Home > mailing lists

Re: unoptimized nested loops - Mailing list pgsql-general

From	Jeff Janes
Subject	Re: unoptimized nested loops
Date	June 2, 2022 07:05:46
Msg-id	CAMkU=1whHwiBkt4t4e8Y85NT_ReLyo-qjvdpOROuW2N7dQCSug@mail.gmail.com Whole thread Raw
In response to	unoptimized nested loops (Tim Kelly <gtkelly@dialectronics.com>)
Responses	Re: unoptimized nested loops (Tom Lane <tgl@sss.pgh.pa.us>)
List	pgsql-general

On Tue, May 31, 2022 at 4:04 PM Tim Kelly <gtkelly@dialectronics.com> wrote:

c_db=>select count(id) from metadata where author like '%Kelly%';

count
-------
3558
(1 row)

It would be interesting to see the explain of this. We know how many rows it found, but not how many it thinks it will find.

I do not see evidence that the nested loop is trying to reduce overhead
by using the smaller set. It seems to want to scan on data first either
way.

The planner probably doesn't know which one is smaller.

I have run vacuum analyze, in the hopes that the optimizer is
miscalculating, to no avail.

What version are you using?

Cheers,

Jeff

From: David Rowley
Date: 02 June 2022, 00:10:07
Subject: Re: unoptimized nested loops

From: Tom Lane
Date: 02 June 2022, 07:32:40
Subject: Re: unoptimized nested loops