Re: function optimization ???

Brent Verner <brent@rcfile.org> writes:
> calling it as:
>   SELECT p.*, p.book_info.title FROM pricing p WHERE vista_ans='POD';
> background and observation:
>   the pricing table is fairly large, but only a small number meet
>   "WHERE vista_ans='POD'". I can select all where vista_ans='POD'
>   very quickly (.2 sec), but adding in the get_book(pricing) call
>   slows this down to about 20sec. I can, with an external sql query,
>   select all of the desired records in about 1 sec, so it appears
>   to me that the function is being called regardless of whether
>   or not the WHERE clause is being satisfied.

This conclusion is absolutely false: the SELECT target list is NOT
evaluated except at rows where the WHERE condition is satisfied.

I suspect the real problem is that the select inside the function
is not being done as efficiently as you'd like.  How big is
catalog_general, and would a sequential scan over it inside the
function account for the performance discrepancy?

IIRC, 7.0.* is not very bright about using indexscans in situations
where the righthand side of the WHERE clause is anything more complex
than a literal constant or simple parameter reference ($n).  The
fieldselect you have here would be enough to defeat the indexscan
recognizer.  This is fixed in 7.1, however.  For now, you could
declare book_info as taking a simple datum and invoke it asp.vista_isbn.book_info.title

BTW, star_isbn and vista_isbn are the same datatype, I trust, else
that might cause failure to use an indexscan too.
        regards, tom lane