On Thu, Apr 17, 2014 at 9:21 AM, Stephen Frost <sfr...@snowman.net> wrote: > * Robert Haas (robertmh...@gmail.com) wrote: >> several orders of magnitude more often. That's clearly bad. On >> systems that are not too heavily loaded it doesn't matter too much >> because we just fault the page right back in from the OS pagecache. > > Ehhh. No. If it's a hot page that we've been holding in *our* cache > long enough, the kernel will happily evict it as 'cold' from *its* > cache, leading to... > >> But I've done pgbench runs where such decisions lead to long stalls, >> because the page has to be brought back in from disk, and there's a >> long I/O queue; or maybe just because the kernel thinks PostgreSQL is >> issuing too many I/O requests and makes some of them wait to cool >> things down. > > Exactly this.
Yes, I believe that's why this is so effective. -- Peter Geoghegan -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
