Tom, On 3/5/07 8:53 AM, "Tom Lane" <[EMAIL PROTECTED]> wrote:
> Hm, that seems to blow the "it's an L2 cache effect" theory out of the > water. If it were a cache effect then there should be a performance > cliff at the point where the cache size is exceeded. I see no such > cliff, in fact the middle part of the curve is darn near a straight > line on a log scale ... Here's that cliff you were looking for: Size of Orders table: 7178MB Blocksize: 8KB Shared_buffers Select Count Vacuum (KB) (s) (s) ======================================= 248 5.52 2.46 368 4.77 2.40 552 5.82 2.40 824 6.20 2.43 1232 5.60 3.59 1848 6.02 3.14 2768 5.53 4.56 All of these were run three times and the *lowest* time reported. Also, the behavior of "fast VACUUM after SELECT" begins abruptly at 1232KB of shared_buffers. These are Opterons with 2MB of L2 cache shared between two cores. - Luke ---------------------------(end of broadcast)--------------------------- TIP 6: explain analyze is your friend