Re: Strangely Variable Query Performance

[Steve <cheetah@xxxxxxxxxx>]

Here's my planner parameters:

seq_page_cost = 1.0                     # measured on an arbitrary scale
random_page_cost = 1.5                  # same scale as above
cpu_tuple_cost = 0.001                  # same scale as above
cpu_index_tuple_cost = 0.0005           # same scale as above
cpu_operator_cost = 0.00025             # same scale as above
effective_cache_size = 8192MB

default_statistics_target = 100         # range 1-1000


On a machine with 16 gigs of RAM.  I tried to make it skew towards 
indexes.  However, even if I force it to use the indexes 
(enable_seqscan=off) it doesn't make it any faster really :/

Steve

On Thu, 12 Apr 2007, Tom Lane wrote:

> Scott Marlowe <smarlowe@xxxxxxxxxxxxxxxxx> writes:
> > So there's a misjudgment of the number of rows returned by a factor of
> > about 88.  That's pretty big.  Since you had the same number without the
> > receipt date (I think...) then it's the encounter_id that's not being
> > counted right.
>
> I don't think that's Steve's problem, though.  It's certainly
> misestimating, but nonetheless the cost estimate for the seqscan is
> 1902749.83 versus 14819.81 for the bitmap scan; it should've picked
> the bitmap scan anyway.
>
> I tried to duplicate the problem here, without any success; I get
>
> Bitmap Heap Scan on detail_summary ds  (cost=422.01..801.27 rows=100 width=4)
>   Recheck Cond: (encounter_id = ANY ('{8813186,8813187,8813188,8813189,8813190,8813191,8813192,8813193,8813194,8813195,8813196,8813197,8813198,8813199,8813200,8813201,8813202,8813203,8813204,8813205,8813206,8813207,8813208,8813209,8813210,8813211,8813212,8813213,8813214,8813215,8813216,8813217,8813218,8813219,8813220,8813221,8813222,8813223,8813224,8813225,8813226,8813227,8813228,8813229,8813230,8813231,8813232,8813233,8813234,8813235,8813236,8813237,8813238,8813239,8813240,8813241,8813242,8813243,8813244,8813245,8813246,8813247,8813248,8813249,8813250,8813251,8813252,8813253,8813254,8813255,8813256,8813257,8813258,8813259,8813260,8813261,8813262,8813263,8813264,8813265,8813266,8813267,8813268,8813269,8813270,8813271,8813272,8813273,8813274,8813275,8813276,8813277,8813278,8813279,8813280,8813281,8813282,8813283,8813284,8815534}'::integer[]))
>   Filter: (receipt >= '1998-12-30'::date)
>   ->  Bitmap Index Scan on detail_summary_encounter_id_idx  (cost=0.00..421.98 rows=100 width=0)
>         Index Cond: (encounter_id = ANY ('{8813186,8813187,8813188,8813189,8813190,8813191,8813192,8813193,8813194,8813195,8813196,8813197,8813198,8813199,8813200,8813201,8813202,8813203,8813204,8813205,8813206,8813207,8813208,8813209,8813210,8813211,8813212,8813213,8813214,8813215,8813216,8813217,8813218,8813219,8813220,8813221,8813222,8813223,8813224,8813225,8813226,8813227,8813228,8813229,8813230,8813231,8813232,8813233,8813234,8813235,8813236,8813237,8813238,8813239,8813240,8813241,8813242,8813243,8813244,8813245,8813246,8813247,8813248,8813249,8813250,8813251,8813252,8813253,8813254,8813255,8813256,8813257,8813258,8813259,8813260,8813261,8813262,8813263,8813264,8813265,8813266,8813267,8813268,8813269,8813270,8813271,8813272,8813273,8813274,8813275,8813276,8813277,8813278,8813279,8813280,8813281,8813282,8813283,8813284,8815534}'::integer[]))
>
> so either this has been fixed by a post-8.2.3 bug fix (which I doubt,
> it doesn't seem familiar at all) or there's some additional contributing
> factor.  Steve, are you using any nondefault planner parameters?
>
> 			regards, tom lane
>
> ---------------------------(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