Support creation of FK in NOT VALID state for partitioned tables.

If the PG server version is at least 18, the foreign key in NOT VALID state
can be created. (If the partitioned table is on the PK side, the FK constraint
in NOT VALID state can be created even in earlier PG versions.)

Author: Antonin Houska

README.md

@@ -166,14 +166,16 @@ table. It's recommended to handle constraints creation this way:
 
 5.  FOREIGN KEY constraints are also created automatically (according to the
     source table) and need to be validated using the `ALTER TABLE ... VALIDATE
-    CONSTRAINT ...` command, unless the referencing table is partitioned: the
-    NOT VALID option is currently not supported for partitioned tables.
-
-    Therefore, if the referencing table is partitioned, you need to use the
-    `ALTER TABLE ... ADD CONSTRAINT ... FOREIGN KEY ...` command after
-    `rewrite_table()` has finished. Please run the command as soon as possible
-    to minimize the risk that applications modify the database in a way that
-    violates the constraints.
+    CONSTRAINT ...` command, unless the referencing table is partitioned and
+    the version of PostgreSQL server is 17 or lower: those versions do not
+    support the NOT VALID option for partitioned tables.
+
+    Therefore, if the referencing table is partitioned and if the server
+    version is 17 or lower, you need to use the `ALTER TABLE ... ADD
+    CONSTRAINT ... FOREIGN KEY ...` command after `rewrite_table()` has
+    finished. Please run the command as soon as possible to minimize the risk
+    that applications modify the database in a way that violates the
+    constraints.
 
 6.  Drop all foreign keys involving the source table.
 

expected/pg_rewrite.out

@@ -227,7 +227,7 @@ TABLE tab4;
 
 -- One more test for "manual" validation of FKs, this time we rewrite the PK
 -- table. The NOT VALID constraint cannot be used if the FK table is
--- partitioned, so we need a separate test.
+-- partitioned and if PG version is < 18, so we need a separate test.
 CREATE TABLE tab1_pk(i int primary key);
 INSERT INTO tab1_pk(i) VALUES (1);
 CREATE TABLE tab1_pk_new(i bigint primary key);

pg_rewrite.c

@@ -3260,9 +3260,10 @@ dump_fk_constraint(HeapTuple tup, Oid relid_dst, const char *relname_dst,
 
 	if (con->conrelid == relid_src)
 	{
+#if PG_VERSION_NUM < 180000
 		/*
-		 * ALTER TABLE ... ADD CONSTRAINT ... FOREIGN KEY ... NOT VALID is
-		 * currently not supported for partitioned FK table.
+		 * ALTER TABLE ... ADD CONSTRAINT ... FOREIGN KEY ... NOT VALID is not
+		 * supported for partitioned FK table in PG < 18.
 		 */
 		if (get_rel_relkind(relid_dst) == RELKIND_PARTITIONED_TABLE)
 		{
@@ -3272,6 +3273,7 @@ dump_fk_constraint(HeapTuple tup, Oid relid_dst, const char *relname_dst,
 						 NULL);
 			return;
 		}
+#endif
 
 		fknsp = get_namespace_name(relid_dst);
 		fkrelname = relname_dst;

sql/pg_rewrite.sql

@@ -92,7 +92,7 @@ TABLE tab4;
 
 -- One more test for "manual" validation of FKs, this time we rewrite the PK
 -- table. The NOT VALID constraint cannot be used if the FK table is
--- partitioned, so we need a separate test.
+-- partitioned and if PG version is < 18, so we need a separate test.
 CREATE TABLE tab1_pk(i int primary key);
 INSERT INTO tab1_pk(i) VALUES (1);
 CREATE TABLE tab1_pk_new(i bigint primary key);