Enable CHECK constraints to be declared NOT VALID

This means that they can initially be added to a large existing table
without checking its initial contents, but new tuples must comply to
them; a separate pass invoked by ALTER TABLE / VALIDATE can verify
existing data and ensure it complies with the constraint, at which point
it is marked validated and becomes a normal part of the table ecosystem.

An non-validated CHECK constraint is ignored in the planner for
constraint_exclusion purposes; when validated, cached plans are
recomputed so that partitioning starts working right away.

This patch also enables domains to have unvalidated CHECK constraints
attached to them as well by way of ALTER DOMAIN / ADD CONSTRAINT / NOT
VALID, which can later be validated with ALTER DOMAIN / VALIDATE
CONSTRAINT.

Thanks to Thom Brown, Dean Rasheed and Jaime Casanova for the various
reviews, and Robert Hass for documentation wording improvement
suggestions.

This patch was sponsored by Enova Financial.

src/test/regress/sql/alter_table.sql

@@ -236,12 +236,41 @@ DELETE FROM tmp3 where a=5;
 ALTER TABLE tmp3 validate constraint tmpconstr;
 ALTER TABLE tmp3 validate constraint tmpconstr;
 
+-- Try a non-verified CHECK constraint
+ALTER TABLE tmp3 ADD CONSTRAINT b_greater_than_ten CHECK (b > 10); -- fail
+ALTER TABLE tmp3 ADD CONSTRAINT b_greater_than_ten CHECK (b > 10) NOT VALID; -- succeeds
+ALTER TABLE tmp3 VALIDATE CONSTRAINT b_greater_than_ten; -- fails
+DELETE FROM tmp3 WHERE NOT b > 10;
+ALTER TABLE tmp3 VALIDATE CONSTRAINT b_greater_than_ten; -- succeeds
+ALTER TABLE tmp3 VALIDATE CONSTRAINT b_greater_than_ten; -- succeeds
+
+-- Test inherited NOT VALID CHECK constraints
+select * from tmp3;
+CREATE TABLE tmp6 () INHERITS (tmp3);
+CREATE TABLE tmp7 () INHERITS (tmp3);
+
+INSERT INTO tmp6 VALUES (6, 30), (7, 16);
+ALTER TABLE tmp3 ADD CONSTRAINT b_le_20 CHECK (b <= 20) NOT VALID;
+ALTER TABLE tmp3 VALIDATE CONSTRAINT b_le_20;	-- fails
+DELETE FROM tmp6 WHERE b > 20;
+ALTER TABLE tmp3 VALIDATE CONSTRAINT b_le_20;	-- succeeds
+
+-- An already validated constraint must not be revalidated
+CREATE FUNCTION boo(int) RETURNS int IMMUTABLE STRICT LANGUAGE plpgsql AS $$ BEGIN RAISE NOTICE 'boo: %', $1; RETURN $1; END; $$;
+INSERT INTO tmp7 VALUES (8, 18);
+ALTER TABLE tmp7 ADD CONSTRAINT identity CHECK (b = boo(b));
+ALTER TABLE tmp3 ADD CONSTRAINT IDENTITY check (b = boo(b)) NOT VALID;
+ALTER TABLE tmp3 VALIDATE CONSTRAINT identity;
 
 -- Try (and fail) to create constraint from tmp5(a) to tmp4(a) - unique constraint on
 -- tmp4 is a,b
 
 ALTER TABLE tmp5 add constraint tmpconstr foreign key(a) references tmp4(a) match full;
 
+DROP TABLE tmp7;
+
+DROP TABLE tmp6;
+
 DROP TABLE tmp5;
 
 DROP TABLE tmp4;
@@ -250,6 +279,23 @@ DROP TABLE tmp3;
 
 DROP TABLE tmp2;
 
+-- NOT VALID with plan invalidation -- ensure we don't use a constraint for
+-- exclusion until validated
+set constraint_exclusion TO 'partition';
+create table nv_parent (d date); 
+create table nv_child_2010 () inherits (nv_parent);
+create table nv_child_2011 () inherits (nv_parent);
+alter table nv_child_2010 add check (d between '2010-01-01'::date and '2010-12-31'::date) not valid;
+alter table nv_child_2011 add check (d between '2011-01-01'::date and '2011-12-31'::date) not valid;
+explain (costs off) select * from nv_parent where d between '2011-08-01' and '2011-08-31';
+create table nv_child_2009 (check (d between '2009-01-01'::date and '2009-12-31'::date)) inherits (nv_parent);
+explain (costs off) select * from nv_parent where d between '2011-08-01'::date and '2011-08-31'::date;
+explain (costs off) select * from nv_parent where d between '2009-08-01'::date and '2009-08-31'::date;
+-- after validation, the constraint should be used
+alter table nv_child_2011 VALIDATE CONSTRAINT nv_child_2011_d_check;
+explain (costs off) select * from nv_parent where d between '2009-08-01'::date and '2009-08-31'::date;
+
+
 -- Foreign key adding test with mixed types
 
 -- Note: these tables are TEMP to avoid name conflicts when this test