On 2017-02-24 15:18:04 -0800, Andres Freund wrote: > On 2017-02-24 15:12:37 -0800, Andres Freund wrote: > > On 2017-02-24 18:04:18 -0500, Tom Lane wrote: > > > Concretely, something like the attached. This passes regression tests > > > but I've not pushed on it any harder than that. > > > > Heh, I'd just gotten something that didn't immediately crash anymore ;) > > > > Running your patch against Jeff's test-case, verified before that I > > could easily reproduce the O(N^2) cost. > > Oh, that didn't take as long as I was afraid (optimized/non-assert build): > > postgres[26268][1]=# SET work_mem = '13GB'; > SET > Time: 2.591 ms > postgres[26268][1]=# select count(*) from foobar2 where not exists (select 1 > from foobar t where t.titleid=foobar2.titleid); > Time: 268043.710 ms (04:28.044)
As another datapoint, I measured this patch against the problem from https://www.postgresql.org/message-id/20170227111732.vrx5v72ighehw...@alap3.anarazel.de (see top post in thread), and it indeed fixes the runtime issue - there's still considerably higher memory usage and some runtime overhead, but the quadratic behaviour is gone. I think we should go forward with something like this patch in all branches, and only use Tomas' patch in master, because they're considerably larger. Regards, Andres -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
