Spare Instance: an Adaptive Mechanism for Managing Cluster Applications

Some measurements of performance have been conducted in Dawning 4000 cluster. We measured the elapsed time of putting the spare instance into use to be 0.12 sec by redirection, while taking the old policy, the time for an Apache instance takes 1.05 sec. For an Oracle 10G, the cost is 7.69 sec. The spare servers contribute to a public spare resource pool. In the case of the master instance´s failure, the spare instance avoids service gap and provide non-stop service. For the SLA violation incurred by the short time overload, the available resource could be enlarged instantaneously, much quickly than launching a new instance temporarily. In the best case, the service capacity may be enhanced one time, thus the QoS performance could be guaranteed. Furthermore, for the workload fluctuation, the overhead of frequently launching and terminating instance has been cut down. By introducing the spare instance, the adaptive capacity of the application has been greatly improved in the case of short-term overload and the workload fluctuation