On Thu, Mar 30, 2017 at 11:17 PM, Bruce Momjian <bruce@momjian.us> wrote:
On Tue, Mar 21, 2017 at 04:04:58PM -0400, Bruce Momjian wrote: > On Tue, Mar 21, 2017 at 04:56:16PM -0300, Alvaro Herrera wrote: > > Bruce Momjian wrote: > > > On Tue, Mar 21, 2017 at 04:43:58PM -0300, Alvaro Herrera wrote: > > > > Bruce Momjian wrote: > > > > > > > > > I don't think it makes sense to try and save bits and add complexity > > > > > when we have no idea if we will ever use them, > > > > > > > > If we find ourselves in dire need of additional bits, there is a known > > > > mechanism to get back 2 bits from old-style VACUUM FULL. I assume that > > > > the reason nobody has bothered to write the code for that is that > > > > there's no *that* much interest. > > > > > > We have no way of tracking if users still have pages that used the bits > > > via pg_upgrade before they were removed. > > > > Yes, that's exactly the code that needs to be written. > > Yes, but once it is written it will take years before those bits can be > used on most installations.
Actually, the 2 bits from old-style VACUUM FULL bits could be reused if one of the WARM bits would be set when it is checked. The WARM bits will all be zero on pre-9.0. The check would have to be checking the old-style VACUUM FULL bit and checking that a WARM bit is set.