Evaluation

We evaluated the performance of the VS architecture on a small Web server running on a Dell 450 MHz Intel Pentium II PC with 448 MB RAM and one UDMA HDD. The clients, three 300 MHz Pentium II machines with 128 MB RAM each, were connected through 100Mbps Ethernet. We measured the performance of Apache 1.3.6 (HTTP 1.1) on this platform running on the Linux 2.0.36 kernel. The workload was generated by the commercial SpecWeb99 benchmark [19]. SpecWeb99 attempts to model a realistic workload including 30% dynamic requests. The size of the file sets grows linearly with the number of simultaneous connections offered to the Web site. Therefore, it generally does not completely fit into the server's file cache. Dynamic requests and the use of Apache explain the low HTTP throughput of the server (ca. 220 ops/s). Since the VS abstraction is an application-transparent mechanism, neither applications nor libraries had to be modified. The management of the VS hierarchy and gate configuration was done from the command line using utilities that feed their arguments into the appropriate servctl call.