Re: reducing random_page_cost from 4 to 2 to force index scan

Sok Ann Yap <sokann@gmail.com> wrote:

> So, index scan wins by a very small margin over sequential scan
> after the tuning. I am a bit puzzled because index scan is more
> than 3000 times faster in this case, but the estimated costs are
> about the same. Did I do something wrong?

Tuning is generally needed to get best performance from PostgreSQL.
Needing to reduce random_page_cost is not unusual in situations
where a good portion of the active data is in cache (between
shared_buffers and the OS cache).  Please show us your overall
configuration and give a description of the hardware (how many of
what kind of cores, how much RAM, what sort of storage system).  The
configuration part can be obtained by running the query on this page
and pasting the result into your next post:

http://wiki.postgresql.org/wiki/Server_Configuration

There are probably some other configuration adjustments you could do
to ensure that good plans are chosen.

-Kevin