Re: Trivial function query optimized badly

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От Craig A. James
Тема Re: Trivial function query optimized badly
Дата
Msg-id 459CA541.3060009@modgraph-usa.com
обсуждение исходный текст
Ответ на Re: Trivial function query optimized badly  (Tom Lane <tgl@sss.pgh.pa.us>)
Список pgsql-performance
Tom Lane wrote:
> "Craig A. James" <cjames@modgraph-usa.com> writes:
>>   CREATE OR REPLACE FUNCTION cansmiles(text) RETURNS text
>>   AS '/usr/local/pgsql/lib/libchem.so', 'cansmiles'
>>   LANGUAGE 'C' STRICT IMMUTABLE;
>
> Umm ... this is a single-argument function.
>
>> db=> explain analyze select version_id, 'Brc1ccc2nc(cn2c1)C(=O)O' from version where version.isosmiles =
cansmiles('Brc1ccc2nc(cn2c1)C(=O)O',1); 
>
> And this query is invoking some other, two-argument function; which
> apparently hasn't been marked IMMUTABLE, else it'd have been folded
> to a constant.

Good catch, mystery solved.  There are two definitions for this function, the first just a "wrapper" for the second
withthe latter parameter defaulting to "1".  The second definition was missing the "IMMUTABLE" keyword. 

Thanks!
Craig

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