| From: | Bertrand Drouvot <bertranddrouvot(dot)pg(at)gmail(dot)com> |
|---|---|
| To: | Sami Imseih <samimseih(at)gmail(dot)com> |
| Cc: | Alex Friedman <alexf01(at)gmail(dot)com>, pgsql-hackers(at)lists(dot)postgresql(dot)org |
| Subject: | Re: Doc fix of aggressive vacuum threshold for multixact members storage |
| Date: | 2025-02-21 09:43:43 |
| Message-ID: | Z7hKzz68VmLS8+N0@ip-10-97-1-34.eu-west-3.compute.internal |
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| Thread: | |
| Lists: | pgsql-hackers |
Hi,
On Tue, Feb 04, 2025 at 01:23:28PM -0600, Sami Imseih wrote:
> I confirmed the 20GB value as is described here [1].
> 8k page can hold 409 member groups and each
> member group can hold 4 members, thus
> (2^32/(409 *4))*8192 = 20GB.
>
Thanks for the patch!
I do agree that that's a bug in the doc.
Indeed, while I do agree that MULTIXACT_MEMBER_SAFE_THRESHOLD can be seen
as "2G" (not 2GB...) then it's compared in MultiXactMemberFreezeThreshold() to
"members" which is the number of members: So, the member's size has to be taken
into account.
Maybe we could also add a comment in multixact.c to update the doc accordingly if
the computation changes? (I think that will be easy to miss).
Regards,
--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com
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