On 07/03/2023 13:38, Maxim Orlov wrote:
As for making pg_multixact 64 bit, I spend the last couple of days to make proper pg_upgrade for pg_multixact's and for pg_xact's with wraparound and I've understood, that it is not a simple task compare to pg_xact's. The problem is, we do not have epoch for multixacts, so we do not have ability to "overcome" wraparound. The solution may be adding some kind of epoch for multixacts or make them 64 bit in "main" 64-xid patch, but in perspective of this thread, in my view, this should be last in line here.
That is true for pg_multixact/offsets. We will indeed need to add an epoch and introduce the concept of FullMultiXactIds for that. However, we can change pg_multixact/members independently of that. We can extend MultiXactOffset from 32 to 64 bits, and eliminate pg_multixact/members wraparound, while keeping multi-xids 32 bits wide.
- Heikki
