Elide not-null constraint checks on child tables during PK creation

We were unnecessarily acquiring AccessExclusiveLock on all child tables
when "ALTER TABLE ONLY sometab ADD PRIMARY KEY" was run on their parent
table, an oversight in commit 14e87ffa5c.  This caused deadlocks
during pg_restore of partitioned tables.

The reason to acquire the AEL was that we need to verify that child
tables have the involved columns already marked as not-null; but if the
parent table has an inheritable not-null constraint, then all children
must necessarily be in the correct state already, so we can skip the
check, which avoids acquiring the lock.  Reorder the code so that it
works that way.  This doesn't change things in the case where the
constraint doesn't exist, but that case is of lesser importance because
it doesn't occur during parallel pg_restore.

While at it, reword some errmsg() and add errhint() to similar cases in
related but not adjacent code.

Diagnosed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Tender Wang <tndrwang@gmail.com>
Discussion: https://postgr.es/m/67469c1c-38bc-7d94-918a-67033f5dd731@gmx.net
Discussion: https://postgr.es/m/2045026.1743801143@sss.pgh.pa.us
Discussion: https://postgr.es/m/1280408.1744650810@sss.pgh.pa.us

src/test/regress/expected/constraints.out

@@ -1042,6 +1042,7 @@ ALTER TABLE ATACC2 INHERIT ATACC1;
 -- can't override
 ALTER TABLE ATACC1 ADD CONSTRAINT ditto NOT NULL a;
 ERROR:  cannot change NO INHERIT status of NOT NULL constraint "a_is_not_null" on relation "atacc2"
+HINT:  You might need to make the existing constraint inheritable using ALTER TABLE ... ALTER CONSTRAINT ... INHERIT.
 -- dropping the NO INHERIT constraint allows this to work
 ALTER TABLE ATACC2 DROP CONSTRAINT a_is_not_null;
 ALTER TABLE ATACC1 ADD CONSTRAINT ditto NOT NULL a;
@@ -1233,8 +1234,8 @@ Indexes:
 create table cnn_pk (a int not null no inherit);
 alter table cnn_pk add primary key (a);
 ERROR:  cannot create primary key on column "a"
-DETAIL:  The constraint "cnn_pk_a_not_null" on column "a", marked NO INHERIT, is incompatible with a primary key.
-HINT:  You will need to make it inheritable using ALTER TABLE ... ALTER CONSTRAINT ... INHERIT.
+DETAIL:  The constraint "cnn_pk_a_not_null" on column "a" of table "cnn_pk", marked NO INHERIT, is incompatible with a primary key.
+HINT:  You might need to make the existing constraint inheritable using ALTER TABLE ... ALTER CONSTRAINT ... INHERIT.
 drop table cnn_pk;
 -- Ensure partitions are scanned for null values when adding a PK
 create table cnn2_parted(a int) partition by list (a);
@@ -1389,14 +1390,15 @@ Not-null constraints:
 -- If we have an invalid constraint, we can't have another
 ALTER TABLE notnull_tbl1 ADD CONSTRAINT nn1 NOT NULL a NOT VALID NO INHERIT;
 ERROR:  cannot change NO INHERIT status of NOT NULL constraint "nn" on relation "notnull_tbl1"
+HINT:  You might need to make the existing constraint inheritable using ALTER TABLE ... ALTER CONSTRAINT ... INHERIT.
 ALTER TABLE notnull_tbl1 ADD CONSTRAINT nn NOT NULL a;
 ERROR:  incompatible NOT VALID constraint "nn" on relation "notnull_tbl1"
-HINT:  You will need to use ALTER TABLE ... VALIDATE CONSTRAINT to validate it.
+HINT:  You might need to validate it using ALTER TABLE ... VALIDATE CONSTRAINT.
 -- cannot add primary key on a column with an invalid not-null
 ALTER TABLE notnull_tbl1 ADD PRIMARY KEY (a);
 ERROR:  cannot create primary key on column "a"
-DETAIL:  The constraint "nn" on column "a", marked NOT VALID, is incompatible with a primary key.
-HINT:  You will need to validate it using ALTER TABLE ... VALIDATE CONSTRAINT.
+DETAIL:  The constraint "nn" on column "a" of table "notnull_tbl1", marked NOT VALID, is incompatible with a primary key.
+HINT:  You might need to validate it using ALTER TABLE ... VALIDATE CONSTRAINT.
 -- ALTER column SET NOT NULL validates an invalid constraint (but this fails
 -- because of rows with null values)
 ALTER TABLE notnull_tbl1 ALTER a SET NOT NULL;
@@ -1502,7 +1504,7 @@ NOTICE:  merging multiple inherited definitions of column "i"
 ALTER TABLE notnull_inhparent ADD CONSTRAINT nn NOT NULL i NOT VALID;
 ALTER TABLE notnull_inhchild ADD CONSTRAINT nn1 NOT NULL i; -- error
 ERROR:  incompatible NOT VALID constraint "nn" on relation "notnull_inhchild"
-HINT:  You will need to use ALTER TABLE ... VALIDATE CONSTRAINT to validate it.
+HINT:  You might need to validate it using ALTER TABLE ... VALIDATE CONSTRAINT.
 EXECUTE get_nnconstraint_info('{notnull_inhparent, notnull_inhchild, notnull_inhgrand}');
       tabname      | conname | convalidated | conislocal | coninhcount 
 -------------------+---------+--------------+------------+-------------
@@ -1567,6 +1569,24 @@ ERROR:  constraint "nn1" conflicts with NOT VALID constraint on child table "pp_
 ALTER TABLE pp_nn_1 VALIDATE CONSTRAINT nn1;
 ALTER TABLE pp_nn ATTACH PARTITION pp_nn_1 FOR VALUES IN (NULL,5); --ok
 DROP TABLE pp_nn;
+-- Try a partition with an invalid constraint and create a PK on the parent.
+CREATE TABLE pp_nn (a int) PARTITION BY HASH (a);
+CREATE TABLE pp_nn_1 PARTITION OF pp_nn FOR VALUES WITH (MODULUS 2, REMAINDER 0);
+ALTER TABLE pp_nn_1 ADD CONSTRAINT nn NOT NULL a NOT VALID;
+ALTER TABLE ONLY pp_nn ADD PRIMARY KEY (a);
+ERROR:  cannot create primary key on column "a"
+DETAIL:  The constraint "nn" on column "a" of table "pp_nn_1", marked NOT VALID, is incompatible with a primary key.
+HINT:  You might need to validate it using ALTER TABLE ... VALIDATE CONSTRAINT.
+DROP TABLE pp_nn;
+-- same as above, but the constraint is NO INHERIT
+CREATE TABLE pp_nn (a int) PARTITION BY HASH (a);
+CREATE TABLE pp_nn_1 PARTITION OF pp_nn FOR VALUES WITH (MODULUS 2, REMAINDER 0);
+ALTER TABLE pp_nn_1 ADD CONSTRAINT nn NOT NULL a NO INHERIT;
+ALTER TABLE ONLY pp_nn ADD PRIMARY KEY (a);
+ERROR:  cannot create primary key on column "a"
+DETAIL:  The constraint "nn" on column "a" of table "pp_nn_1", marked NO INHERIT, is incompatible with a primary key.
+HINT:  You might need to make the existing constraint inheritable using ALTER TABLE ... ALTER CONSTRAINT ... INHERIT.
+DROP TABLE pp_nn;
 -- Create table with NOT NULL INVALID constraint, for pg_upgrade.
 CREATE TABLE notnull_tbl1_upg (a int, b int);
 INSERT INTO notnull_tbl1_upg VALUES (NULL, 1), (NULL, 2), (300, 3);

src/test/regress/expected/inherit.out

@@ -2286,6 +2286,7 @@ DETAIL:  The column has an inherited not-null constraint.
 -- change NO INHERIT status of inherited constraint: no dice, it's inherited
 alter table cc2 add not null a2 no inherit;
 ERROR:  cannot change NO INHERIT status of NOT NULL constraint "nn" on relation "cc2"
+HINT:  You might need to make the existing constraint inheritable using ALTER TABLE ... ALTER CONSTRAINT ... INHERIT.
 -- remove constraint from cc2: no dice, it's inherited
 alter table cc2 alter column a2 drop not null;
 ERROR:  cannot drop inherited constraint "nn" of relation "cc2"
@@ -2509,6 +2510,7 @@ CREATE TABLE inh_nn_parent (a int, NOT NULL a NO INHERIT);
 CREATE TABLE inh_nn_child() INHERITS (inh_nn_parent);
 ALTER TABLE inh_nn_parent ADD CONSTRAINT nna NOT NULL a;
 ERROR:  cannot change NO INHERIT status of NOT NULL constraint "inh_nn_parent_a_not_null" on relation "inh_nn_parent"
+HINT:  You might need to make the existing constraint inheritable using ALTER TABLE ... ALTER CONSTRAINT ... INHERIT.
 ALTER TABLE inh_nn_parent ALTER a SET NOT NULL;
 ERROR:  cannot change NO INHERIT status of NOT NULL constraint "inh_nn_parent_a_not_null" on relation "inh_nn_parent"
 DROP TABLE inh_nn_parent cascade;
@@ -2520,6 +2522,7 @@ CREATE TABLE inh_nn_lvl2 () INHERITS (inh_nn_lvl1);
 CREATE TABLE inh_nn_lvl3 (CONSTRAINT foo NOT NULL a NO INHERIT) INHERITS (inh_nn_lvl2);
 ALTER TABLE inh_nn_lvl1 ADD PRIMARY KEY (a);
 ERROR:  cannot change NO INHERIT status of NOT NULL constraint "foo" on relation "inh_nn_lvl3"
+HINT:  You might need to make the existing constraint inheritable using ALTER TABLE ... ALTER CONSTRAINT ... INHERIT.
 DROP TABLE inh_nn_lvl1, inh_nn_lvl2, inh_nn_lvl3;
 -- Disallow specifying conflicting NO INHERIT flags for the same constraint
 CREATE TABLE inh_nn1 (a int primary key, b int, not null a no inherit);

src/test/regress/sql/constraints.sql

@@ -940,6 +940,20 @@ ALTER TABLE pp_nn_1 VALIDATE CONSTRAINT nn1;
 ALTER TABLE pp_nn ATTACH PARTITION pp_nn_1 FOR VALUES IN (NULL,5); --ok
 DROP TABLE pp_nn;
 
+-- Try a partition with an invalid constraint and create a PK on the parent.
+CREATE TABLE pp_nn (a int) PARTITION BY HASH (a);
+CREATE TABLE pp_nn_1 PARTITION OF pp_nn FOR VALUES WITH (MODULUS 2, REMAINDER 0);
+ALTER TABLE pp_nn_1 ADD CONSTRAINT nn NOT NULL a NOT VALID;
+ALTER TABLE ONLY pp_nn ADD PRIMARY KEY (a);
+DROP TABLE pp_nn;
+
+-- same as above, but the constraint is NO INHERIT
+CREATE TABLE pp_nn (a int) PARTITION BY HASH (a);
+CREATE TABLE pp_nn_1 PARTITION OF pp_nn FOR VALUES WITH (MODULUS 2, REMAINDER 0);
+ALTER TABLE pp_nn_1 ADD CONSTRAINT nn NOT NULL a NO INHERIT;
+ALTER TABLE ONLY pp_nn ADD PRIMARY KEY (a);
+DROP TABLE pp_nn;
+
 -- Create table with NOT NULL INVALID constraint, for pg_upgrade.
 CREATE TABLE notnull_tbl1_upg (a int, b int);
 INSERT INTO notnull_tbl1_upg VALUES (NULL, 1), (NULL, 2), (300, 3);