Re: Performance question

On Tue, 11 Sep 2001, Stephan Szabo wrote:

> Well, the index isn't used because it estimates (apparently
> correctly) that not using it is cheaper.  Because the information about
> whether a row is valid is kept in the heap, for each index hit, the
> heap needs to be read to see if the row is visible.  This results in
> jumping about the heap file with seeks and such plus the index
> search itself.  When most of the rows are going to be returned, the
> sequence scan will generally be cheaper.
It would me drive crazy if this "cheaper" solution would last miore than
30 seconds for PostgreSQL if MS-SQL server solves this tasks in less
than a second.  This would really destroy all my plans with PostgreSQL
if it would be true (what I can´t really imagine).

> Alot of the real time may be being spent in the sort step.  You may want
> to raise the amount of memory used for sorting and see if that helps.
How to raise this memory amount.
This is more or less a theoretical question because sorting of about
150 items can´t last 30s.  The result set is:


MeldeKategorie    Anz
ADV    142
BOR    1
BRU    10
CAM    34965
CHL    45
CJK    61
CLO    6
COX    237
CRY    645
ECH    269
ECO    3030
EHC    750
FRT    1
FSV    160
GIL    3013
HAV    1495
HBV    3352
HCV    7710
HDV    18
HEV    33
HFA    24
HIN    66
HIV    3628
HTV    132
HXV    3
INV    2400
LEG    203
LEP    17
LIS    167
MSV    5164
MYL    2
MYT    4650
NEI    576
NWV    6566
PLA    692
POV    4
RBV    1
RIC    2
RTV    42862
RUB    1
SAL    47829
SHI    917
SPA    33
STY    60
TOX    26
TRI    6
TRP    674
VCH    2
YEN    4810


There is not much to sort here, thought.

Kind regards

        Andreas.