I got a problem with the performance of a PL/PGsql stored procedure outputting an xml.
Server version: PostgreSQL 8.3.6 on i686-pc-linux-gnu, compiled by GCC gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-46)
CPU: Intel(R) Core(TM) i3 CPU 540 @ 3.07GHz
RAM installed: 4GB
Hard Disk: Seagate 500Gb SATA 2
This is a simplified content of the function showing the xmlconcat behaviour.
CREATE OR REPLACE FUNCTION test_function (v_limit int)
RETURNS xml AS
$BODY$
DECLARE
v_xml xml;
BEGIN
FOR i IN 1..v_limit LOOP
v_xml := xmlconcat(v_xml, xmlelement(name content, 'aaaaaaa'));
END LOOP;
RETURN v_xml ;
END
$BODY$
LANGUAGE 'plpgsql' SECURITY DEFINER ;
As long as the v_limit parameter grows (and then the size of the output xml, the time needed increase exponentially.
Look at this examples:
pang=# explain analyze select test_function(1000);
QUERY PLAN
--------------------------------------------------------------------------------------
Result (cost=0.00..0.26 rows=1 width=0) (actual time=65.430..65.431 rows=1 loops=1)
Total runtime: 65.457 ms
(2 rows)
pang=# explain analyze select test_function(5000);
QUERY PLAN
----------------------------------------------------------------------------------------
Result (cost=0.00..0.26 rows=1 width=0) (actual time=473.318..473.318 rows=1 loops=1)
Total runtime: 473.340 ms
(2 rows)
pang=# explain analyze select test_function(15000);
QUERY PLAN
------------------------------------------------------------------------------------------
Result (cost=0.00..0.26 rows=1 width=0) (actual time=4044.903..4044.904 rows=1 loops=1)
Total runtime: 4044.928 ms
(2 rows)
pang=# explain analyze select test_function(50000);
QUERY PLAN
--------------------------------------------------------------------------------------------
Result (cost=0.00..0.26 rows=1 width=0) (actual time=94994.337..94994.369 rows=1 loops=1)
Total runtime: 94994.396 ms
(2 rows)
I already tried to update to 8.3.23 service version but i didn't see any improvement.
Do you have any suggestion about how to increase the performance of xmlconcat?
My need is to use stored procedures that calls xmlconcat more than 50000 times, but it is unacceptable 94 seconds to complete the job.
Thanks in advance