On Tue, Apr 26, 2011 at 4:37 PM, Kevin Grittner <Kevin.Grittner@xxxxxxxxxxxx> wrote: > Sok Ann Yap <sokann@xxxxxxxxx> 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. The very first thing to check is effective_cache_size and to set it to a reasonable value. merlin -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
