Simplified and improved logic for connection cleanup and creation when a matching connection isn't found

lib/MySQL_HostGroups_Manager.cpp

@@ -3132,34 +3132,29 @@ MySQL_Connection * MySrvConnList::get_random_MyConn(MySQL_Session *sess, bool ff
 						unsigned int pct_max_connections = (3 * mysrvc->max_connections) / 4;
 						unsigned int connections_to_free = 0;
 
-						if (pct_max_connections <= (conns_free + conns_used)) {
-							connections_to_free = (conns_free + conns_used) - pct_max_connections;
-							connections_to_free = connections_to_free == 0 ? 1 : connections_to_free;
-						}
+						if (conns_free >= 1) {
+							// connection cleanup is triggered when connectinos exceed 3/4 of the total
+							// allowed max connections, this cleanup ensures that at least *one connection*
+							// will be freed.
+							if (pct_max_connections <= (conns_free + conns_used)) {
+								connections_to_free = (conns_free + conns_used) - pct_max_connections;
+								if (connections_to_free == 0) connections_to_free = 1;
+							}
 
-						while (conns_free && connections_to_free) {
-							MySQL_Connection* conn = mysrvc->ConnectionsFree->remove(0);
-							delete conn;
+							while (conns_free && connections_to_free) {
+								MySQL_Connection* conn = mysrvc->ConnectionsFree->remove(0);
+								delete conn;
 
-							conns_free = mysrvc->ConnectionsFree->conns_length();
-							connections_to_free -= 1;
+								conns_free = mysrvc->ConnectionsFree->conns_length();
+								connections_to_free -= 1;
+							}
 						}
 
-						conns_used = mysrvc->ConnectionsUsed->conns_length();
-
-						if (mysrvc->max_connections > (conns_used + conns_free)) {
-							// we must create a new connection
-							conn = new MySQL_Connection();
-							conn->parent=mysrvc;
-							__sync_fetch_and_add(&MyHGM->status.server_connections_created, 1);
-							proxy_debug(PROXY_DEBUG_MYSQL_CONNPOOL, 7, "Returning MySQL Connection %p, server %s:%d\n", conn, conn->parent->address, conn->parent->port);
-						} else {
-							// no suitable connection was found, and the number of
-							// used connections already reached 'max_connections'
-							proxy_debug(PROXY_DEBUG_MYSQL_CONNPOOL, 7, "No suitable connection found, 'max_connections' reached for server %s:%d\n", conn->parent->address, conn->parent->port);
-							__sync_fetch_and_add(&MyHGM->status.server_connections_delayed, 1);
-							return NULL;
-						}
+						// we must create a new connection
+						conn = new MySQL_Connection();
+						conn->parent=mysrvc;
+						__sync_fetch_and_add(&MyHGM->status.server_connections_created, 1);
+						proxy_debug(PROXY_DEBUG_MYSQL_CONNPOOL, 7, "Returning MySQL Connection %p, server %s:%d\n", conn, conn->parent->address, conn->parent->port);
 					}
 					break;
 				case 1: //tracked options are OK , but CHANGE USER is required