Re: Important speed difference between a query and a

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Frederic Jolliton <fred-pg(at)jolliton(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Important speed difference between a query and a
Date: 2003-04-24 15:56:56
Message-ID: 14131.1051199816@sss.pgh.pa.us
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Frederic Jolliton <fred-pg(at)jolliton(dot)com> writes:
>> To "emulate" a parametred view, I created a function as follow:
>>
>> CREATE FUNCTION get_info (integer) RETURNS SETOF type_get_info
>> AS '...' <- here the query show below, where 'LIMIT $1' is used instead of 'LIMIT 10'
>> LANGUAGE sql;

> So, the query in the function is not using index but the exact same
> query alone does !

But it's not the same query, is it? With "LIMIT $1" the planner can't
know what the limit value is exactly, so it has to generate a plan that
won't be too unreasonable for either a small or a large limit.

regards, tom lane

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