Re: select distinct runs slow on pg 10.6
Flo Rance <[email protected]>
| Newsgroups | gmane.comp.db.postgresql.performance |
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| Message-ID | <CAHogYcWfhsT=6XmLOX2MKV9QF8GQQsD+BBxh0uXxLCyT5XL_4Q@mail.gmail.com> |
There are few things to consider: - you don't need to use distinct on all columns (and therefore sort all columns) - you should try to sort in memory, better than on-disk - it seems that the planner doesn't predict the good number of rows Regards, Florian On Mon, Sep 9, 2019 at 12:46 PM Justin Pryzby <[email protected]> wrote: > On Mon, Sep 09, 2019 at 02:00:01PM +0530, yash mehta wrote: > > We have a query that takes 1min to execute in postgres 10.6 and the same > > executes in 4 sec in Oracle database. The query is doing 'select > distinct'. > > If I add a 'group by' clause, performance in postgres improves > > significantly and fetches results in 2 sec (better than oracle). But > > unfortunately, we cannot modify the query. Could you please suggest a way > > to improve performance in Postgres without modifying the query. > > Not sure it helps, but I remember this: > > https://www.postgresql.org/message-id/CAKJS1f9q0j3BgMUsDbtf9%3DecfVLnqvkYB44MXj0gpVuamcN8Xw%40mail.gmail.com > > >