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From: Alvaro Herrera <[email protected]>
To: Bruce Momjian <[email protected]>
Cc: Laurenz Albe <[email protected]>
Cc: [email protected]
Cc: [email protected]
Subject: Re: 24.1.5.1. Multixacts And Wraparound
Date: Thu, 24 Jun 2021 16:06:38 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On 2021-Jun-24, Bruce Momjian wrote:

> +     As a safety device, an aggressive vacuum scan will
> +     occur for any table whose multixact-age (see <xref
> +     linkend="vacuum-for-multixact-wraparound"/>) is greater than <xref
> +     linkend="guc-autovacuum-multixact-freeze-max-age"/>.  Also, if the
> +     storage occupied by multixacts exceeds 2GB, aggressive vacuum scans
> +     will occur more often for all tables, starting with those that have
> +     the oldest multixact-age.  Both of these kinds of aggressive scans
> +     will occur even if autovacuum is nominally disabled.

This looks good, thanks.

I think "the space occupied by multixacts" is a bit ambiguous -- it is
talking about pg_multixact/members only, but you could interpret that it
talks about both that and pg_multixact/offsets.  I'm not sure we need to
be 100% precise about that, so perhaps what you have is sufficient.  But
if we do want to be precise, then maybe " ... if the storage occupied by
multixact members (<literal>pg_multixact/members/</literal>) exceeds ..."
covers it.

(At least, that's how I remember this.  I don't think things have
changed much since 53bb309d2d5a ...)

-- 
Álvaro Herrera       Valdivia, Chile

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