On 05/24/2013 07:00 PM, Robert Haas wrote: > On Fri, May 24, 2013 at 11:29 AM, Robert Haas <robertmh...@gmail.com> wrote: >> On Fri, May 24, 2013 at 10:53 AM, Andres Freund <and...@2ndquadrant.com> >> wrote: >>>> [all-visible cannot restore hint bits without FPI because of torn pages] >>> I haven't yet thought about this sufficiently yet. I think we might have >>> a chance of working around this, let me ponder a bit. >> Yeah. I too feel like there might be a solution. But I don't know >> have something specific in mind, yet anyway. > One thought I had is that it might be beneficial to freeze when a page > ceases to be all-visible, rather than when it becomes all-visible. That what I aimed to describe in my mail earlier, but your description is much clearer :) > Any operation that makes the page not-all-visible is going to emit an > FPI anyway, so we don't have to worry about torn pages in that case. > Under such a scheme, we'd have to enforce the rule that xmin and xmax > are ignored for any page that is all-visible; Agreed. We already relay on all-visible pages enough that we can trust it to be correct. Making that universal rule should not add any risks . The rule "page all-visible ==> assume all tuples frozen" would also enable VACUUM FREEZE to only work only on the non-all-visible pages . > and when a page ceases > to be all-visible, we have to go back and really freeze the > pre-existing tuples. We can do this unconditionally, or in milder case use vacuum_freeze_min_age if we want to retain xids for forensic purposes. > I think we might be able to use the existing > all_visible_cleared/new_all_visible_cleared flags to trigger this > behavior, without adding anything new to WAL at all. This seems to be easiest
-- Hannu Krosing PostgreSQL Consultant Performance, Scalability and High Availability 2ndQuadrant Nordic OÜ -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
