Re: How to query and index for customer with lastname and city

On 3/4/06, Joost Kraaijeveld <J(dot)Kraaijeveld(at)askesis(dot)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