> >> When the XID wraps, at the moment it does so, unless you set >> vacuum_freeze_min_age to 0 and a vacuum has just been performed, is >> there not a chance that there will be some data loss? > >No. XID comparisons are modulo 2^31. > Thanks - I'm still trying to wrap my mind around this (sorry). So, for the sake of this description: - the XID space (size 2^32) is split into two sub-spaces, each of size 2^31 - each XID is quantified in terms of "space" (0,1) plus "offset" (modulo 2^31) : x(s,o) - each db row is stamped with an "age" XID : r(s,o) - each db query start is an XID : q(s,o) Therefore, a query can only see rows where: (q.o > r.o) && (q.s == r.s) || (q.o <= r.o) && (q.s != r.s) Something like that? -- Sent via pgsql-admin mailing list (pgsql-admin@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-admin
