple_restrictinfo(expr));
@@ -3288,8 +3293,38 @@ static Const *
 string_to_const(const char *str, Oid datatype)
 {
 	Datum		conval = string_to_datum(str, datatype);
+	Oid			collation;
+	int			constlen;
 
-	return makeConst(datatype, -1,
-					 ((datatype == NAMEOID) ? NAMEDATALEN : -1),
+	/*
+	 * We only need to support a few datatypes here, so hard-wire properties
+	 * instead of incurring the expense of catalog lookups.
+	 */
+	switch (datatype)
+	{
+		case TEXTOID:
+		case VARCHAROID:
+		case BPCHAROID:
+			collation = DEFAULT_COLLATION_OID;
+			constlen = -1;
+			break;
+
+		case NAMEOID:
+			collation = InvalidOid;
+			constlen = NAMEDATALEN;
+			break;
+
+		case BYTEAOID:
+			collation = InvalidOid;
+			constlen = -1;
+			break;
+
+		default:
+			elog(ERROR, "unexpected datatype in string_to_const: %u",
+				 datatype);
+			return NULL;
+	}
+
+	return makeConst(datatype, -1, collation, constlen,
 					 conval, false, false);
 }

src/backend/optimizer/plan/planagg.c

@@ -429,7 +429,8 @@ build_minmax_path(PlannerInfo *root, MinMaxAggInfo *mminfo,
 
 	/* set up expressions for LIMIT 1 */
 	parse->limitOffset = NULL;
-	parse->limitCount = (Node *) makeConst(INT8OID, -1, sizeof(int64),
+	parse->limitCount = (Node *) makeConst(INT8OID, -1, InvalidOid,
+										   sizeof(int64),
 										   Int64GetDatum(1), false,
 										   FLOAT8PASSBYVAL);
 

src/backend/optimizer/prep/preptlist.c

@@ -269,6 +269,7 @@ expand_targetlist(List *tlist, int command_type,
 					{
 						new_expr = (Node *) makeConst(atttype,
 													  -1,
+													  attcollation,
 													  att_tup->attlen,
 													  (Datum) 0,
 													  true,		/* isnull */
@@ -286,6 +287,7 @@ expand_targetlist(List *tlist, int command_type,
 						/* Insert NULL for dropped column */
 						new_expr = (Node *) makeConst(INT4OID,
 													  -1,
+													  InvalidOid,
 													  sizeof(int32),
 													  (Datum) 0,
 													  true,		/* isnull */
@@ -307,6 +309,7 @@ expand_targetlist(List *tlist, int command_type,
 						/* Insert NULL for dropped column */
 						new_expr = (Node *) makeConst(INT4OID,
 													  -1,
+													  InvalidOid,
 													  sizeof(int32),
 													  (Datum) 0,
 													  true,		/* isnull */

src/backend/optimizer/prep/prepunion.c

@@ -910,6 +910,7 @@ generate_setop_tlist(List *colTypes, int flag,
 		/* flag value is the given constant */
 		expr = (Node *) makeConst(INT4OID,
 								  -1,
+								  InvalidOid,
 								  sizeof(int4),
 								  Int32GetDatum(flag),
 								  false,