Re: POC: make mxidoff 64 bits
От | wenhui qiu |
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Тема | Re: POC: make mxidoff 64 bits |
Дата | |
Msg-id | CAGjGUAJUmSFMunCcK8DXcjLrs2Hfk2kFiaWDTc6ti03S8Echmw@mail.gmail.com обсуждение исходный текст |
Ответ на | Re: POC: make mxidoff 64 bits (Maxim Orlov <orlovmg@gmail.com>) |
Ответы |
Re: POC: make mxidoff 64 bits
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Список | pgsql-hackers |
Hi Maxim
Thanks
Thanks for your continued efforts to get XID64 implemented.
> 32kB page may contain then 2^13-2 offsets, each is maxed by 2^18+1.
> 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.
Agree +1 , but I have a question: I remember the XID64 patch got split into a few threads. How are these threads related? The original one was seen as too big a change, so it was broken up after people raised concerns.
Agree +1 , but I have a question: I remember the XID64 patch got split into a few threads. How are these threads related? The original one was seen as too big a change, so it was broken up after people raised concerns.
On Mon, Sep 15, 2025 at 11:42 PM Maxim Orlov <orlovmg@gmail.com> wrote:
On Sat, 13 Sept 2025 at 16:34, Alexander Korotkov <aekorotkov@gmail.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 a8 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 alwaysfit uint32.It appears logical to me.
--Best regards,Maxim Orlov.
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