On Thu, Jul 24, 2008 at 7:06 PM, Stephen Frost <sfrost@xxxxxxxxxxx> wrote: > * John D. Burger (john@xxxxxxxxx) wrote: >> My understanding is that PG will use an index on the referring side of a >> foreign key for FK checks. How can I tell whether it's doing that? > > It should, when it makes sense, yes. Having the actual schema > definitions would help in debugging this, of course. > >> EXPLAIN ANALYZE just shows something like this: >> >> => explain analyze delete from segments where segmentid = 24305259; > > What does: > > explain analyze > delete from tokenizedSegments > where segmentId = 24305259; > > look like? If you're doing that put it in a begin; rollback; sandwich so your rows don't disappear while testing. Or just do a explain analyze select 1 from tokenizedSegments where segentId=23405259; the plan would be the same I'd think > > If more than a few percent of the tokenizedSegments table has a > segmentId of 24305259 then PG may rightly be scanning the whole table > sequantially because going through it randomly with an index would be > slower. There's a few options which can tune those parameters in the > planner, of course, but you might consider doing a test > 'set enable_seqscan = false;' first, if it's indeed doing one, to see > what the difference really is. > > Thanks, > > Stephen > > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v1.4.9 (GNU/Linux) > > iEYEARECAAYFAkiJJxIACgkQrzgMPqB3kighnACfd1AaKusTxFaKIqcqEjAmvRwm > LmwAnR0YegtP/rr84LiVVAMJUv3dYOMj > =dPu1 > -----END PGP SIGNATURE----- > >
