On Mon, Jun 29, 2015 at 1:54 AM, Jeff Janes <jeff.ja...@gmail.com> wrote: > Attached is a patch that implements the vm scan for truncation. It > introduces a variable to hold the last blkno which was skipped during the > forward portion. Any blocks after both this blkno and after the last > inspected nonempty page (which the code is already tracking) must have been > observed to be empty by the current vacuum. Any other process rendering the > page nonempty are required to clear the vm bit, and no other process can set > the bit again during the vacuum's lifetime. So if the bit is still set, the > page is still empty without needing to inspect it.
Urgh. So if we do this, that forever precludes having HOT pruning set the all-visible bit. At the least we'd better document that carefully so that nobody breaks it later. But I wonder if there isn't some better approach, because I would certainly rather that we didn't foreclose the possibility of doing something like that in the future. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
