>> Probably represents freezing of old tuples, which is a WAL-logged >> operation as of 8.2. Is it likely that the data is 200M transactions >> old? >> > If nothing changed on these tables how can it freeze old tuples ? > Does it mean that once it reaches 200M transactions it will do the same > thing all over again ?
No -- once tuples are frozen, they don't need freezing again (unless they are modified by UPDATE or DELETE).
Off-topic question: the documentation says that XID numbers are 32 bit. Could the XID be 64 bit when running on a 64 bit platform? That would effectively prevent wrap-around issues.