Add vacuum_truncate configuration parameter.

This new parameter works just like the storage parameter of the
same name: if set to true (which is the default), autovacuum and
VACUUM attempt to truncate any empty pages at the end of the table.
It is primarily intended to help users avoid locking issues on hot
standbys.  The setting can be overridden with the storage parameter
or VACUUM's TRUNCATE option.

Since there's presently no way to determine whether a Boolean
storage parameter is explicitly set or has just picked up the
default value, this commit also introduces an isset_offset member
to relopt_parse_elt.

Suggested-by: Will Storey <[email protected]>
Author: Nathan Bossart <[email protected]>
Co-authored-by: Gurjeet Singh <[email protected]>
Reviewed-by: Laurenz Albe <[email protected]>
Reviewed-by: Fujii Masao <[email protected]>
Reviewed-by: Robert Treat <[email protected]>
Discussion: https://postgr.es/m/Z2DE4lDX4tHqNGZt%40dev.null

1 files changed, 2 insertions, 1 deletions

diff --git a/doc/src/sgml/ref/vacuum.sgml b/doc/src/sgml/ref/vacuum.sgml
index 971b1237d47..bd5dcaf86a5 100644
--- a/doc/src/sgml/ref/vacuum.sgml
+++ b/doc/src/sgml/ref/vacuum.sgml
@@ -265,7 +265,8 @@ VACUUM [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] [ <re
       truncate off any empty pages at the end of the table and allow
       the disk space for the truncated pages to be returned to
       the operating system. This is normally the desired behavior
-      and is the default unless the <literal>vacuum_truncate</literal>
+      and is the default unless <xref linkend="guc-vacuum-truncate"/>
+      is set to false or the <literal>vacuum_truncate</literal>
       option has been set to false for the table to be vacuumed.
       Setting this option to false may be useful to avoid
       <literal>ACCESS EXCLUSIVE</literal> lock on the table that