On Saturday 04 March 2006 08:23, hubert depesz lubaczewski wrote: > On 3/4/06, Joost Kraaijeveld <J.Kraaijeveld@xxxxxxxxxx> 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.
