The proposed option is not much different from what it is now.

We are not trying to save some space - we will reuse the existing one. We just work in 64 bit transaction counters. Correct me if I'm wrong - the address of the next version of the line is stored in the 6 byte field t_cid in the tuple header - which is not attached to the current page in any way - and can be stored anywhere in the table. Nothing changes.

I often explain things very poorly, but I will try.

for example

Each transaction is assigned a unique 64-bit xid.

In the tuple header, we replace 32-bit xmin and xmax - with one 64-bit field - let's call it xid.

Suppose

Transaction 1 does INSERT

The first version is created (Tuple1).

Tuple1. Tuple_header.xid = Transacrion1.xid and Tuple1. Tuple_header. t_cid = 0;

Transaction 3 (started after transaction 1) does UPDATE

The second version is created (Tuple2).

Tuple1. Tuple_header. t_cid = (address) Tuple2;

Tuple2. Tuple_header.xid = Transacrion3.xid and Tuple2. Tuple_header. t_cid = 0;

Transaction 2 (started between transaction1 and transaction2) makes SELECT

Reads Tuple1. Transaction 2 sees that Tuple1.Tuple_header.xid <Transacrion2.xid, sees that the address Tuple1 is filled. Tuple_header. t_cid, follow it and read the version of Tuple2.