On 3/10/2010 7:39 AM, Richard Troy wrote:
I can't speak for modern "OpenVMS", but "back in the day", VMS had a very effective memory management strategy which, in effect, made it as if all memory was a cache for disk. It did this by means of a mechanism by which to identify all potentially reachable disk space. When disk was read in, an entry would be made mapping the memory to the disk space from which it came - and if it was later updated, the mapping entry was marked "dirty." Whenever disk access was contemplated, a check was made to see if it was already in memory and if so, it'd provide access to the in-memory copy instead of doing the read again. (This also permitted, under some circumstances, to reduce write activity as well.)
That's how Linux's memory management works, too, at least if I understand you correctly. Pretty much every modern OS does it. Pg is reliant on the operating system's disk cache, and has some minimal knowledge of it (see effective_cache_size) .
I don't know how shared_buffers management works, but certainly at the OS cache level that's what already happens.
-- Craig Ringer Tech-related writing at http://soapyfrogs.blogspot.com/ -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
