Open vSwitch (OVS) is a widely used virtual switch designed to provide virtual network capabilities in virtualized environments. As the core of OVS, the packet classification task is time-consuming with the implementation of Tuple Space Search (TSS), a classical hash table-based algorithm that can achieve fast rule updating but at the cost of the reduced packet classification throughput. However, because of the central role of OVS in a virtualized environment, its performance is of utmost importance and we need mechanisms that can achieve high update rate along with high packet classification throughput. In this paper, we compare the performance of several classification algorithms and show that Tuple Merge Relaxation (TMR) is able to achieve the highest sustainable classification throughput while dealing with updates. After integrating it into OVS and evaluating its in vivo performance, we observe that TMR-OVS can achieve up to $24.7\times$ higher throughput compared with native OVS. Moreover, we show that TMR-OVS is also effective against Tuple Space Explosion attack effectively and maintains OVS throughput under this attack.