autovacuum_disable_relation_truncation.v2.patch

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index e55700f35b8..17d94d7ce58 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -8934,6 +8934,42 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-autovacuum-vacuum-truncate" xreflabel="autovacuum_vacuum_truncate">
+       <term><varname>autovacuum_vacuum_truncate</varname> (<type>boolean</type>)
+       <indexterm>
+        <primary><varname>autovacuum_vacuum_truncate</varname></primary>
+        <secondary>configuration parameter</secondary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Enables or disables autovacuum to try to truncate off any empty pages
+         at the end of the tables, as it processes them. The default value is
+         <literal>true</literal>.
+
+         If <literal>true</literal>, autovacuum will perforn the truncation and
+         the disk space for the truncated pages is returned to the operating
+         system.
+
+         This is normally the desired behavior and is the default unless the
+         <literal>vacuum_truncate</literal> option for a table being vacuumed
+         has been set to <literal>false</literal>.
+
+         If <literal>false</literal>, autovacuum will not perform the truncation
+         on any tables it vacuums. The <literal>vacuum_truncate</literal> option
+         on the tables is ignored.
+
+         Note that the truncation requires <literal>ACCESS EXCLUSIVE</literal>
+         lock on the table.
+
+         Setting this option to <literal>false</literal> may be useful to avoid
+         <literal>ACCESS EXCLUSIVE</literal> lock on the table that the
+         truncation requires.
+
+        </para>
+       </listitem>
+      </varlistentry>
+
      </variablelist>
     </sect2>
 
diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index ddb303f5201..d8261a9b19d 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -115,6 +115,7 @@
  * GUC parameters
  */
 bool		autovacuum_start_daemon = false;
+bool		autovacuum_vacuum_truncate = true;
 int			autovacuum_worker_slots;
 int			autovacuum_max_workers;
 int			autovacuum_work_mem = -1;
@@ -2812,12 +2813,16 @@ table_recheck_autovac(Oid relid, HTAB *table_toast_map,
 			(!wraparound ? VACOPT_SKIP_LOCKED : 0);
 
 		/*
-		 * index_cleanup and truncate are unspecified at first in autovacuum.
-		 * They will be filled in with usable values using their reloptions
-		 * (or reloption defaults) later.
+		 * index_cleanup is unspecified at first in autovacuum. truncate is
+		 * unspecified, unless it is disabled via the GUC parameter.
+		 *
+		 * The unspecified options will be filled in with usable values using
+		 * their reloptions (or reloption defaults) later.
 		 */
 		tab->at_params.index_cleanup = VACOPTVALUE_UNSPECIFIED;
-		tab->at_params.truncate = VACOPTVALUE_UNSPECIFIED;
+		tab->at_params.truncate = (autovacuum_vacuum_truncate == false)
+									? VACOPTVALUE_DISABLED
+									: VACOPTVALUE_UNSPECIFIED;
 		/* As of now, we don't support parallel vacuum for autovacuum */
 		tab->at_params.nworkers = -1;
 		tab->at_params.freeze_min_age = freeze_min_age;
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index ad25cbb39c5..d1443256110 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -1531,6 +1531,16 @@ struct config_bool ConfigureNamesBool[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"autovacuum_vacuum_truncate", PGC_SIGHUP, VACUUM_AUTOVACUUM,
+			gettext_noop("Disables autovacuum behavior of truncatiing relations."),
+			NULL
+		},
+		&autovacuum_vacuum_truncate,
+		true,
+		NULL, NULL, NULL
+	},
+
 	{
 		{"trace_notify", PGC_USERSET, DEVELOPER_OPTIONS,
 			gettext_noop("Generates debugging output for LISTEN and NOTIFY."),
diff --git a/src/include/postmaster/autovacuum.h b/src/include/postmaster/autovacuum.h
index 6a95e5f55bd..d0bd6f498c7 100644
--- a/src/include/postmaster/autovacuum.h
+++ b/src/include/postmaster/autovacuum.h
@@ -28,6 +28,7 @@ typedef enum
 
 /* GUC variables */
 extern PGDLLIMPORT bool autovacuum_start_daemon;
+extern PGDLLIMPORT bool autovacuum_vacuum_truncate;
 extern PGDLLIMPORT int autovacuum_worker_slots;
 extern PGDLLIMPORT int autovacuum_max_workers;
 extern PGDLLIMPORT int autovacuum_work_mem;