From: Justin Pryzby <pryzby@telsasoft.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-performance@postgresql.org
Subject: Re: no MCV list of tiny table with unique columns
Date: Sat, 5 Nov 2016 17:36:37 -0500
Message-ID: <20161105223637.GJ2139@telsasoft.com> (raw)
In-Reply-To: <27252.1478130503@sss.pgh.pa.us>
References: <20161102185318.GA3987@telsasoft.com>
<26162.1478117146@sss.pgh.pa.us>
<20161102201955.GB2139@telsasoft.com>
<27252.1478130503@sss.pgh.pa.us>
List-Unsubscribe: <mailto:majordomo@postgresql.org?body=unsub%20pgsql-performance>
On Wed, Nov 02, 2016 at 07:48:23PM -0400, Tom Lane wrote:
> There's not a lot of point in worrying about your two-row table when these
> other estimates are off by multiple orders of magnitude. In this
> particular case my first bet would be that the planner has no idea about
> the selectivity of the conditions on "echo_tango('seven_november'::text,
> four_charlie)". Reformulating that, or maybe making an index on it just
> so that ANALYZE will gather stats about it, could help.
Thanks, you're exactly right. That's date_trunc('hour') BTW.
We actually already have a "new way" of doing that which avoids date_trunc, so
now I just have to get it in place for 100+ old reports..
I thought I had tried that before, but I think I was confusing myself, and
tried putting the index on the parent, which ends up with no stats since it's
empty.
With indices+analyze:
Sort (cost=189014.28..189014.28 rows=1 width=785) (actual time=25063.831..25063.886 rows=328 loops=1)
...
BTW:
join_collapse_limit | 8
from_collapse_limit | 8
..and changing them doesn't seem to have any effect. By my count there's 11
tables, not counting multiply a few used multiply..
Thanks again.
Justin
--
Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-performance
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: pryzby@telsasoft.com, tgl@sss.pgh.pa.us
Subject: Re: no MCV list of tiny table with unique columns
In-Reply-To: <20161105223637.GJ2139@telsasoft.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox