On 05/06/14 19:39, Tom Lane wrote: > Merlin Moncure <mmonc...@gmail.com> writes: >> On Thu, Jun 5, 2014 at 9:54 AM, Linos <i...@linos.es> wrote: >>> What I don't understand is why the statistics have this bad information, >>> all my tests are done on a database just restored and analyzed. Can I do >>> something to improve the quality of my database statistics and let the >>> planner do better choices? Maybe increase the statistics target of the >>> columns involved? >> By that I meant row count estimates coming out of the joins are way >> off. This is pushing the planner into making bad choices. The most >> pervasive problem I see is that the row count estimate boils down to >> '1' at some juncture causing the server to favor nestloop/index scan >> when something like a hash join would likely be more appropriate. > There's some fairly wacko stuff going on in this example, like why > is the inner HashAggregate costed so much higher by 9.3 than 8.4, > when the inputs are basically the same? And why does 9.3 fail to > suppress the SubqueryScan on "ven", when 8.4 does get rid of it? > And why is the final output rows estimate so much higher in 9.3? > That one is actually higher than the product of the two nestloop > inputs, which looks like possibly a bug. > > I think what's happening is that 9.3 is picking what it knows to be a less > than optimal join method so that it can sort the output by means of the > ordered scan "Index Scan using referencia_key on modelo mo", and thereby > avoid an explicit sort of what it thinks would be 42512461 rows. With a > closer-to-reality estimate there, it would have gone for a plan more > similar to 8.4's, ie, hash joins and then an explicit sort. > > There is a lot going on in this plan that we haven't been told about; for > instance at least one of the query's tables seems to actually be a view, > and some other ones appear to be inheritance trees with partitioning > constraints, and I'm suspicious that some of the aggregates might be > user-defined functions with higher than normal costs. > > I'd like to see a self-contained test case, by which I mean full details > about the table/view schemas; it's not clear whether the actual data > is very important here. > > regards, tom lane
Query 2 doesn't use any view and you can find the schema here: http://pastebin.com/Nkv7FwRr Query 1 use 5 views: ticket_cabecera, ticket_linea, reserva_cabecera, reserva_linea and tarifa_proveedor_modelo_precio, I have factored out the four first with the same result as before, you can find the new query and the new plan here: http://pastebin.com/7u2Dkyxp http://explain.depesz.com/s/2V9d Actually the execution time is worse than before. About the last view if I change join from tarifa_proveedor_modelo_precio to tarifa_modelo_precio (a table with nearly the same structure as the view) the query is executed much faster, but I get a similar time changing the (MIN(cab.time_stamp_recepcion)::DATE = ....) to (WHERE cab.time_stamp_recepcion::date = ....) in the "ent" subquery that never was a view. Anyway I included tarifa_modelo_precio to the query1 schema file for reference and you can find the plan using tarifa_modelo_precio instead of the view tarifa_proveedor_modelo_precio here: http://explain.depesz.com/s/4gV query1 schema file: http://pastebin.com/JpqM87dr Regards, Miguel Angel. -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
