Hi, I have PostgreSQL 9.0.12 on Windows. I have some simple function: CREATE OR REPLACE FUNCTION sfunction() RETURNS BOOL AS $BODY$ DECLARE q TEXT; r RECORD; BEGIN q='SELECT 1 from tb_klient LIMIT 0'; FOR r IN EXECUTE q LOOP END LOOP; RETURN NULL; RETURN NULL; END; $BODY$ LANGUAGE 'plpgsql'; And some simple Query: explain analyze SELECT sfunction() AS value FROM ( SELECT 5604913 AS id ,5666 AS idtowmag ) AS c LEFT OUTER JOIN tg_tm AS tm ON (tm.ttm_idtowmag=c.idtowmag); When I run this query explain analyze is: Subquery Scan on a (cost=0.00..0.27 rows=1 width=8) (actual time=24.041..24.042 rows=1 loops=1) -> Result (cost=0.00..0.01 rows=1 width=0) (actual time=0.001..0.002 rows=1 loops=1) "Total runtime: 24.068 ms" But when I change: 1. Table tb_klient to some other table (but not any other – queries with some tables are still slow) or 2. “FOR r IN EXECUTE q” 3. add “LEFT OUTER JOIN tb_klient AS kl ON (kl.k_idklienta=c.idtowmag)” to query Explain analyze of query is: "Subquery Scan on a (cost=0.00..0.27 rows=1 width=8) (actual time=1.868..1.869 rows=1 loops=1)" " -> Result (cost=0.00..0.01 rows=1 width=0) (actual time=0.002..0.002 rows=1 loops=1)" "Total runtime: 1.894 ms" Explain analyze of “SELECT 1 from tb_klient LIMIT 0” is: "Limit (cost=0.00..0.13 rows=1 width=0) (actual time=0.001..0.001 rows=0 loops=1)" " -> Seq Scan on tb_klient (cost=0.00..854.23 rows=6823 width=0) (never executed)" "Total runtime: 0.025 ms" tb_klient has 8200 rows and 77 cols. Why speed of executing (or planning) some very simple query from string in pl/pgsql is dependent from whole query or why “FOR r IN EXECUTE q” is significally slower from “FOR r IN query”? ------------------------------------------- Artur Zajac |
