Re: select distinct runs slow on pg 10.6

From: Justin Pryzby <pryzby(at)telsasoft(dot)com>
To: yash mehta <yash215(at)gmail(dot)com>
Cc: pgsql-performance(at)lists(dot)postgresql(dot)org
Subject: Re: select distinct runs slow on pg 10.6
Date: 2019-09-09 10:39:30
Message-ID: 20190909103930.GP7201@telsasoft.com
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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

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