Subject: Re: [SQL] OFFSET impact on Performance???
From: Ragnar =?ISO-8859-1?Q?Hafsta=F0?= <gnari@simnet.is>
To: pgsql-performance@postgresql.org
Cc: Andrei Bintintan <klodoma@ar-sd.net>, pgsql-sql@postgresql.org
In-Reply-To: <87pt00c9zd.fsf@stark.xeocode.com>
References: <019f01c4fee1$1b58d600$0b00a8c0@forge>
	<41EF9FD3.5020400@archonet.com> <020d01c4fef6$595bb9d0$0b00a8c0@forge>
	<87pt00c9zd.fsf@stark.xeocode.com>
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Date: Thu, 20 Jan 2005 19:12:06 +0000
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On Thu, 2005-01-20 at 11:59 -0500, Greg Stark wrote:

> The best way to do pages for is not to use offset or cursors but to use an
> index. This only works if you can enumerate all the sort orders the
> application might be using and can have an index on each of them.
> 
> To do this the query would look something like:
> 
> SELECT * FROM tab WHERE col > ? ORDER BY col LIMIT 50
> 
> Then you take note of the last value used on a given page and if the user
> selects "next" you pass that as the starting point for the next page.

this will only work unchanged if the index is unique. imagine , for
example if you have more than 50 rows with the same value of col.

one way to fix this is to use ORDER BY col,oid

gnari