"Greg Smith" <[EMAIL PROTECTED]> writes: > On Tue, 26 Jun 2007, Heikki Linnakangas wrote: > >> How much of the buffer cache do you think we should try to keep clean? And >> how large a percentage of the buffer cache do you think have usage_count=0 at >> any given point in time? > > What I discovered is that most of the really bad checkpoint pause cases I ran > into involved most of the buffer cache being dirty while also having a > non-zero > usage count, which left the background writer hard-pressed to work usefully > (the LRU writer couldn't do anything, and the all-scan was writing > wastefully). > I was seeing >90% dirty+usage_count>0 in the really ugly spots.
You keep describing this as ugly but it sounds like a really good situation to me. The higher that percentage the better your cache hit ratio is. If you had 80% of the buffer cache be usage_count 0 that would be about average cache hit ratio. And if you had a cache hit ratio of zero then you would find as much as little as 50% of the buffers with usage_count>0. -- Gregory Stark EnterpriseDB http://www.enterprisedb.com ---------------------------(end of broadcast)--------------------------- TIP 6: explain analyze is your friend
