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help / color / mirror / Atom feedFrom: Maxim Orlov <[email protected]>
To: Alexander Korotkov <[email protected]>
Cc: Ashutosh Bapat <[email protected]>
Cc: wenhui qiu <[email protected]>
Cc: Heikki Linnakangas <[email protected]>
Cc: Postgres hackers <[email protected]>
Subject: Re: POC: make mxidoff 64 bits
Date: Mon, 15 Sep 2025 18:42:00 +0300
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On Sat, 13 Sept 2025 at 16:34, Alexander Korotkov <[email protected]>
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.
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Subject: Re: POC: make mxidoff 64 bits
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