Re: Add 64-bit XIDs into PostgreSQL 15

Hi!

Here is a rebased and improved version of the patchset: now we use 64 bit atomic operations on shared memory which was not previously warrantied on 32 bit architectures.

Before this change under heavy transaction concurrency we've got a warning "xmin is far in the past", rarely. This was seen on 32 bit architectures.

On 64 bit these changes do not change performance since 64 bit atomicity is automatically fulfilled.