On 1 June 2013 21:26, Robert Haas <robertmhaas@gmail.com> wrote:
> 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.
Agreed, well done both.
What I especially like about it is how little logic it will require,
and no page format changes.
--Simon Riggs http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services