Re: Important speed difference between a query and a - Mailing list pgsql-performance

From Tom Lane
Subject Re: Important speed difference between a query and a
Date
Msg-id 14131.1051199816@sss.pgh.pa.us
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In response to Re: Important speed difference between a query and a  (Frederic Jolliton <fred-pg@jolliton.com>)
Responses Re: Important speed difference between a query and a  (Frederic Jolliton <fred-pg@jolliton.com>)
List pgsql-performance
Frederic Jolliton <fred-pg@jolliton.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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