From bb08e78972b1d0ec9f11f3d0b18903ec7a216855 Mon Sep 17 00:00:00 2001
From: David Rowley <drowley@postgresql.org>
Date: Mon, 9 Aug 2021 16:47:25 +1200
Subject: [PATCH] Doc: Fix misleading statement about VACUUM memory limits
In ec34040af I added a mention that there was no point in setting
maintenance_work_limit to anything higher than 1GB for vacuum, but that
was incorrect as ginInsertCleanup() also looks at what
maintenance_work_mem is set to during VACUUM and that's not limited to
1GB.
Here I attempt to make it more clear that the limitation is only around
the number of dead tuple identifiers that we can collect during VACUUM.
I've also added a note to autovacuum_work_mem to mention this limitation.
I didn't do that in ec34040af as I'd had some wrong-headed ideas about
just limiting the maximum value for that GUC to 1GB.
Author: David Rowley
Discussion: https://postgr.es/m/CAApHDvpGwOAvunp-E-bN_rbAs3hmxMoasm5pzkYDbf36h73s7w@mail.gmail.com
Backpatch-through: 9.6, same as ec34040af
---
doc/src/sgml/config.sgml | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 752697f07f..92ac53f9a5 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -1770,10 +1770,9 @@ include_dir 'conf.d'
setting <xref linkend="guc-autovacuum-work-mem"/>.
</para>
<para>
- Additionally, <command>VACUUM</command> is only able to utilize up to
- a maximum of <literal>1GB</literal> of memory, so
- <varname>maintenance_work_mem</varname> values higher than this have
- no effect on <command>VACUUM</command>.
+ Note that for the collection of dead tuple identifiers,
+ <command>VACUUM</command> is only able to utilize up to a maximum of
+ <literal>1GB</literal> of memory.
</para>
</listitem>
</varlistentry>
@@ -1797,6 +1796,13 @@ include_dir 'conf.d'
<filename>postgresql.conf</filename> file or on the server command
line.
</para>
+ <para>
+ For the collection of dead tuple identifiers, autovacuum is only able
+ to utilize up to a maximum of <literal>1GB</literal> of memory, so
+ setting <varname>autovacuum_work_mem</varname> to a value higher than
+ that has no effect on the number of dead tuples that autovacuum can
+ collect while scanning a table.
+ </para>
</listitem>
</varlistentry>