On Wed, May 28, 2014 at 08:39:32PM +1200, David Rowley wrote: > The attached patch allows join removals for both sub queries with left > joins and also semi joins where a foreign key can prove the existence of > the record.
When a snapshot can see modifications that queued referential integrity triggers for some FK constraint, that constraint is not guaranteed to hold within the snapshot until those triggers have fired. For example, a query running within a VOLATILE function f() in a statement like "UPDATE t SET c = f(c)" may read data that contradicts FK constraints involving table "t". Deferred UNIQUE constraints, which we also do not yet use for deductions in the planner, have the same problem; see commit 0f39d50. This project will need a design accounting for that hazard. As a point of procedure, I recommend separating the semijoin support into its own patch. Your patch is already not small; delaying non-essential parts will make the essential parts more accessible to reviewers. Thanks, nm -- Noah Misch EnterpriseDB http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
