On Friday January 30 2004 6:06, Martijn van Oosterhout wrote: > On Fri, Jan 30, 2004 at 03:19:56PM -0700, Ed L. wrote: > > > > I'm also curious about the relationship of DB shared buffer cache to > > the linux/hpux kernel caches. ... > > Whenever the database needs a block not in memory it get loaded and ends > up in both the OS cache and the DB cache. The difference between getting > a block out of DB cache and OS cache is very, very small compared to > loading off disk.
So the OS cache and the DB cache may well have duplicate copies of the data? With OS cache being more susceptible to preemption from other processes? > Finally, at least on Linux, the shared memory postgres uses for cache can > also be swapped out making it very difficult to determine the correct > value. What would cause DB shared memory to be swapped out in linux? I thought it was all pre-allocated at pgsql startup. Is this the "well its not really pre-allocated but rather supplied on demand" story? I think I saw some sort of kernel parameter controlling a similar (same?) policy... TIA. ---------------------------(end of broadcast)--------------------------- TIP 4: Don't 'kill -9' the postmaster
