On Tue, Jun 2, 2015 at 5:22 PM, Andres Freund <andres@xxxxxxxxxxx> wrote: >> > Hm. If GetOldestMultiXactOnDisk() gets the starting point by scanning >> > the disk it'll always get one at a segment boundary, right? I'm not sure >> > that's actually ok; because the value at the beginning of the segment >> > can very well end up being a 0, as MaybeExtendOffsetSlru() will have >> > filled the page with zeros. >> > >> > I think that should be harmless, the worst that can happen is that >> > oldestOffset errorneously is 0, which should be correct, even though >> > possibly overly conservative, in these cases. >> >> Uh oh. That seems like a real bad problem for this approach. What >> keeps that from being the opposite of too conservative? There's no >> "safe" value in a circular numbering space. > > I think it *might* (I'm really jetlagged) be fine because that'll only > happen after a upgrade from < 9.3. And in that case we initialize > nextOffset to 0. That ought to safe us? That's pretty much betting the farm on the bugs we know about today being the only ones there are. That seems imprudent. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
