On Jan 5, 2011, at 8:10 PM, Robert Haas wrote: > On Wed, Jan 5, 2011 at 3:22 PM, Jesper Krogh <jes...@krogh.cc> wrote: >> Given a crash-safe visibility map, what purpuse does the PD_ALL_VISIBLE bit >> serve? > > If we modify a page on which PD_ALL_VISIBLE isn't set, we don't > attempt to update the visibility map. In theory, this is an important > optimization to reduce contention on the visibility map page, since > there are something like 64K heap pages per visibility map page. In > practice, I'm not sure in what workloads it matters or by how much.
What specific locking are you worried about? The page locks themselves? Isn't changing the bit essentially a single instruction operation? This is sounding like premature optimization... ;) -- Jim C. Nasby, Database Architect j...@nasby.net 512.569.9461 (cell) http://jim.nasby.net -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
