Arnaud, Have you run "ANALYZE" on the table after creating index? Also make sure that "#effective_cache_size" is set properly. A higher value makes it more likely to use index scans. Thanks asif ali
Arnaud Lesauvage <[EMAIL PROTECTED]> wrote: Ragnar a écrit : > On mið, 2006-12-13 at 14:38 +0100, Arnaud Lesauvage wrote: >> Jens Schipkowski a écrit : >> > On Wed, 13 Dec 2006 13:23:41 +0100, Arnaud Lesauvage >> >> Why is this query better than the other one ? Because it runs the >> >> "(field IN ('some','other') AND field2 = 'Y')" once and then executes >> >> the join with the resulting set ? >> > True. The Subselect in FROM clause will be executed once and will be >> > joined using the condition at where clause. So your condition at t2 is not >> > >> > executed for each row in t1(2mio records) but for each row in t2(1k >> > records). And the boolean value is already set during update. >> >> OK Jens, thanks for clarifying this. >> I thought the planner could guess what to do in such cases. > > don't worry, it will. > this is not your problem Indeed, the new query does not perform that well : "Hash Join (cost=112.75..307504.97 rows=2024869 width=355) (actual time=53.995..246443.811 rows=2020061 loops=1)" " Hash Cond: ("outer".uid = "inner".uid)" " -> Seq Scan on t1 (cost=0.00..261792.01 rows=2033001 width=338) (actual time=19.342..234304.499 rows=2033001 loops=1)" " -> Hash (cost=110.20..110.20 rows=1020 width=53) (actual time=4.853..4.853 rows=1020 loops=1)" " -> Seq Scan on t2 (cost=0.00..110.20 rows=1020 width=53) (actual time=0.017..2.586 rows=1020 loops=1)" "Total runtime: 2777844.892 ms" I removed all unnecessary indexes on t1 before running the query (I left the index on uid and the multicolumn index containind the updated field). I believe the multicolumn-functional-index computation is taking some time here, isn't it ? Regards -- Arnaud ---------------------------(end of broadcast)--------------------------- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate --------------------------------- Any questions? Get answers on any topic at Yahoo! Answers. Try it now.