I want to once again open the topic of 64 bit transaction id. I did not manage to find in the archive of the option that I want to discuss, so I write. If I searched poorly, then please forgive me.
The idea is not very original and probably has already been considered, again I repeat - I did not find it. Therefore, please do not scold me severely.
In discussions of 64-bit transaction id, I did not find mention of an algorithm for storing them, as it was done, for example, in MS SQL Server.
What if instead of 2 fields (xmin and xmax) with a total length of 64 bits - use 1 field (let's call it xid) with a length of 64 bits in tuple header? In this field store the xid of the transaction that created the version. In this case, the new transaction in order to understand whether the read version is suitable for it or not, will have to read the next version as well. Those. The downside of such decision is of course an increase in I / O. Transactions will have to read the +1 version. On the plus side, the title of the tuple remains the same length.
is 32 bit tid really problem? Why you need to know state of last 2^31 transactions? Is not problem in too low usage (or maybe too high overhead) of VACUUM FREEZE.
I am not sure if increasing this range can has much more fatal problems (maybe later)
