On Fri, Nov 20, 2020 at 9:08 AM Alvaro Herrera <alvhe...@alvh.no-ip.org> wrote: > There are two costs associated with this processing. One is dirtying > the page (which means it needs to be written down when evicted), and the > other is to write WAL records for each change. The cost for the latter > is going to be the same in both cases (with this change and without) > because the same WAL will have to be written -- the only difference is > *when* do you pay it. The cost of the former is quite different; with > Simon's patch we dirty the page once, and without the patch we may dirty > it several times before it becomes "stable" and no more writes are done > to it. > > (If you have tables whose pages change all the time, there would be no > difference with or without the patch.) > > Dirtying the page less times means less full-page images to WAL, too, > which can be significant.
Yeah, I think dirtying the page fewer times is a big win. However, a page may have tuples that are not yet all-visible, and we can't freeze those just because we are freezing others. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company
