standby clone: warn about missing pg_rewind prerequisites

These are not essential for cloning a standby, but useful to warn
as early as possible in case the user is intending to use pg_rewind.

HISTORY

@@ -5,6 +5,8 @@
         repmgr: ensure postgresql.auto.conf is created with correct permissions (Ian)
         repmgr: minimize requirement to check upstream data directory location
           during "standby clone" (Ian)
+        repmgr: warn about missing pg_rewind prerequisites when excuting
+          "standby clone" (Ian)
         repmgr: add --upstream option to "node check"
         repmgr: report error code on follow/rejoin failure due to non-available
           replication slot (Ian)

dbutils.c

@@ -48,7 +48,7 @@ static PGconn * _establish_replication_connection_from_params(PGconn *conn, cons
 static PGconn *_get_primary_connection(PGconn *standby_conn, int *primary_id, char *primary_conninfo_out, bool quiet);
 
 static bool _set_config(PGconn *conn, const char *config_param, const char *sqlquery);
-static bool _get_pg_setting(PGconn *conn, const char *setting, char *str_output, int *int_output);
+static bool _get_pg_setting(PGconn *conn, const char *setting, char *str_output, bool *bool_output, int *int_output);
 
 static RecordStatus _get_node_record(PGconn *conn, char *sqlquery, t_node_info *node_info, bool init_defaults);
 static void _populate_node_record(PGresult *res, t_node_info *node_info, int row, bool init_defaults);
@@ -1076,7 +1076,7 @@ guc_set(PGconn *conn, const char *parameter, const char *op,
 bool
 get_pg_setting(PGconn *conn, const char *setting, char *output)
 {
-	bool success = _get_pg_setting(conn, setting, output, NULL);
+	bool success = _get_pg_setting(conn, setting, output, NULL, NULL);
 
 	if (success == true)
 	{
@@ -1086,11 +1086,24 @@ get_pg_setting(PGconn *conn, const char *setting, char *output)
 	return success;
 }
 
+bool
+get_pg_setting_bool(PGconn *conn, const char *setting, bool *output)
+{
+	bool success = _get_pg_setting(conn, setting, NULL, output, NULL);
+
+	if (success == true)
+	{
+		log_verbose(LOG_DEBUG, _("get_pg_setting(): returned value is \"%s\""),
+					*output == true ? "TRUE" : "FALSE");
+	}
+
+	return success;
+}
 
 bool
 get_pg_setting_int(PGconn *conn, const char *setting, int *output)
 {
-	bool success = _get_pg_setting(conn, setting, NULL, output);
+	bool success = _get_pg_setting(conn, setting, NULL, NULL, output);
 
 	if (success == true)
 	{
@@ -1102,7 +1115,7 @@ get_pg_setting_int(PGconn *conn, const char *setting, int *output)
 
 
 bool
-_get_pg_setting(PGconn *conn, const char *setting, char *str_output, int *int_output)
+_get_pg_setting(PGconn *conn, const char *setting, char *str_output, bool *bool_output, int *int_output)
 {
 	PQExpBufferData query;
 	PGresult   *res = NULL;
@@ -1144,9 +1157,24 @@ _get_pg_setting(PGconn *conn, const char *setting, char *str_output, int *int_ou
 		if (strcmp(PQgetvalue(res, i, 0), setting) == 0)
 		{
 			if (str_output != NULL)
+			{
 				snprintf(str_output, MAXLEN, "%s", PQgetvalue(res, i, 1));
+			}
+			else if (bool_output != NULL)
+			{
+				/*
+				 * Note we assume the caller is sure this is a boolean parameter
+				 */
+				printf("YYY %s\n", PQgetvalue(res, i, 1));
+				if (strncmp(PQgetvalue(res, i, 1), "on", MAXLEN) == 0)
+					*bool_output = true;
+				else
+					*bool_output = false;
+			}
 			else if (int_output != NULL)
+			{
 				*int_output = atoi(PQgetvalue(res, i, 1));
+			}
 
 			success = true;
 			break;

dbutils.h

@@ -429,6 +429,7 @@ bool		set_config(PGconn *conn, const char *config_param, const char *config_valu
 bool		set_config_bool(PGconn *conn, const char *config_param, bool state);
 int		    guc_set(PGconn *conn, const char *parameter, const char *op, const char *value);
 bool		get_pg_setting(PGconn *conn, const char *setting, char *output);
+bool		get_pg_setting_bool(PGconn *conn, const char *setting, bool *output);
 bool		get_pg_setting_int(PGconn *conn, const char *setting, int *output);
 bool		alter_system_int(PGconn *conn, const char *name, int value);
 bool		pg_reload_conf(PGconn *conn);

doc/appendix-release-notes.xml

@@ -49,6 +49,16 @@
       <title>General improvements</title>
       <para>
         <itemizedlist>
+
+
+          <listitem>
+            <para>
+              <link linkend="repmgr-standby-clone"><command>repmgr standby clone</command></link>:
+              Warn if neither of data page checksums or <option>wal_log_hints</option> are active,
+              as this will preclude later usage of <command>pg_rewind</command>.
+            </para>
+          </listitem>
+
           <listitem>
             <para>
               <link linkend="repmgr-standby-promote"><command>repmgr standby promote</command></link>:

repmgr-action-standby.c

@@ -6194,6 +6194,51 @@ check_upstream_config(PGconn *conn, int server_version_num, t_node_info *upstrea
 		}
 	}
 
+	/*
+	 * Finally, add some checks for recommended settings
+	 */
+
+	{
+		bool data_checksums = false;
+		bool wal_log_hints = false;
+
+		/* data_checksums available from PostgreSQL 9.3; can be read by any user */
+		if (get_pg_setting_bool(conn, "data_checksums", &data_checksums) == false)
+		{
+			/* highly unlikely this will happen */
+			log_error(_("unable to determine value for \"data_checksums\""));
+			exit(ERR_BAD_CONFIG);
+		}
+
+		/* wal_log_hints available from PostgreSQL 9.4; can be read by any user */
+		if (PQserverVersion(conn) >= 90400)
+		{
+			if (get_pg_setting_bool(conn, "wal_log_hints", &wal_log_hints) == false)
+			{
+				/* highly unlikely this will happen */
+				log_error(_("unable to determine value for \"wal_log_hints\""));
+				exit(ERR_BAD_CONFIG);
+			}
+		}
+
+		printf("XXX %i\n", PQserverVersion(conn));
+		if (data_checksums == false && wal_log_hints == false)
+		{
+			/*
+			 * If anyone's still on 9.3, there's not a lot we can do anyway
+			 */
+			if (PQserverVersion(conn) < 90400)
+			{
+				log_warning(_("data checksums are not enabled"));
+			}
+			else
+			{
+				log_warning(_("data checksums are not enabled and \"wal_log_hints\" is \"off\""));
+				log_detail(_("pg_rewind requires \"wal_log_hints\" to be enabled"));
+			}
+		}
+	}
+
 	return config_ok;
 }