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Performance Evaluation

In this section, we present experimental results that compare the performance of the different Web server architectures presented in Section 3 on real workloads. Furthermore, we present comparative performance results for Flash and two state-of-the-art Web servers, Apache [1] and Zeus [32], on synthetic and real workloads. Finally, we present results that quantify the performance impact of the various performance optimizations included in Flash.

To enable a meaningful comparison of different architectures by eliminating variations stemming from implementation differences, the same Flash code base is used to build four servers, based on the AMPED (Flash), MT (Flash-MT), MP (Flash-MP), and SPED (Flash-SPED) architectures. These four servers represent all the architectures discussed in this paper, and they were developed by replacing Flash's event/helper dispatch mechanism with the suitable counterparts in the other architectures. In all other respects, however, they are identical to the standard, AMPED-based version of Flash and use the same techniques and optimizations.

In addition, we compare these servers with two widely-used production Web servers, Zeus v1.30 (a high-performance server using the SPED architecture), and Apache v1.3.1 (based on the MP architecture), to provide points of reference.

In our tests, the Flash-MP and Apache servers use 32 server processes and Flash-MT uses 64 threads. Zeus was configured as a single process for the experiments using synthetic workloads, and in a two-process configuration advised by Zeus for the real workload tests. Since the SPED-based Zeus can block on disk I/O, using multiple server processes can yield some performance improvements even on a uniprocessor platform, since it allows the overlapping of computation and disk I/O.

Both Flash-MT and Flash use a memory-mapped file cache with a 128 MB limit and a pathname cache limit of 6000 entries. Each Flash-MP process has a mapped file cache limit of 4 MB and a pathname cache of 200 entries. Note that the caches in an MP server have to be configured smaller, since they are replicated in each process.

The experiments were performed with the servers running on two different operating systems, Solaris 2.6 and FreeBSD 2.2.6. All tests use the same server hardware, based on a 333 MHz Pentium II CPU with 128 MB of memory and multiple 100 Mbit/s Ethernet interfaces. A switched Fast Ethernet connects the server machine to the client machines that generate the workload. Our client software is an event-driven program that simulates multiple HTTP clients [3]. Each simulated HTTP client makes HTTP requests as fast as the server can handle them.

next up previous
Next: Synthetic Workload Up: Flash: An efficient and Previous: Memory Residency Testing
Peter Druschel