Added check for pg_checkpoint role presence (#807)

* Added check for pg_checkpoint role presence

This commit provides the needed infrastructure in `repmgr` so if the `repmgr` database
user is a member of the `pg_checkpoint` role, and inherits its privileges, there is no 
need for such a user to be a superuser.

Co-authored-by: Martín Marqués <martin.marques@enterprisedb.com>

dbutils.c

@@ -1852,6 +1852,51 @@ get_wal_receiver_pid(PGconn *conn)
 /* =============================== */
 
 
+/*
+ * Determine if the user associated with the current connection can execute CHECKPOINT command.
+ * User must be a supersuer or a member of the pg_checkpoint default role (available from PostgreSQL 15).
+ */
+bool
+can_execute_checkpoint(PGconn *conn)
+{
+	PQExpBufferData query;
+	PGresult   *res;
+	bool		has_pg_checkpoint_role = false;
+
+	/* superusers can do anything, no role check needed */
+	if (is_superuser_connection(conn, NULL) == true)
+		return true;
+
+	/* pg_checkpoint available from PostgreSQL 15 */
+	if (PQserverVersion(conn) < 150000)
+		return false;
+
+	initPQExpBuffer(&query);
+	appendPQExpBufferStr(&query,
+						 " SELECT pg_catalog.pg_has_role('pg_checkpoint','USAGE') ");
+
+	res = PQexec(conn, query.data);
+
+	if (PQresultStatus(res) != PGRES_TUPLES_OK)
+	{
+		log_db_error(conn, query.data,
+					 _("can_execute_checkpoint(): unable to query user roles"));
+	}
+	else
+	{
+		has_pg_checkpoint_role = atobool(PQgetvalue(res, 0, 0));
+	}
+	termPQExpBuffer(&query);
+	PQclear(res);
+
+	return has_pg_checkpoint_role;
+}
+
+
+/*
+ * Determine if the user associated with the current connection
+ * has sufficient permissions to use pg_promote function
+ */
 bool
 can_execute_pg_promote(PGconn *conn)
 {
@@ -2492,7 +2537,10 @@ get_repmgr_extension_status(PGconn *conn, t_extension_versions *extversions)
 /* node management functions */
 /* ========================= */
 
-/* assumes superuser connection */
+/*
+ * Assumes the connection can execute CHECKPOINT command.
+ * A check can be executed via 'can_execute_checkpoint' function.
+ */
 void
 checkpoint(PGconn *conn)
 {

dbutils.h

@@ -453,6 +453,7 @@ TimeLineHistoryEntry *get_timeline_history(PGconn *repl_conn, TimeLineID tli);
 pid_t		get_wal_receiver_pid(PGconn *conn);
 
 /* user/role information functions */
+bool		can_execute_checkpoint(PGconn *conn);
 bool		can_execute_pg_promote(PGconn *conn);
 bool		can_disable_walsender(PGconn *conn);
 bool		connection_has_pg_monitor_role(PGconn *conn, const char *subrole);

doc/configuration-permissions.xml

@@ -79,6 +79,10 @@
         Alternatively the meta-role <varname>pg_monitor</varname> can be granted, which includes membership
         of the above predefined roles.
       </para>
+      <para>
+        PostgreSQL 15 introduced the <varname>pg_checkpoint</varname> predefined role which allows a 
+        non-superuser &repmgr; database user to perform a CHECKPOINT command.
+      </para>
       <para>
         Membership of these roles can be granted with e.g. <command>GRANT pg_read_all_stats TO repmgr</command>.
       </para>
@@ -148,6 +152,8 @@
               <link linkend="repmgr-standby-switchover">repmgr standby switchover</link>. This can only
               be executed by a superuser; if the &repmgr; user is not a superuser,
               the <option>-S</option>/<option>--superuser</option> should be used.
+              From PostgreSQL 15 the <varname>pg_checkpoint</varname> predefined role removes the need of
+              superuser permissions to perform <command>CHECKPOINT</command> command.
             </simpara>
             <simpara>
               If &repmgr; is not able to execute <command>CHECKPOINT</command>,

doc/repmgr-node-service.xml

@@ -77,7 +77,8 @@
           </para>
           <para>
             Note that a superuser connection is required to be able to execute the
-             <command>CHECKPOINT</command> command.
+            <command>CHECKPOINT</command> command. From PostgreSQL 15 the <varname>pg_checkpoint</varname>
+            predefined role removes the need for superuser permissions to perform <command>CHECKPOINT</command> command.
           </para>
         </listitem>
      </varlistentry>

doc/repmgr-standby-switchover.xml

@@ -79,7 +79,8 @@
     <para>
       Note that <command>CHECKPOINT</command> requires database superuser permissions to execute.
       If the <literal>repmgr</literal> user is not a superuser, the name of a superuser should be
-      provided with the <option>-S</option>/<option>--superuser</option> option.
+      provided with the <option>-S</option>/<option>--superuser</option> option. From PostgreSQL 15 the <varname>pg_checkpoint</varname>
+      predefined role removes the need for superuser permissions to perform <command>CHECKPOINT</command> command.
     </para>
     <para>
       If &repmgr; is unable to execute the <command>CHECKPOINT</command> command, the switchover

repmgr-action-node.c

@@ -2365,18 +2365,25 @@ do_node_service(void)
 			conn = establish_db_connection_by_params(&source_conninfo, true);
 		}
 
-		if (is_superuser_connection(conn, NULL) == false)
+		if (can_execute_checkpoint(conn) == false)
 		{
 			if (runtime_options.dry_run == true)
 			{
-				log_warning(_("a CHECKPOINT would be issued here but no superuser connection is available"));
+				log_warning(_("a CHECKPOINT would be issued here but no authorized connection is available"));
 			}
 			else
 			{
-				log_warning(_("a superuser connection is required to issue a CHECKPOINT"));
+				log_warning(_("an authorized connection is required to issue a CHECKPOINT"));
 			}
 
-			log_hint(_("provide a superuser with -S/--superuser"));
+			if (PQserverVersion(conn) >= 150000)
+			{
+				log_hint(_("provide a superuser with -S/--superuser or grant pg_checkpoint role to repmgr user"));
+			}
+			else
+			{
+				log_hint(_("provide a superuser with -S/--superuser"));
+			}
 		}
 		else
 		{

repmgr-action-standby.c

@@ -5288,7 +5288,7 @@ do_standby_switchover(void)
 			checkpoint_conn = superuser_conn;
 		}
 
-		if (is_superuser_connection(checkpoint_conn, NULL) == true)
+		if (can_execute_checkpoint(checkpoint_conn) == true)
 		{
 			log_notice(_("issuing CHECKPOINT on node \"%s\" (ID: %i) "),
 					   config_file_options.node_name,
@@ -5297,7 +5297,16 @@ do_standby_switchover(void)
 		}
 		else
 		{
-			log_warning(_("no superuser connection available, unable to issue CHECKPOINT"));
+			log_warning(_("no authorized connection available, unable to issue CHECKPOINT"));
+
+			if (PQserverVersion(conn) >= 150000)
+			{
+				log_hint(_("provide a superuser with -S/--superuser or grant pg_checkpoint role to repmgr user"));
+			}
+			else
+			{
+				log_hint(_("provide a superuser with -S/--superuser"));
+			}
 		}
 	}