Earlier this week, we got an error applying an EXECUTE SCRIPT on the
slave commands with an UPDATE command in the script.  The script
looked like:

ALTER TABLE ua_users ADD COLUMN is_spider VARCHAR(1);
UPDATE ua_users SET is_spider = ''N'';
UPDATE ua_users SET is_spider = ''Y'' WHERE login_id LIKE ''webtest_'';
ALTER TABLE ua_users ALTER is_spider SET DEFAULT ''N'';
ALTER TABLE ua_users ADD CONSTRAINT ck_is_spider CHECK (is_spider IN
(''Y'', ''N''));
ALTER TABLE ua_users ALTER is_spider SET NOT NULL;

ALTER TABLE ua_users ADD COLUMN is_internal VARCHAR(1);
UPDATE ua_users SET is_internal = ''N'';
UPDATE ua_users SET is_internal = ''Y'' WHERE email_address LIKE
''%rentrak.com'';
ALTER TABLE ua_users ALTER is_internal SET DEFAULT ''N'';
ALTER TABLE ua_users ADD CONSTRAINT ck_is_internal CHECK (is_internal
IN (''Y'', ''N''));
ALTER TABLE ua_users ALTER is_internal SET NOT NULL;

Basically, add a new column, populate it with the UPDATE, and then add
constraints.  It failed on both slaves with:

PGRES_FATAL_ERROR ERROR:  could not find trigger 946964630.

That trigger is part of a foreign key between ua_users and
ua_subscriptions.  It is the trigger on the ua_subscriptions table. 
Both tables are replicated in the same set so I would expect that the
EXECUTE SCRIPT command would restore the foreign key triggers on both
tables.  We have had a similar errors when doing UPDATEs in EXECUTE
SCRIPT for similar scripts.

I fixed the problem by modifying the DDL_SCRIPT event to just add the
tables, ran the UPDATE normally, and then made the constraints in a
separate execute script.

 - Ian