Test additional speculative conflict scenarios.

Previously, the speculative insert tests did not cover the case when a
tuple t is inserted into a table with a unique index on a column but
before it can insert into the index, a concurrent transaction has
inserted a conflicting value into the index and the insertion of tuple t
must be aborted.

The basic permutation is one session successfully inserts into the table
and an associated unique index while a concurrent session successfully
inserts into the table but discovers a conflict before inserting into
the index and must abort the insertion.

Several variants on this include:
- swap which session is successful
- first session insert transaction does not commit, so second session
must wait on a transaction lock
- first session insert does not "complete", so second session must wait
on a speculative insertion lock

Also, refactor the existing TOAST table upsert test to be in the same
spec and reuse the steps.

Author: Melanie Plageman, Ashwin Agrawal, Andres Freund
Reviewed-by: Andres Freund, Taylor Vesely
Discussion: https://postgr.es/m/CAAKRu_ZRmxy_OEryfY3G8Zp01ouhgw59_-_Cm8n7LzRH5BAvng@mail.gmail.com

src/test/isolation/expected/insert-conflict-toast.out

-Parsed test spec with 3 sessions
-
-starting permutation: s2insert s3insert s1commit
-pg_advisory_xact_lock
-
-               
-step s2insert: 
-  INSERT INTO ctoast (key, val) VALUES (1, ctoast_large_val()) ON CONFLICT DO NOTHING;
- <waiting ...>
-step s3insert: 
-  INSERT INTO ctoast (key, val) VALUES (1, ctoast_large_val()) ON CONFLICT DO NOTHING;
- <waiting ...>
-step s1commit: COMMIT;
-step s2insert: <... completed>
-step s3insert: <... completed>

src/test/isolation/isolation_schedule

@@ -38,7 +38,6 @@ test: insert-conflict-do-nothing-2
 test: insert-conflict-do-update
 test: insert-conflict-do-update-2
 test: insert-conflict-do-update-3
-test: insert-conflict-toast
 test: insert-conflict-specconflict
 test: delete-abort-savept
 test: delete-abort-savept-2

src/test/isolation/specs/insert-conflict-toast.spec

-# INSERT...ON CONFLICT test on table with TOAST
-#
-# This test verifies that speculatively inserted toast rows do not
-# cause conflicts. It does so by using expression index over a
-# function which acquires an advisory lock, triggering two index
-# insertions to happen almost at the same time. This is not guaranteed
-# to lead to a failed speculative insertion, but makes one quite
-# likely.
-
-setup
-{
-  CREATE TABLE ctoast (key int primary key, val text);
-  CREATE OR REPLACE FUNCTION ctoast_lock_func(int) RETURNS INT IMMUTABLE LANGUAGE SQL AS 'select pg_advisory_xact_lock_shared(1); select $1;';
-  CREATE OR REPLACE FUNCTION ctoast_large_val() RETURNS TEXT LANGUAGE SQL AS 'select array_agg(md5(g::text))::text from generate_series(1, 256) g';
-  CREATE UNIQUE INDEX ctoast_lock_idx ON ctoast (ctoast_lock_func(key));
-}
-
-teardown
-{
-  DROP TABLE ctoast;
-  DROP FUNCTION ctoast_lock_func(int);
-  DROP FUNCTION ctoast_large_val();
-}
-
-session "s1"
-setup
-{
-  BEGIN ISOLATION LEVEL READ COMMITTED;
-  SELECT pg_advisory_xact_lock(1);
-}
-step "s1commit" { COMMIT; }
-
-session "s2"
-setup
-{
-  SET default_transaction_isolation = 'read committed';
-}
-step "s2insert" {
-  INSERT INTO ctoast (key, val) VALUES (1, ctoast_large_val()) ON CONFLICT DO NOTHING;
-}
-
-session "s3"
-setup
-{
-  SET default_transaction_isolation = 'read committed';
-}
-step "s3insert" {
-  INSERT INTO ctoast (key, val) VALUES (1, ctoast_large_val()) ON CONFLICT DO NOTHING;
-}
-
-permutation "s2insert" "s3insert" "s1commit"