Re: Order by optimisations?

From: Christopher Kings-Lynne <chriskl(at)familyhealth(dot)com(dot)au>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Hannu Krosing <hannu(at)skype(dot)net>, Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Order by optimisations?
Date: 2005-07-15 05:42:38
Message-ID: 42D74CCE.3030609@familyhealth.com.au
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> Well, date evidently isn't the high-order key of this index. But why
> exactly are you worried about a sort of 2 rows?

Aha that's nailed it:

usa=> explain select * from users_myfoods_map where user_id=1 and date
between '2003-11-03' and '2003-11-03' order by user_id, date;
QUERY PLAN

-------------------------------------------------------------------------------------------------------------
Index Scan using users_myfoods_map_user_id_date_key on
users_myfoods_map (cost=0.00..3.78 rows=1 width=22)
Index Cond: ((user_id = 1) AND (date >= '2003-11-03'::date) AND
(date <= '2003-11-03'::date))
(2 rows)

I don't care about this particular result. But imagine it running
thousands of times a minute, with result sets between 0 and 50 rows...

Chris

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