On Thu, Feb 23, 2017 at 03:58:59PM -0300, Alvaro Herrera wrote: > Bruce Momjian wrote: > > On Thu, Feb 23, 2017 at 03:45:24PM -0300, Alvaro Herrera wrote: > > > > > and potentially trim the first HOT chain as those tuples become > > > > invisible. > > > > > > That can already happen even without WARM, no? > > > > Uh, the point is that with WARM those four early tuples can be removed > > via a prune, rather than requiring a VACUUM. Without WARM, the fourth > > tuple can't be removed until the index is cleared by VACUUM. > > I *think* that the WARM-updated one cannot be pruned either, because > it's pointed to by at least one index (otherwise it'd have been a HOT > update). The ones prior to that can be removed either way.
Well, if you can't prune across index-column changes, how is a WARM update different than just two HOT chains with no WARM linkage? > I think the part you want (be able to prune the WARM updated tuple) is > part of what Pavan calls "turning the WARM chain into a HOT chain", so > not part of the initial patch. Pavan can explain this part better, and > also set me straight in case I'm wrong in the above :-) VACUUM can already remove entire HOT chains that have expired. What his VACUUM patch does, I think, is to remove the index entries that no longer point to values in the HOT/WARM chain, turning the chain into fully HOT, so another WARM addition to the chain can happen. -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + As you are, so once was I. As I am, so you will be. + + Ancient Roman grave inscription + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
