doc: add note about switchover and exclusive backups

Also rename server_not_in_exclusive_backup_mode() to avoid double
negatives.

GitHub #476.

HISTORY

@@ -18,6 +18,8 @@
           GitHub #451 (Ian)
         repmgr: fix "primary_slot_name" when using "standby clone" with --recovery-conf-only;
           GitHub #474 (Ian)
+        repmgr: don't perform a switchover if an exclusive backup is running;
+          GitHub #476 (Martín)
         repmgr: enable "witness unregister" to be run on any node; GitHub #472 (Ian)
         repmgrd: create a PID file by default; GitHub #457 (Ian)
         repmgrd: daemonize process by default; GitHub #458 (Ian)

dbutils.c

@@ -1601,6 +1601,39 @@ repmgrd_get_local_node_id(PGconn *conn)
 }
 
 
+/*
+ * Function that checks if the primary is in exclusive backup mode.
+ * We'll use this when executing an action can conflict with an exclusive
+ * backup.
+ */
+BackupState
+server_in_exclusive_backup_mode(PGconn *conn)
+{
+	BackupState backup_state = BACKUP_STATE_UNKNOWN;
+	PGresult   *res = PQexec(conn, "SELECT pg_catalog.pg_is_in_backup()");
+
+	if (PQresultStatus(res) != PGRES_TUPLES_OK)
+	{
+		log_error(_("unable to retrieve information regarding backup mode of node"));
+		log_detail("%s", PQerrorMessage(conn));
+		PQclear(res);
+		return BACKUP_STATE_UNKNOWN;
+	}
+
+	if (atobool(PQgetvalue(res, 0, 0)) == true)
+	{
+		backup_state = BACKUP_STATE_IN_BACKUP;
+	}
+	else
+	{
+		backup_state = BACKUP_STATE_NO_BACKUP;
+	}
+
+	PQclear(res);
+
+	return backup_state;
+}
+
 
 /* ================ */
 /* result functions */
@@ -3953,31 +3986,7 @@ connection_ping(PGconn *conn)
 	return;
 }
 
-/*
- * Function that checks if the primary is in exclusive backup mode.
- * We'll use this when executing an action can conflict with an exclusive
- * backup.
- */
-bool
-server_not_in_exclusive_backup_mode(PGconn *conn)
-{
-	PGresult   *res = PQexec(conn, "SELECT pg_is_in_backup()");
 
-	if (PQresultStatus(res) != PGRES_TUPLES_OK)
-	{
-		log_error(_("unable to retrieve information regarding backup mode of node"));
-		log_detail("%s", PQerrorMessage(conn));
-		PQclear(res);
-		return false;
-	}
-
-	if (strcmp(PQgetvalue(res, 0, 0), "t") == 0)
-	{
-		log_warning(_("node is in exclusive backup mode"));
-		return false;
-	}
-	return true;
-}
 
 /* ==================== */
 /* monitoring functions */

dbutils.h

@@ -96,6 +96,14 @@ typedef enum
 	SLOT_ACTIVE
 } ReplSlotStatus;
 
+typedef enum
+{
+	BACKUP_STATE_UNKNOWN = -1,
+	BACKUP_STATE_IN_BACKUP,
+	BACKUP_STATE_NO_BACKUP
+} BackupState;
+
+
 /*
  * Struct to store node information
  */
@@ -390,6 +398,7 @@ int			get_ready_archive_files(PGconn *conn, const char *data_directory);
 bool		identify_system(PGconn *repl_conn, t_system_identification *identification);
 bool		repmgrd_set_local_node_id(PGconn *conn, int local_node_id);
 int			repmgrd_get_local_node_id(PGconn *conn);
+BackupState	server_in_exclusive_backup_mode(PGconn *conn);
 
 /* extension functions */
 ExtensionStatus get_repmgr_extension_status(PGconn *conn);
@@ -467,7 +476,6 @@ int			wait_connection_availability(PGconn *conn, long long timeout);
 bool		is_server_available(const char *conninfo);
 bool		is_server_available_params(t_conninfo_param_list *param_list);
 void		connection_ping(PGconn *conn);
-bool            server_not_in_exclusive_backup_mode(PGconn *conn);
 
 /* monitoring functions  */
 void

doc/appendix-release-notes.sgml

@@ -106,6 +106,14 @@
 			</para>
 		  </listitem>
 
+          <listitem>
+            <para>
+              <command><link linkend="repmgr-standby switchover">repmgr standby switchover</link></command>
+              will refuse to run if an exclusive backup is taking place on the current primary.
+			  (GitHub #476).
+			</para>
+		  </listitem>
+
         </itemizedlist>
       </para>
     </sect2>

doc/repmgr-standby-switchover.sgml

@@ -46,6 +46,9 @@
         <application>repmgrd</application> should not be active on any nodes while a switchover is being
         executed. This restriction may be lifted in a later version.
       </para>
+      <para>
+        &repmgr; will not perform the switchover if an exclusive backup is running on the current primary.
+      </para>
     </note>
 
   </refsect1>

doc/switchover.sgml

@@ -57,7 +57,7 @@
 
    <para>
     As mentioned in the previous section, success of the switchover operation depends on
-    &repmgr;  being able to shut down the current primary server quickly and cleanly.
+    &repmgr; being able to shut down the current primary server quickly and cleanly.
    </para>
 
    <para>
@@ -121,15 +121,21 @@
     </simpara>
    </note>
 
-
    <para>
-    Check that access from applications is minimalized or preferably blocked
+     Check that access from applications is minimalized or preferably blocked
-    completely, so applications are not unexpectedly interrupted.
+     completely, so applications are not unexpectedly interrupted.
+   </para>
+
+   <note>
+     <para>
+       If an exclusive backup is running on the current primary, &repmgr; will not perform the
+       switchover.
+     </para>
    </para>
 
    <para>
-    Check there is no significant replication lag on standbys attached to the
+     Check there is no significant replication lag on standbys attached to the
-    current primary.
+     current primary.
    </para>
 
    <para>
@@ -147,6 +153,7 @@
      </para>
    </note>
 
+
    <para>
     Finally, consider executing <command>repmgr standby switchover</command> with the
     <literal>--dry-run</literal> option; this will perform any necessary checks and inform you about

repmgr-action-standby.c

@@ -2919,11 +2919,12 @@ do_standby_switchover(void)
 	 * If the DBA wants to do the switchover anyway, he should first stop the
 	 * backup that's running.
 	 */
-	if (!server_not_in_exclusive_backup_mode(remote_conn))
+	if (server_in_exclusive_backup_mode(remote_conn) != BACKUP_STATE_NO_BACKUP)
 	{
-		log_error(_("can't perform a switchover while primary server is in exclusive backup mode"));
+		log_error(_("unable to perform a switchover while primary server is in exclusive backup mode"));
 		log_hint(_("stop backup before attempting the switchover"));
 
+		PQfinish(local_conn);
 		PQfinish(remote_conn);
 
 		exit(ERR_SWITCHOVER_FAIL);