Re: POC: make mxidoff 64 bits

On Sat, 13 Sept 2025 at 16:34, Alexander Korotkov <aekorotkov(at)gmail(dot)com>
wrote:

>
> Therefore, we can change from each 8 of 32-bit multixact offsets
> (takes 32-bytes) to one 64-bit offset + 7 of 24-bit offset increments
> (takes 29-bytes). The actual multixact offsets can be calculated at
> the fly, overhead shouldn't be significant. What do you think?
>
>
Thank you for your review; I'm pleased to hear from you again.

Yes, because the maximum number of mxoff is limited by the number of
running transactions, we may do it that way.
However, it is a bit wired to have offsets with the 7-byte "base".

I believe we may take advantage of the 64XID patch's notion of putting a
8 byte base followed by 4 byte offsets for particular page.

32kB page may contain then 2^13-2 offsets, each is maxed by 2^18+1.
Therefore, offset from base will never overflow 2^31 and will always
fit uint32.

It appears logical to me.

--
Best regards,
Maxim Orlov.