On Mon, Oct 27, 2014 at 08:24:15AM -0400, Robert Haas wrote: > On Sat, Oct 25, 2014 at 2:00 PM, Noah Misch <n...@leadboat.com> wrote: > >> http://www.postgresql.org/message-id/ca+tgmoy4glsxzk0tao29-ljtcuj0sl1xwcwq51xb-hfysgi...@mail.gmail.com > >> http://www.postgresql.org/message-id/20893.1393892...@sss.pgh.pa.us > >> http://www.postgresql.org/message-id/20140306224340.ga3551...@tornado.leadboat.com > >> > >> As far as triggers are concerned, the issue of skew between the > >> transaction snapshot and what the ruleutils.c snapshots do seems to be > >> the principal issue. Commit e5550d5fec66aa74caad1f79b79826ec64898688 > >> changed pg_get_constraintdef() to use an MVCC snapshot rather than a > >> current MVCC snapshot; if that change is safe, I am not aware of any > >> reason why we couldn't change pg_get_triggerdef() similarly. > > > > pg_get_triggerdef() is fine as-is with concurrent CREATE TRIGGER. The > > pg_get_constraintdef() change arose to ensure a consistent result when > > concurrent ALTER TABLE VALIDATE CONSTRAINT mutates a constraint definition. > > (Reducing the lock level of DROP TRIGGER or ALTER TRIGGER, however, would > > create the analogous problem for pg_get_triggerdef().) > > Maybe so, but I'd favor changing it anyway and getting it over with. > The current situation seems to have little to recommend it; moreover, > it would be nice, if it's possible and safe, to weaken the lock levels > for all three of those commands at the same time. Do you see any > hazards for ALTER or DROP that do not exist for CREATE?
ALTER TRIGGER is not bad; like you say, change pg_get_triggerdef_worker() the way commit e5550d5 changed pg_get_constraintdef_worker(). DROP TRIGGER is more difficult. pg_constraint.tgqual of a dropped trigger may reference other dropped objects, which calls for equipping get_rule_expr() to use the transaction snapshot. That implicates quite a bit of ruleutils.c code. -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
