> 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

---------------------------(end of broadcast)---------------------------
TIP 6: explain analyze is your friend

--- Claus Guttesen <kometen@gmail.com> skrev:

> > 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.

Thanks for the suggestion, but it was no change of
result.

> regards
> Claus


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---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match