From: | "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> |
---|---|
To: | "Robert Haas" <robertmhaas(at)gmail(dot)com>, "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: So, is COUNT(*) fast now? |
Date: | 2011-10-24 17:38:34 |
Message-ID: | 4EA55C4A02000025000424D5@gw.wicourts.gov |
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Lists: | pgsql-hackers |
Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> I had wondered whether it'd be worth optimizing that along the
> lines of slot_getallattrs(). But most indexes probably have only
> one column, or anyway not enough to make for a useful savings.
>From a heavily-used production database:
cir=> select indnatts, count(*) from pg_index group by indnatts
order by indnatts;
indnatts | count
----------+-------
1 | 200
2 | 684
3 | 155
4 | 76
5 | 43
6 | 13
7 | 2
9 | 1
(8 rows)
This includes system table and TOAST table indexes (which seem to
have two columns). There are over 400 user tables, each of which
has a primary key, so most primary keys in our database are more
than one column.
-Kevin
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