Re: Worse perfomance on 8.2.0 than on 7.4.14

> I have a simple query which uses 32ms on 7.4.14 and 1015ms on 8.2.0.
> I guess 7.4.14 creates a better execution plan than 8.2.0 for this query but
> i don't know how to get it to select a better one.
> Explain analyse output will be found near the end of the e-mail.
>
> Explain analyze is run several times to get a stable result
> so i guess the numbers presented is with as much as possible
> data in memory buffers.
>
> Query: "select * from view_subset;" run against 7.4.14 server.
> QUERY PLAN
> ------------------------------------------------------------------------
> Nested Loop (cost=0.00..1400.86 rows=17 width=8) (actual time=0.161..26.287 rows=68 loops=1)
> -> Index Scan using uut_result_subset_start_date_time_idx on uut_result_subset ur (cost=0.00..63.28 rows=18 width=4) (actual time=0.052..0.195 rows=68 loops=1)
> Index Cond: (start_date_time > '2006-12-11 00:00:00'::timestamp without time zone)
> -> Index Scan using step_result_uut_result_idx on step_result_subset sr (cost=0.00..74.28 rows=2 width=8) (actual time=0.149..0.379 rows=1 loops=68)
> Index Cond: ("outer".id = sr.uut_result)
> Filter: (step_parent = 0)
> Total runtime: 26.379 ms
>
> Query: "select * from view_subset;" run against 8.4.0 server.
>
> QUERY PLAN
> ----------------------------------------------------------------------
> Hash Join (cost=339.61..77103.61 rows=96 width=8) (actual time=5.249..1010.669 rows=68 loops=1)
> Hash Cond: (sr.uut_result = ur.id)
> -> Index Scan using step_result_subset_parent_key on step_result_subset sr (cost=0.00..76047.23 rows=143163 width=8) (actual time=0.082..905.326 rows=176449 loops=1)
> Index Cond: (step_parent = 0)
> -> Hash (cost=339.31..339.31 rows=118 width=4) (actual time=0.149..0.149 rows=68 loops=1)
> -> Bitmap Heap Scan on uut_result_subset ur (cost=4.90..339.31 rows=118 width=4) (actual time=0.060..0.099 rows=68 loops=1)
> Recheck Cond: (start_date_time > '2006-12-11 00:00:00'::timestamp without time zone)
> -> Bitmap Index Scan on uut_result_subset_start_date_time_idx (cost=0.00..4.90 rows=118 width=0) (actual time=0.050..0.050 rows=68 loops=1)
> Index Cond: (start_date_time > '2006-12-11 00:00:00'::timestamp without time zone)
> Total runtime: 1010.775 ms

Did you lower random_page_cost in 8.2 (which defaults to 4.0)? If not try 2.

regards
Claus