Hello Matthias, 2011/3/29 Matthias Kestenholz <m...@spinlock.ch>
> On Tue, Mar 29, 2011 at 2:27 PM, Fabian Büchler > <fabian.buech...@gmail.com> wrote: > > I've analyzed the query using pgAdmin and it seems the most time is being > > spent with a the GroupAggregate. > > This is because of so many columns being listed in the GROUP BY clause. > > Creating two-column indexes over event_id and date or some other > > combinations I've tried did not gain any perforamance. > > > > Thus I've tried to get rid of some by just selecting some columns via > > "only(...)". Strangely this does not have any effect on the GROUP BY > clause. > > > > only() does not affect the generated query in any way -- it would be a > bug if it did. > only() does affect the selected columns, but of course that can never affect the rows that will be selected. > > On the other hand, if I use "values(...)" the GROUP BY clause shrinks to > > only the named columns (but still being listed twice each). > > > > There's already a ticket for the duplicated GROUP BY columns in the > Django ticket tracker: > > http://code.djangoproject.com/ticket/15709 > Thanks for this insight. The bug is already fixed but not yet checked in. Good to know. > > The QuerySet.only() method not limiting the GROUP BY clause to the named > > columns seems like a "bug" (or inefficiency) in the ORM to me. Is that > valid > > at any rate? > > > > Not sure about that. I'd say it isn't a bug because this could > potentially cause different results depending on the table and table > content. > Interesting thought. I guess that might be true, although I'm not quite enough SQL-sawy to be able to evaluate if that is correct. In my case the massive GROUP BY clause caused a pretty severe impact on query speed. But by now I've fixed the problem by just using the QuerySet.values() method instead of .only(). That works just fine and fast. > Matthias > Regards, Fabian > -- > Django CMS building toolkit: > http://www.feinheit.ch/labs/feincms-django-cms/ > -- You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-users@googlegroups.com. To unsubscribe from this group, send email to django-users+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/django-users?hl=en.
