Mark, This behavior likely depends on how the data is loaded into the DBMS. If the records you are fetching are distributed widely among the 3M records on disk, then
On 1/12/07 4:31 PM, "Mark Dobbrow" <[EMAIL PROTECTED]> wrote: > Hello - > > I have a fairly large table (3 million records), and am fetching 10,000 > non-contigous records doing a simple select on an indexed column ie > > select grades from large_table where teacher_id = X > > This is a test database, so the number of records is always 10,000 and i have > 300 different teacher ids. > > The problem is, sometimes fetching un-cached records takes 0.5 secs and > sometimes (more often) is takes more like 10.0 seconds > > (fetching the same records for a given teacher_id a second time takes about > 0.25 secs) > > Has anyone seen similar behavior or know what the solution might be? > > any help much appreciated, > Mark > > > > ps. My shared_buffers is set at 5000 (kernal max), and work_mem=8192 > > >
