txid has passed the the
xmax 32 bit limit, and assuming you've not suffered any issues with wraparound because you've been correctly maintaining your tables (plenty of vacuums, vacuum freeze, etc.), what happens to the
txid? Does it just continue to increment? If so, how do
xmax store it?
It wraps around to FirstNormalTransactionId (which is 3), rather than to zero. And then it continues to increment and be stored into xmin and xmax like normal.