master register: check for existing master presence/active record

dbutils.c

@@ -360,6 +360,83 @@ conn_to_param_list(PGconn *conn, t_conninfo_param_list *param_list)
 	}
 }
 
+
+/* ===================== */
+/* transaction functions */
+/* ===================== */
+
+bool
+begin_transaction(PGconn *conn)
+{
+	PGresult   *res;
+
+	log_verbose(LOG_DEBUG, "begin_transaction()");
+
+	res = PQexec(conn, "BEGIN");
+
+	if (PQresultStatus(res) != PGRES_COMMAND_OK)
+	{
+		log_error(_("Unable to begin transaction:\n  %s"),
+				  PQerrorMessage(conn));
+
+		PQclear(res);
+		return false;
+	}
+
+	PQclear(res);
+
+	return true;
+}
+
+
+bool
+commit_transaction(PGconn *conn)
+{
+	PGresult   *res;
+
+	log_verbose(LOG_DEBUG, "commit_transaction()");
+
+	res = PQexec(conn, "COMMIT");
+
+	if (PQresultStatus(res) != PGRES_COMMAND_OK)
+	{
+		log_error(_("Unable to commit transaction:\n  %s"),
+				  PQerrorMessage(conn));
+		PQclear(res);
+
+		return false;
+	}
+
+	PQclear(res);
+
+	return true;
+}
+
+
+bool
+rollback_transaction(PGconn *conn)
+{
+	PGresult   *res;
+
+	log_verbose(LOG_DEBUG, "rollback_transaction()");
+
+	res = PQexec(conn, "ROLLBACK");
+
+	if (PQresultStatus(res) != PGRES_COMMAND_OK)
+	{
+		log_error(_("Unable to rollback transaction:\n  %s"),
+				  PQerrorMessage(conn));
+		PQclear(res);
+
+		return false;
+	}
+
+	PQclear(res);
+
+	return true;
+}
+
+
 /* ========================== */
 /* GUC manipulation functions */
 /* ========================== */
@@ -455,7 +532,7 @@ is_standby(PGconn *conn)
 
 	if (res == NULL || PQresultStatus(res) != PGRES_TUPLES_OK)
 	{
-		log_error(_("unable to determine if server is in recovery: %s"),
+		log_error(_("unable to determine if server is in recovery:\n  %s"),
 				PQerrorMessage(conn));
 		result = -1;
 	}
@@ -467,3 +544,162 @@ is_standby(PGconn *conn)
 	PQclear(res);
 	return result;
 }
+
+/*
+ * Read the node list from the provided connection and attempt to connect to each node
+ * in turn to definitely establish if it's the cluster primary.
+ *
+ * The node list is returned in the order which makes it likely that the
+ * current primary will be returned first, reducing the number of speculative
+ * connections which need to be made to other nodes.
+ *
+ * If master_conninfo_out points to allocated memory of MAXCONNINFO in length,
+ * the primary server's conninfo string will be copied there.
+ */
+
+PGconn *
+get_master_connection(PGconn *conn,
+					  int *master_id, char *master_conninfo_out)
+{
+	PQExpBufferData	  query;
+
+	PGconn	   *remote_conn = NULL;
+	PGresult   *res;
+
+	char		remote_conninfo_stack[MAXCONNINFO];
+	char	   *remote_conninfo = &*remote_conninfo_stack;
+
+	int			i,
+				node_id;
+
+	/*
+	 * If the caller wanted to get a copy of the connection info string, sub
+	 * out the local stack pointer for the pointer passed by the caller.
+	 */
+	if (master_conninfo_out != NULL)
+		remote_conninfo = master_conninfo_out;
+
+	if (master_id != NULL)
+	{
+		*master_id = NODE_NOT_FOUND;
+	}
+
+	/* find all registered nodes  */
+	log_info(_("retrieving node list"));
+	initPQExpBuffer(&query);
+	appendPQExpBuffer(&query,
+					  "  SELECT node_id, conninfo, "
+                      "         CASE WHEN type = 'master' THEN 1 ELSE 2 END AS type_priority"
+					  "    FROM repmgr.nodes "
+					  "   WHERE type != 'witness' "
+					  "ORDER BY active DESC, type_priority, priority, node_id");
+
+	log_verbose(LOG_DEBUG, "get_master_connection():\n%s", query.data);
+
+	res = PQexec(conn, query.data);
+	if (PQresultStatus(res) != PGRES_TUPLES_OK)
+	{
+		log_error(_("unable to retrieve node records:\n  %s"),
+				  PQerrorMessage(conn));
+		PQclear(res);
+		return NULL;
+	}
+
+	termPQExpBuffer(&query);
+
+	for (i = 0; i < PQntuples(res); i++)
+	{
+		int is_node_standby;
+
+		/* initialize with the values of the current node being processed */
+		node_id = atoi(PQgetvalue(res, i, 0));
+		strncpy(remote_conninfo, PQgetvalue(res, i, 1), MAXCONNINFO);
+		log_verbose(LOG_INFO,
+					_("checking role of cluster node '%i'"),
+					node_id);
+		remote_conn = establish_db_connection(remote_conninfo, false);
+
+		if (PQstatus(remote_conn) != CONNECTION_OK)
+			continue;
+
+		is_node_standby = is_standby(remote_conn);
+
+		if (is_node_standby == -1)
+		{
+			log_error(_("unable to retrieve recovery state from node %i:\n  %s"),
+					  node_id,
+					  PQerrorMessage(remote_conn));
+			PQfinish(remote_conn);
+			continue;
+		}
+
+		/* if is_standby() returns 0, queried node is the master */
+		if (is_node_standby == 0)
+		{
+			PQclear(res);
+			log_debug(_("get_master_connection(): current master node is %i"), node_id);
+
+			if (master_id != NULL)
+			{
+				*master_id = node_id;
+			}
+
+			return remote_conn;
+		}
+
+		PQfinish(remote_conn);
+	}
+
+	PQclear(res);
+	return NULL;
+}
+
+
+
+/*
+ * Return the id of the active master node, or NODE_NOT_FOUND if no
+ * record available.
+ *
+ * This reports the value stored in the database only and
+ * does not verify whether the node is actually available
+ */
+int
+get_master_node_id(PGconn *conn)
+{
+	PQExpBufferData	  query;
+	PGresult   *res;
+	int			retval;
+
+	initPQExpBuffer(&query);
+	appendPQExpBuffer(&query,
+					  "SELECT node_id         "
+					  "  FROM repmgr.nodes    "
+					  " WHERE type = 'master' "
+					  "   AND active IS TRUE  ");
+
+	log_verbose(LOG_DEBUG, "get_master_node_id():\n%s", query.data);
+
+	res = PQexec(conn, query.data);
+
+	termPQExpBuffer(&query);
+
+	if (PQresultStatus(res) != PGRES_TUPLES_OK)
+	{
+		log_error(_("get_master_node_id(): query failed\n  %s"),
+				  PQerrorMessage(conn));
+		retval = NODE_NOT_FOUND;
+	}
+	else if (PQntuples(res) == 0)
+	{
+		log_verbose(LOG_WARNING, _("get_master_node_id(): no active primary found\n"));
+		retval = NODE_NOT_FOUND;
+	}
+	else
+	{
+		retval = atoi(PQgetvalue(res, 0, 0));
+	}
+	PQclear(res);
+
+	return retval;
+}
+

dbutils.h

@@ -119,12 +119,18 @@ PGconn *establish_db_connection_by_params(const char *keywords[],
 
 
 /* conninfo manipulation functions */
-void initialize_conninfo_params(t_conninfo_param_list *param_list, bool set_defaults);
-void copy_conninfo_params(t_conninfo_param_list *dest_list, t_conninfo_param_list *source_list);
-void conn_to_param_list(PGconn *conn, t_conninfo_param_list *param_list);
-void param_set(t_conninfo_param_list *param_list, const char *param, const char *value);
-char *param_get(t_conninfo_param_list *param_list, const char *param);
-bool parse_conninfo_string(const char *conninfo_str, t_conninfo_param_list *param_list, char *errmsg, bool ignore_application_name);
+void		initialize_conninfo_params(t_conninfo_param_list *param_list, bool set_defaults);
+void		copy_conninfo_params(t_conninfo_param_list *dest_list, t_conninfo_param_list *source_list);
+void		conn_to_param_list(PGconn *conn, t_conninfo_param_list *param_list);
+void		param_set(t_conninfo_param_list *param_list, const char *param, const char *value);
+char	   *param_get(t_conninfo_param_list *param_list, const char *param);
+bool		parse_conninfo_string(const char *conninfo_str, t_conninfo_param_list *param_list, char *errmsg, bool ignore_application_name);
+
+/* transaction functions */
+bool		begin_transaction(PGconn *conn);
+bool		commit_transaction(PGconn *conn);
+bool		rollback_transaction(PGconn *conn);
+bool		check_cluster_schema(PGconn *conn);
 
 /* GUC manipulation functions */
 bool		set_config(PGconn *conn, const char *config_param,  const char *config_value);
@@ -133,6 +139,7 @@ bool		set_config_bool(PGconn *conn, const char *config_param, bool state);
 /* Server information functions */
 int			get_server_version(PGconn *conn, char *server_version);
 int			is_standby(PGconn *conn);
-
+PGconn	   *get_master_connection(PGconn *standby_conn, int *master_id, char *master_conninfo_out);
+int			get_master_node_id(PGconn *conn);
 #endif
 

repmgr-client.c

@@ -436,8 +436,8 @@ static void
 do_master_register(void)
 {
 	PGconn	   *conn = NULL;
-
-
+	PGconn	   *master_conn = NULL;
+	int			current_master_id = UNKNOWN_NODE_ID;
 	int			ret;
 
 	log_info(_("connecting to master database..."));
@@ -468,6 +468,44 @@ do_master_register(void)
 		exit(ERR_BAD_CONFIG);
 	}
 
+	/* Ensure there isn't another active master already registered */
+	master_conn = get_master_connection(conn, &current_master_id, NULL);
+
+	if (master_conn != NULL)
+	{
+		if (current_master_id != config_file_options.node_id)
+		{
+			/* it's impossible to add a second master to a streaming replication cluster */
+			log_error(_("there is already an active registered master (node ID: %i) in this cluster"), current_master_id);
+			PQfinish(master_conn);
+			PQfinish(conn);
+			exit(ERR_BAD_CONFIG);
+		}
+
+		/* we've probably connected to ourselves */
+		PQfinish(master_conn);
+	}
+
+
+	begin_transaction(conn);
+
+	/*
+	 * Check if a node with a different ID is registered as master. This shouldn't
+	 * happen but could do if an existing master was shut down without being
+	 * unregistered.
+	*/
+
+	current_master_id = get_master_node_id(conn);
+	if (current_master_id != NODE_NOT_FOUND && current_master_id != config_file_options.node_id)
+	{
+		log_error(_("another node with id %i is already registered as master"), current_master_id);
+		// attempt to connect, add info/hint depending if active...
+		log_info(_("a streaming replication cluster can have only one master node"));
+		rollback_transaction(conn);
+		PQfinish(conn);
+		exit(ERR_BAD_CONFIG);
+	}
+
 }
 
 

strutil.h

@@ -8,6 +8,10 @@
 
 #define MAXLEN			1024
 #define MAX_QUERY_LEN	8192
+
+/* same as defined in src/include/replication/walreceiver.h */
+#define MAXCONNINFO		1024
+
 /* Why? http://stackoverflow.com/a/5459929/398670 */
 #define STR(x) CppAsString(x)