Does FK Constraint help to improve performance? Or it is only for maintaining data integrity?
On Thu, Dec 13, 2012 at 7:38 PM, Claudio Freire <klaussfre...@gmail.com>wrote: > On Thu, Dec 13, 2012 at 8:50 PM, Evgeny Shishkin <itparan...@gmail.com> > wrote: > >>> OP joins 8 tables, and i suppose join collapse limit is set to default > 8. I thought postgresql's optimiser is not mysql's. > >> > >> It's not obvious to me that there's anything very wrong with the plan. > >> An 8-way join that produces 150K rows is unlikely to run in milliseconds > >> no matter what the plan. The planner would possibly have done the last > >> join step differently if it had had a better rowcount estimate, but even > >> if that were free the query would still have been 7 seconds (vs 8.5). > >> > > > > May be in this case it is. I once wrote to this list regarding similar > problem - joining 4 tables, result set are off by 2257 times - 750ms vs > less then 1ms. Unfortunately the question was not accepted to the list. > > > > I spoke to Bruce Momjian about that problem on one local conference, he > said shit happens :) > > I think it's more likely a missing FK constraint. >
