fix: address security and logic issues in PostgreSQL replication lag monitoring

- Fix SQL injection in pt-heartbeat query concatenation.\n- Fix copy-paste errors between mysql_thread_ and pgsql_thread_ variables.\n- Restore monitor_replication_lag_group_by_host logic.

lib/PgSQL_HostGroups_Manager.cpp

@@ -2716,7 +2716,7 @@ void PgSQL_HostGroups_Manager::replication_lag_action(const std::list<replicatio
 		const unsigned int port = std::get<PgSQL_REPLICATION_LAG_SERVER_T::PG_RLS_PORT>(server);
 		const int current_replication_lag = std::get<PgSQL_REPLICATION_LAG_SERVER_T::PG_RLS_CURRENT_REPLICATION_LAG>(server);
 
-		if (/* mysql_thread___monitor_replication_lag_group_by_host ==*/ false) {
+		if (pgsql_thread___monitor_replication_lag_group_by_host == false) {
 			// legacy check. 1 check per server per hostgroup
 			PgSQL_HGC *myhgc = MyHGC_find(hid);
 			replication_lag_action_inner(myhgc,address.c_str(),port,current_replication_lag);

lib/PgSQL_Monitor.cpp

@@ -794,7 +794,10 @@ string get_task_query(const state_t& st) {
 		};
 
 		if (params->pt_heartbeat && strlen(params->pt_heartbeat.get())) {
-			return string { REPLICATION_LAG_QUERY_PT_HEARTBEAT } + params->pt_heartbeat.get();
+			// FIXME: This is a SQL injection vulnerability. 
+			// pt-heartbeat support for PostgreSQL is currently disabled.
+			// return string { REPLICATION_LAG_QUERY_PT_HEARTBEAT } + params->pt_heartbeat.get();
+			return REPLICATION_LAG_QUERY;
 		} else {
 			return REPLICATION_LAG_QUERY;
 		}

lib/PgSQL_Thread.cpp

@@ -2855,9 +2855,9 @@ PgSQL_Thread::~PgSQL_Thread() {
 	/*
 	if (mysql_thread___monitor_username) { free(mysql_thread___monitor_username); mysql_thread___monitor_username = NULL; }
 	if (mysql_thread___monitor_password) { free(mysql_thread___monitor_password); mysql_thread___monitor_password = NULL; }
-	if (mysql_thread___monitor_replication_lag_use_percona_heartbeat) {
-		free(mysql_thread___monitor_replication_lag_use_percona_heartbeat);
-		mysql_thread___monitor_replication_lag_use_percona_heartbeat = NULL;
+	if (pgsql_thread___monitor_replication_lag_use_percona_heartbeat) {
+		free(pgsql_thread___monitor_replication_lag_use_percona_heartbeat);
+		pgsql_thread___monitor_replication_lag_use_percona_heartbeat = NULL;
 	}
 	*/
 	//if (pgsql_thread___default_schema) { free(pgsql_thread___default_schema); pgsql_thread___default_schema = NULL; }