Alvaro Herrera wrote: > > That would probably work, but the existing coding actually makes more > > sense. It's essentially trying to scan backwards by > > autovacuum_freeze_max_age XIDs through the circular XID space. But > > the XID space isn't actually circular, because there are 3 special > > values. So if we land on one of those values we want to skip backward > > by 3. Here FirstNormalTransactionId doesn't represent itself, but > > rather the number of special XIDs that exist. > > Yeah, I think this change would have the effect of moving the freeze > limit by one (or two?) counts. Given the moving nature of values > returned by ReadNewTransactionId this would probably have no practical > effect. Still, the code as is seems more natural to me (Tom wrote this > bit IIRC, not me).
I am now thinking the code is correct --- it maps values from 0 to FirstNormalTransactionId into the top of the (unsigned) xid range. Unless someone objects, I will add a C comment about this behavior so future readers are not confused. -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
