On Saturday 04 March 2006 08:23, hubert depesz lubaczewski wrote:
> On 3/4/06, Joost Kraaijeveld <J.Kraaijeveld@askesis.nl> wrote:
> > > how many record do you have in the customers table?
> >
> > 368915 of which 222465 actually meet the condition.
> >
> > >From what I understand from the mailing list, PostgreSQL prefers a table
> >
> > scan whenever it expects that the number of records in the resultset
> > will be ~ > 10 % of the total number of records in the table. Which
> > explains the table scan for customers, but than again, it does not
> > explain why it uses the index on addresses: it has 369337 addresses of
> > which 158003 meet the condition
>
> bitmap index scan is faster than sequential table scan. that's all. it
> was introduced in 8.1 as far as i remember.
> basically - i doubt if you can get better performace from query when
> the result row-count is that high.
>
> out of curiosity though - why do you need so many rows? it's not
> possible to view them, nor do anything meaningful with 200 thousand
> rows!
>
> depesz
If you're just displaying, use limit and offset to grab one page at a time.
If you're manipulating it would be a good idea to do something in a stored
procedure.