Added duplicate server check to prevent redundant server inspections,…

… that can cause unique constraint error on mysql_server_galera_log table.

lib/MySQL_Monitor.cpp

@@ -8014,14 +8014,19 @@ bool MySQL_Monitor::monitor_galera_process_ready_tasks(const std::vector<MySQL_M
 void MySQL_Monitor::monitor_galera_async() {
 
 	std::vector<std::unique_ptr<MySQL_Monitor_State_Data>> mmsds;
-
+	std::set<std::string> checked_servers;
 	pthread_mutex_lock(&galera_mutex);
 	assert(Galera_Hosts_resultset);
 	mmsds.reserve(Galera_Hosts_resultset->rows_count);
 	Monitor_Poll monitor_poll(Galera_Hosts_resultset->rows_count);
 
 	for (std::vector<SQLite3_row*>::iterator it = Galera_Hosts_resultset->rows.begin(); it != Galera_Hosts_resultset->rows.end(); ++it) {
 		const SQLite3_row* r = *it;
+
+		auto ret = checked_servers.insert(std::string(r->fields[1]) + ":" + std::string(r->fields[2]));
+		if (ret.second == false) // duplicate server entry
+			continue;
+
 		bool rc_ping = server_responds_to_ping(r->fields[1], atoi(r->fields[2]));
 		if (rc_ping) { // only if server is responding to pings