"Tom Lane" <[EMAIL PROTECTED]> writes: > "Umar Farooq Minhas" <[EMAIL PROTECTED]> writes: >> How can we accrately estimate the "seq_page_fetch" and = >> "random_page_fetch" costs from outside the postgres using for example a = >> C routine. > > Use a test case larger than memory. Repeat many times to average out > noise. IIRC, when I did the experiments that led to the current > random_page_cost of 4.0, it took about a week before I had numbers I > trusted.
When I was running tests I did it on a filesystem where nothing else was running. Between tests I unmounted and remounted it. As I understand it Linux associates the cache with the filesystem and not the block device and discards all pages from cache when the filesystem is unmounted. That doesn't contradict anything Tom said, it might be useful as an additional tool though. -- Gregory Stark EnterpriseDB http://www.enterprisedb.com ---------------------------(end of broadcast)--------------------------- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
