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
