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Date: Sun, 28 Sep 2003 09:21:33 -0700
From: Joe Conway <mail@joeconway.com>
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To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Josh Berkus <josh@agliodbs.com>,
	Richard Sydney-Smith <richard@ibisaustralia.com>, pgsql-sql@postgresql.org
Subject: Re: Mystery function error
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	<200309272229.50601.josh@agliodbs.com>
	<9398.1064765182@sss.pgh.pa.us>
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Tom Lane wrote:
> Josh Berkus <josh@agliodbs.com> writes:
>>Also, this will run faster if you do it as a SQL function:
> 
>>CREATE FUNCTION locate ( text, text ) RETURNS INT AS '
>>SELECT POSITION($2, $1);
>>' LANGUAGE SQL IMMUTABLE STRICT;
> 
> This is definitely the solution I'd recommend for 7.4 (because 7.4 would
> inline the SQL function definition, resulting in zero runtime overhead).
> In 7.3 I suspect the plpgsql version might be a tad faster, or anyway
> comparable.  Has anyone done any head-to-head performance comparisons
> on such simple functions?
> 

I did a quick check last night on 7.3.4 and found that plpgsql was faster:

CREATE OR REPLACE FUNCTION public.locate(bpchar, bpchar) RETURNS int4 AS '
   -- search for the position of $2 in $1
   declare
     srcstr alias for $1;
     searchstr alias for $2;
   begin
     return position(searchstr in srcstr);
   end;
' LANGUAGE 'plpgsql' IMMUTABLE;

regression=# explain analyze select locate('abc','b');

                                     QUERY PLAN
----------------------------------------------------------------------------------
  Result  (cost=0.00..0.01 rows=1 width=0) (actual time=0.01..0.01 
rows=1 loops=1)
  Total runtime: 0.03 msec
(2 rows)

DROP FUNCTION public.locate(bpchar, bpchar);
CREATE OR REPLACE FUNCTION public.locate(bpchar, bpchar) RETURNS int4 AS '
   select position($2 in $1)
' LANGUAGE 'sql';
regression=# explain analyze select locate('abc','b');
                                     QUERY PLAN
----------------------------------------------------------------------------------
  Result  (cost=0.00..0.01 rows=1 width=0) (actual time=0.24..0.24 
rows=1 loops=1)
  Total runtime: 0.26 msec
(2 rows)


On 7.4 (different hardware), I get this:

plpgsql
--------
regression=# explain analyze select locate('abc','b');
                                     QUERY PLAN
----------------------------------------------------------------------------------
  Result  (cost=0.00..0.01 rows=1 width=0) (actual time=0.00..0.00 
rows=1 loops=1)
  Total runtime: 0.05 msec
(2 rows)

sql
--------
regression=# explain analyze select locate('abc','b');
                                     QUERY PLAN
----------------------------------------------------------------------------------
  Result  (cost=0.00..0.01 rows=1 width=0) (actual time=0.01..0.01 
rows=1 loops=1)
  Total runtime: 0.03 msec
(2 rows)


Joe