Try to use the last node in a Galera Cluster

include/MySQL_Monitor.hpp

@@ -60,6 +60,10 @@ class Galera_monitor_node {
 	Galera_monitor_node(char *_a, int _p, int _whg);
 	~Galera_monitor_node();
 	bool add_entry(unsigned long long _st, unsigned long long _ct, long long _tb, bool _pp, bool _ro, int _local_state, bool _desync, bool _reject, bool _sst_donor_reject, char *_error); // return true if status changed
+	Galera_status_entry_t *last_entry() {
+		if (idx_last_entry == -1) return NULL;
+		return (&last_entries[idx_last_entry]);
+	}
 };
 
 typedef struct _MyGR_status_entry_t {
@@ -183,6 +187,7 @@ class MySQL_Monitor {
 	void * run();
 	void populate_monitor_mysql_server_group_replication_log();
 	void populate_monitor_mysql_server_galera_log();
+	char * galera_find_last_node(int);
 };
 
 #endif /* __CLASS_MYSQL_MONITOR_H */

lib/MySQL_HostGroups_Manager.cpp

@@ -3945,6 +3945,26 @@ void MySQL_HostGroups_Manager::converge_galera_config(int _writer_hostgroup) {
 								}
 							}
 						}
+					} else {
+						if (num_writers == 0 && num_backup_writers == 0) {
+							proxy_warning("Galera: we couldn't find any healthy node for writer HG %d\n", info->writer_hostgroup);
+							// ask Monitor to get the status of the whole cluster
+							char * s0 = GloMyMon->galera_find_last_node(info->writer_hostgroup);
+							if (s0) {
+								std::string s = string(s0);
+								std::size_t found=s.find_last_of(":");
+								std::string host=s.substr(0,found);
+								std::string port=s.substr(found+1);
+								int port_n = atoi(port.c_str());
+								proxy_info("Galera: trying to use server %s:%s as a writer for HG %d\n", host.c_str(), port.c_str(), info->writer_hostgroup);
+								q=(char *)"UPDATE OR REPLACE mysql_servers_incoming SET status=0, hostgroup_id=%d WHERE hostgroup_id IN (%d, %d, %d, %d)  AND hostname='%s' AND port=%d";
+								query=(char *)malloc(strlen(q) + s.length() + 512);
+								sprintf(query,q,info->writer_hostgroup, info->writer_hostgroup, info->backup_writer_hostgroup, info->reader_hostgroup, info->offline_hostgroup, host.c_str(), port_n);
+								mydb->execute(query);
+								free(query);
+								free(s0);
+							}
+						}
 					}
 				}
 			}

lib/MySQL_Monitor.cpp

@@ -2640,3 +2640,61 @@ void MySQL_Monitor::populate_monitor_mysql_server_galera_log() {
 	}
 	pthread_mutex_unlock(&GloMyMon->galera_mutex);
 }
+
+char * MySQL_Monitor::galera_find_last_node(int writer_hostgroup) {
+/*
+	sqlite3 *mondb=monitordb->get_db();
+	int rc;
+	//char *query=NULL;
+	char *query1=NULL;
+	query1=(char *)"INSERT INTO mysql_server_galera_log VALUES (?1, ?2, ?3, ?4, ?5, ?6, ?7, ?8, ?9, ?10, ?11, ?12)";
+	sqlite3_stmt *statement1=NULL;
+*/
+	char *str = NULL;
+	pthread_mutex_lock(&GloMyMon->galera_mutex);
+/*
+	rc=sqlite3_prepare_v2(mondb, query1, -1, &statement1, 0);
+	assert(rc==SQLITE_OK);
+	monitordb->execute((char *)"DELETE FROM mysql_server_galera_log");
+*/
+	std::map<std::string, Galera_monitor_node *>::iterator it2;
+	Galera_monitor_node *node=NULL;
+	Galera_monitor_node *writer_node=NULL;
+	unsigned int writer_nodes = 0;
+	unsigned long long curtime = monotonic_time();
+	unsigned long long ti = mysql_thread___monitor_galera_healthcheck_interval;
+	ti *= 2;
+	std::string s = "";
+	for (it2=GloMyMon->Galera_Hosts_Map.begin(); it2!=GloMyMon->Galera_Hosts_Map.end(); ++it2) {
+		node=it2->second;
+		if (node->writer_hostgroup == writer_hostgroup) {
+			Galera_status_entry_t * st = node->last_entry();
+			if (st) {
+				if (st->start_time >= curtime - ti) { // only consider recent checks
+					if (st->error == NULL) { // no check error
+						if (st->read_only == false) { // the server is writable (this check is arguable)
+							if (st->wsrep_sst_donor_rejects_queries == false) {
+								if (writer_nodes == 0) {
+									s=it2->first;
+									writer_node = node;
+								}
+								writer_nodes++;
+							}
+						}
+					}
+				}
+			}
+		}
+	}
+	if (writer_node && writer_nodes == 1) {
+		// we have only one node let
+		// we don't care if status
+		str = strdup(s.c_str());
+/*
+		std::size_t found=s.find_last_of(":");
+		std::string host=s.substr(0,found);
+		std::string port=s.substr(found+1);
+*/
+	}
+	pthread_mutex_unlock(&GloMyMon->galera_mutex);
+}