Venkat Balaji <venkat.balaji@xxxxxxxx> wrote: > The cost is "13.88" to fetch 1 row by scanning an Primary Key > indexed column. > > Isn't the cost for fetching 1 row is too high ? I don't know, how many index pages will need to be randomly accessed in addition to the random heap access? How many dead versions of the row will need to be visited besides the row which is actually visible? How many of these pages are in shared_buffers? How many of these pages are in OS cache? > I am looking for a way to reduce cost as much as possible because > the query executes 100000+ times a day. Well, you can reduce the cost all you want by dividing all of the costing factors in postgresql.conf by the same value, but that won't affect query run time. That depends on the query plan which is chosen. The cost is just an abstract number used for comparing the apparent resources needed to run a query through each of the available plans. What matters is that the cost factors accurately reflect the resources used; if not you should adjust them. If you calculate a ratio between run time and estimated cost, you should find that it remains relatively constant (like within an order of magnitude) for various queries. Since you didn't show actual run times, we can't tell whether anything need adjustment. -Kevin -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
