Re: Use of index in 7.0 vs 6.5

Tom Lane wrote:

> "Hiroshi Inoue" <Inoue(at)tpf(dot)co(dot)jp> writes:
> >> One way to put a thumb on the scales is to reduce the value of the SET
> >> variable random_page_cost. The default value is 4.0, which seems to
> >> correspond more or less to reality, but reducing it to 3 or so would
> >> shift the planner pretty nicely in the direction of indexscans.

This worked great! Is their a place I can change the default to 3?
I do not want to change all the scripts to include this :)

> > Or how about changing current fudge factor ?
> > For example,from 0.5 to 0.2 which is the fudge factor of attdisbursion
> > calculation.
>
> Yes, that's another way --- and probably more defensible than changing
> random_page_cost, now that I think about it. Unfortunately it's a
> hardwired constant and so not as easily experimented with :-(.
>
> regards, tom lane

Can you give me more information about this? I do not have a problem
re-compiling the database and performing more testing if you would like.

Tom,

To answer your question in a previous post:
Since you find that in reality the indexscan method is very quick,
I'm guessing that there are actually fairly few tuples matching
host_id = 404. Could you run a quick "select count(*)" to check?

procman=# select count(*) from medusa where host_id = 404;
count
-------
680
(1 row)

procman=# select count(catagory) from medusa where host_id = 404 and
catagory like 'A%';
count
-------
4
(1 row)

Thanks again everyone for all the help! Now that I am finished with school
for the semester,
I should have time to make contributions again ... :)

Ryan