A few paragraphs up the docs, there is this mention:
". There is a separate storage area which holds the list of members
in each multixact, which also uses a 32-bit counter and which must
also be managed."
Maybe we can add more to this paragraph, such as:
"also be managed. This member can grow to 20GB"
And then in the proposed correction:
"
Also, if the storage occupied by multixacts members area exceeds 10GB
(50% of the maximum the members area can grow), aggressive vacuum
scans will occur more often for all tables
"
What do you think?
Looks good to me, attached a v2 patch with small adjustments.
Thanks,
Alex
From 3deda711bb4219089b32204c567e735b3d7a152b Mon Sep 17 00:00:00 2001
From: Alex Friedman <alex...@gmail.com>
Date: Thu, 30 Jan 2025 17:19:07 +0200
Subject: [PATCH v2] Doc fix of aggressive vacuum threshold for multixact
members storage.
---
doc/src/sgml/maintenance.sgml | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/doc/src/sgml/maintenance.sgml b/doc/src/sgml/maintenance.sgml
index 0be90bdc7ef..f4f560bccc1 100644
--- a/doc/src/sgml/maintenance.sgml
+++ b/doc/src/sgml/maintenance.sgml
@@ -761,7 +761,8 @@ HINT: Execute a database-wide VACUUM in that database.
careful aging management, storage cleanup, and wraparound handling.
There is a separate storage area which holds the list of members in
each multixact, which also uses a 32-bit counter and which must also
- be managed.
+ be managed. This members storage area can grow up to about 20GB before
+ reaching wraparound.
</para>
<para>
@@ -792,9 +793,9 @@ HINT: Execute a database-wide VACUUM in that database.
<para>
As a safety device, an aggressive vacuum scan will
occur for any table whose multixact-age is greater than <xref
- linkend="guc-autovacuum-multixact-freeze-max-age"/>. Also, if the
- storage occupied by multixacts members exceeds 2GB, aggressive vacuum
- scans will occur more often for all tables, starting with those that
+ linkend="guc-autovacuum-multixact-freeze-max-age"/>. Also, if the
storage occupied
+ by multixacts members exceeds about 10GB (50% of the maximum the members
area can grow),
+ 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.
</para>
--
2.41.0
