Added 'disable_master_failback' monitor option

Added 'disable_master_failback' option in Galera monitor

server/core/config.c

@@ -38,6 +38,7 @@
  * 09/09/14	Massimiliano Pinto	Added localhost_match_wildcard_host parameter
  * 12/09/14	Mark Riddoch		Addition of checks on servers list and
  *					internal router suppression of messages
+ * 30/10/14	Massimiliano Pinto	Added disable_master_failback parameter
  *
  * @endverbatim
  */
@@ -765,6 +766,7 @@ int			error_count = 0;
 			unsigned long interval = 0;
 			int replication_heartbeat = 0;
 			int detect_stale_master = 0;
+			int disable_master_failback = 0;
 
                         module = config_get_value(obj->parameters, "module");
 			servers = config_get_value(obj->parameters, "servers");
@@ -782,6 +784,10 @@ int			error_count = 0;
 				detect_stale_master = atoi(config_get_value(obj->parameters, "detect_stale_master"));
 			}
 
+			if (config_get_value(obj->parameters, "disable_master_failback")) {
+				disable_master_failback = atoi(config_get_value(obj->parameters, "disable_master_failback"));
+			}
+
                         if (module)
 			{
 				obj->element = monitor_alloc(obj->object, module);
@@ -809,6 +815,10 @@ int			error_count = 0;
 					if(detect_stale_master == 1)
 						monitorDetectStaleMaster(obj->element, detect_stale_master);
 
+					/* disable master failback */
+					if(disable_master_failback == 1)
+						monitorDisableMasterFailback(obj->element, disable_master_failback);
+
 					/* get the servers to monitor */
 					s = strtok(servers, ",");
 					while (s)
@@ -1612,6 +1622,7 @@ static char *monitor_params[] =
 		"monitor_interval",
 		"detect_replication_lag",
 		"detect_stale_master",
+		"disable_master_failback",
                 NULL
         };
 /**

server/core/monitor.c

@@ -26,6 +26,7 @@
  * 08/07/13	Mark Riddoch		Initial implementation
  * 23/05/14	Massimiliano Pinto	Addition of monitor_interval parameter
  * 					and monitor id
+ * 30/10/14	Massimiliano Pinto	Addition of disable_master_failback parameter
  *
  * @endverbatim
  */
@@ -329,3 +330,17 @@ monitorDetectStaleMaster(MONITOR *mon, int enable)
 		mon->module->detectStaleMaster(mon->handle, enable);
 	}
 }
+
+/**
+ * Disable Master Failback
+ *
+ * @param mon		The monitor instance
+ * @param disable	The value 1 disable the failback, 0 keeps it
+ */
+void
+monitorDisableMasterFailback(MONITOR *mon, int disable)
+{
+	if (mon->module->disableMasterFailback != NULL) {
+		mon->module->disableMasterFailback(mon->handle, disable);
+	}
+}

server/include/monitor.h

@@ -33,6 +33,7 @@
  * 23/05/14	Massimiliano Pinto	Addition of defaultId and setInterval
  * 23/06/14	Massimiliano Pinto	Addition of replicationHeartbeat
  * 28/08/14	Massimiliano Pinto	Addition of detectStaleMaster
+ * 30/10/14	Massimiliano Pinto	Addition of disableMasterFailback
  *
  * @endverbatim
  */
@@ -73,6 +74,7 @@ typedef struct {
 	void	(*defaultId)(void *, unsigned long);
 	void	(*replicationHeartbeat)(void *, int);
 	void	(*detectStaleMaster)(void *, int);
+	void	(*disableMasterFailback)(void *, int);
 } MONITOR_OBJECT;
 
 /**
@@ -123,4 +125,5 @@ extern void     monitorSetId(MONITOR *, unsigned long);
 extern void     monitorSetInterval (MONITOR *, unsigned long);
 extern void     monitorSetReplicationHeartbeat(MONITOR *, int);
 extern void     monitorDetectStaleMaster(MONITOR *, int);
+extern void     monitorDisableMasterFailback(MONITOR *, int);
 #endif

server/modules/monitor/galera_mon.c

@@ -30,7 +30,7 @@
  * 					Interval is printed in diagnostics.
  * 03/06/14	Mark Riddoch		Add support for maintenance mode
  * 24/06/14	Massimiliano Pinto	Added depth level 0 for each node
- * 30/10/14	Massimiliano Pinto	Added stickininess for master selection
+ * 30/10/14	Massimiliano Pinto	Added disableMasterFailback feature
  *
  * @endverbatim
  */
@@ -53,7 +53,7 @@ extern int lm_enabled_logfiles_bitmask;
 
 static	void	monitorMain(void *);
 
-static char *version_str = "V1.2.0";
+static char *version_str = "V1.3.0";
 
 MODULE_INFO	info = {
 	MODULE_API_MONITOR,
@@ -71,6 +71,7 @@ static	void	diagnostics(DCB *, void *);
 static  void    setInterval(void *, size_t);
 static MONITOR_SERVERS *get_candidate_master(MONITOR_SERVERS *);
 static MONITOR_SERVERS *set_cluster_master(MONITOR_SERVERS *, MONITOR_SERVERS *, int);
+static	void	disableMasterFailback(void *, int);
 
 static MONITOR_OBJECT MyObject = { 
 	startMonitor, 
@@ -83,6 +84,7 @@ static MONITOR_OBJECT MyObject = {
 	NULL, 
 	NULL, 
 	NULL,
+	disableMasterFailback
 };
 
 /**
@@ -150,6 +152,7 @@ MYSQL_MONITOR *handle;
 		handle->defaultPasswd = NULL;
 		handle->id = MONITOR_DEFAULT_ID;
 		handle->interval = MONITOR_INTERVAL;
+		handle->disableMasterFailback = 0;
 		handle->master = NULL;
 		spinlock_init(&handle->lock);
 	}
@@ -438,8 +441,8 @@ monitorMain(void *arg)
 MYSQL_MONITOR		*handle = (MYSQL_MONITOR *)arg;
 MONITOR_SERVERS		*ptr;
 size_t			nrounds = 0;
-MONITOR_SERVERS		*candidate_master=NULL;
+MONITOR_SERVERS		*candidate_master = NULL;
-int		master_stickiness=1;
+int			master_stickiness = handle->disableMasterFailback;
 
 	if (mysql_thread_init())
 	{
@@ -486,7 +489,6 @@ int		master_stickiness=1;
 
 			/* clear bits for non member nodes */
 			if ( ! SERVER_IN_MAINT(ptr->server) && (ptr->server->node_id < 0 || ! SERVER_IS_JOINED(ptr->server))) {
-
 				ptr->server->depth = -1;
 
 				/* clear M/S status */
@@ -525,7 +527,6 @@ int		master_stickiness=1;
 		/* Select the master, based on master_stickiness */
 		handle->master = set_cluster_master(handle->master, candidate_master, master_stickiness);
 
-
 		ptr = handle->databases;
 
 		while (ptr && handle->master) {
@@ -573,16 +574,14 @@ MYSQL_MONITOR   *handle = (MYSQL_MONITOR *)arg;
 	memcpy(&handle->interval, &interval, sizeof(unsigned long));
 }
 
-
 /**
  * get candidate master from all nodes
  *
- * current available rule: get the server with MIN(node_id)
+ * The current available rule: get the server with MIN(node_id)
  * node_id comes from 'wsrep_local_index' variable
  *
  * @param	servers The monitored servers list
  * @return	The candidate master on success, NULL on failure
- *
  */
 static MONITOR_SERVERS *get_candidate_master(MONITOR_SERVERS *servers) {
 	MONITOR_SERVERS *ptr = servers;
@@ -618,7 +617,7 @@ static MONITOR_SERVERS *get_candidate_master(MONITOR_SERVERS *servers) {
  * The selection is based on the configuration option mapped to master_stickiness
  * The candidate master may change over time due to
  * 'wsrep_local_index' value change in the Galera Cluster
- * Enablig master_stickiness will avoid master change unless a failure is spotted
+ * Enabling master_stickiness will avoid master change unless a failure is spotted
  *
  * @param	current_master Previous master server
  * @param	candidate_master The candidate master server accordingly to the selection rule
@@ -642,3 +641,22 @@ static MONITOR_SERVERS *set_cluster_master(MONITOR_SERVERS *current_master, MONI
 			return candidate_master;
 	}
 }
+
+/**
+ * Disable/Enable the Master failback in a Galera Cluster.
+ *
+ * A restarted / rejoined node may get back the previous 'wsrep_local_index'
+ * from Cluster: if the value is the lowest in the cluster it will be selected as Master
+ * This will cause a Master change even if there is no failure.
+ * The option if set to 1 will avoid this situation, keeping the current Master (if running) available
+ *
+ * @param arg           The handle allocated by startMonitor
+ * @param disable       To disable it use 1, 0 keeps failback
+ */
+static void
+disableMasterFailback(void *arg, int disable)
+{
+MYSQL_MONITOR   *handle = (MYSQL_MONITOR *)arg;
+        memcpy(&handle->disableMasterFailback, &disable, sizeof(int));
+}
+

server/modules/monitor/mysql_mon.c

@@ -105,7 +105,8 @@ static MONITOR_OBJECT MyObject = {
 	setInterval, 
 	defaultId, 
 	replicationHeartbeat, 
-	detectStaleMaster
+	detectStaleMaster,
+	NULL
 };
 
 /**

server/modules/monitor/mysqlmon.h

@@ -65,6 +65,7 @@ typedef struct {
 	unsigned long         id;	/**< Monitor ID */
 	int	replicationHeartbeat;	/**< Monitor flag for MySQL replication heartbeat */
 	int	detectStaleMaster;	/**< Monitor flag for MySQL replication Stale Master detection */
+	int	disableMasterFailback;	/**< Monitor flag for Galera Cluster Master failback */
 	MONITOR_SERVERS *master;	/**< Master server for MySQL Master/Slave replication */
 	MONITOR_SERVERS	*databases;     /**< Linked list of servers to monitor */
 } MYSQL_MONITOR;

server/modules/monitor/ndbcluster_mon.c

@@ -73,6 +73,7 @@ static MONITOR_OBJECT MyObject = {
 	setInterval, 
 	NULL, 
 	NULL, 
+	NULL,
 	NULL
 };