Allow ON UPDATE/DELETE SET DEFAULT plans to be cached.

Once upon a time, somebody was worried that cached RI plans wouldn't get
remade with new default values after ALTER TABLE ... SET DEFAULT, so they
didn't allow caching of plans for ON UPDATE/DELETE SET DEFAULT actions.
That time is long gone, though (and even at the time I doubt this was the
greatest hazard posed by ALTER TABLE...).  So allow these triggers to cache
their plans just like the others.

The cache_plan argument to ri_PlanCheck is now vestigial, since there
are no callers that don't pass "true"; but I left it alone in case there
is any future need for it.

src/backend/utils/adt/ri_triggers.c

@@ -2155,12 +2155,12 @@ RI_FKey_setdefault_del(PG_FUNCTION_ARGS)
 				elog(ERROR, "SPI_connect failed");
 
 			/*
-			 * Prepare a plan for the set default delete operation.
-			 * Unfortunately we need to do it on every invocation because the
-			 * default value could potentially change between calls.
+			 * Fetch or prepare a saved plan for the set default delete
+			 * operation
 			 */
 			ri_BuildQueryKey(&qkey, &riinfo, RI_PLAN_SETDEFAULT_DEL_DOUPDATE);
 
+			if ((qplan = ri_FetchPreparedPlan(&qkey)) == NULL)
 			{
 				StringInfoData querybuf;
 				StringInfoData qualbuf;
@@ -2207,9 +2207,9 @@ RI_FKey_setdefault_del(PG_FUNCTION_ARGS)
 				}
 				appendStringInfoString(&querybuf, qualbuf.data);
 
-				/* Prepare the plan, don't save it */
+				/* Prepare and save the plan */
 				qplan = ri_PlanCheck(querybuf.data, riinfo.nkeys, queryoids,
-									 &qkey, fk_rel, pk_rel, false);
+									 &qkey, fk_rel, pk_rel, true);
 			}
 
 			/*
@@ -2239,7 +2239,7 @@ RI_FKey_setdefault_del(PG_FUNCTION_ARGS)
 			return PointerGetDatum(NULL);
 
 			/*
-			 * Handle MATCH PARTIAL set null delete.
+			 * Handle MATCH PARTIAL set default delete.
 			 */
 		case FKCONSTR_MATCH_PARTIAL:
 			ereport(ERROR,
@@ -2348,12 +2348,12 @@ RI_FKey_setdefault_upd(PG_FUNCTION_ARGS)
 				elog(ERROR, "SPI_connect failed");
 
 			/*
-			 * Prepare a plan for the set default delete operation.
-			 * Unfortunately we need to do it on every invocation because the
-			 * default value could potentially change between calls.
+			 * Fetch or prepare a saved plan for the set default update
+			 * operation
 			 */
 			ri_BuildQueryKey(&qkey, &riinfo, RI_PLAN_SETDEFAULT_UPD_DOUPDATE);
 
+			if ((qplan = ri_FetchPreparedPlan(&qkey)) == NULL)
 			{
 				StringInfoData querybuf;
 				StringInfoData qualbuf;
@@ -2400,9 +2400,9 @@ RI_FKey_setdefault_upd(PG_FUNCTION_ARGS)
 				}
 				appendStringInfoString(&querybuf, qualbuf.data);
 
-				/* Prepare the plan, don't save it */
+				/* Prepare and save the plan */
 				qplan = ri_PlanCheck(querybuf.data, riinfo.nkeys, queryoids,
-									 &qkey, fk_rel, pk_rel, false);
+									 &qkey, fk_rel, pk_rel, true);
 			}
 
 			/*
@@ -2432,7 +2432,7 @@ RI_FKey_setdefault_upd(PG_FUNCTION_ARGS)
 			return PointerGetDatum(NULL);
 
 			/*
-			 * Handle MATCH PARTIAL set null delete.
+			 * Handle MATCH PARTIAL set default update.
 			 */
 		case FKCONSTR_MATCH_PARTIAL:
 			ereport(ERROR,

src/test/regress/expected/foreign_key.out

@@ -1319,3 +1319,39 @@ begin;
 (2 rows)
 
 commit;
+--
+-- Test that SET DEFAULT actions recognize updates to default values
+--
+create temp table defp (f1 int primary key);
+NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "defp_pkey" for table "defp"
+create temp table defc (f1 int default 0
+                        references defp on delete set default);
+insert into defp values (0), (1), (2);
+insert into defc values (2);
+select * from defc;
+ f1 
+----
+  2
+(1 row)
+
+delete from defp where f1 = 2;
+select * from defc;
+ f1 
+----
+  0
+(1 row)
+
+delete from defp where f1 = 0; -- fail
+ERROR:  update or delete on table "defp" violates foreign key constraint "defc_f1_fkey" on table "defc"
+DETAIL:  Key (f1)=(0) is still referenced from table "defc".
+alter table defc alter column f1 set default 1;
+delete from defp where f1 = 0;
+select * from defc;
+ f1 
+----
+  1
+(1 row)
+
+delete from defp where f1 = 1; -- fail
+ERROR:  update or delete on table "defp" violates foreign key constraint "defc_f1_fkey" on table "defc"
+DETAIL:  Key (f1)=(1) is still referenced from table "defc".

src/test/regress/sql/foreign_key.sql

@@ -943,3 +943,20 @@ begin;
     update selfref set a = 456 where a = 123;
     select a, b from selfref;
 commit;
+
+--
+-- Test that SET DEFAULT actions recognize updates to default values
+--
+create temp table defp (f1 int primary key);
+create temp table defc (f1 int default 0
+                        references defp on delete set default);
+insert into defp values (0), (1), (2);
+insert into defc values (2);
+select * from defc;
+delete from defp where f1 = 2;
+select * from defc;
+delete from defp where f1 = 0; -- fail
+alter table defc alter column f1 set default 1;
+delete from defp where f1 = 0;
+select * from defc;
+delete from defp where f1 = 1; -- fail