On Sat, Jun 1, 2013 at 3:22 PM, Simon Riggs <simon@2ndquadrant.com> wrote:
> If we set a bit, surely we need to write the page. Isn't that what we
> were trying to avoid?
No, the bit only gets set in situations when we were going to dirty
the page for some other reason anyway. Specifically, if a page
modification discovers that we've switched epochs (but just once) and
the bit isn't already set, we can set it in lieu of scanning the
entire page for tuples that need freezing.
Under this proposal, pages that don't contain any dead tuples needn't
be dirtied for freezing, ever. Smells like awesome.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company