Re: Add 64-bit XIDs into PostgreSQL 15

On Thu, Dec 30, 2021 at 03:15:16PM +0300, Maxim Orlov wrote:
> PFA updated working patch v6 for PG15 development cycle.
> It is based on a patch by Alexander Korotkov version 5 [5] with a few fixes,
> refactoring and was rebased to PG15.
>
> Main changes:
> - Change TransactionId to 64bit
> - Disk tuple format (HeapTupleHeader) is unchanged: xmin and xmax
>   remains 32bit
> -- 32bit xid is named ShortTransactionId now.
> -- Exception: see "double xmax" format below.
> - Heap page format is changed to contain xid and multixact base value,
>   tuple's xmin and xmax are offsets from.
> -- xid_base and multi_base are stored as a page special data. PageHeader
>    remains unmodified.
> -- If after upgrade page has no free space for special data, tuples are
>    converted to "double xmax" format: xmin became virtual
>    FrozenTransactionId, xmax occupies the whole 64bit.
>    Page converted to new format when vacuum frees enough space.

I think it is a great idea to allow the 64-XID to span the 32-bit xmin
and xmax fields when needed. It would be nice if we can get focus on
this feature so we are sure it gets into PG 15. Can we add this patch
incrementally so people can more easily analyze it?

--
Bruce Momjian <bruce(at)momjian(dot)us> https://momjian.us
EDB https://enterprisedb.com

If only the physical world exists, free will is an illusion.