On Thu, Apr 17, 2014 at 5:00 PM, Greg Stark <st...@mit.edu> wrote: > On Thu, Apr 17, 2014 at 10:18 AM, Robert Haas <robertmh...@gmail.com> wrote: >> Because all the usage counts are the same, the eviction at >> this point is completely indiscriminate. We're just as likely to kick >> out a btree root page or a visibility map page as we are to kick out a >> random heap page, even though the former have probably been accessed >> several orders of magnitude more often. That's clearly bad. > > That's not clear at all. In that circumstance regardless of what page > you evict you're incurring precisely one page fault i/o when the page > is read back in.
I am a bit confused by this remark. In *any* circumstance when you evict you're incurring precisely one page fault I/O when the page is read back in. That doesn't mean that the choice of which page to evict is irrelevant. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
