Memory system Behavior of Java']Java-based middleware

Java-based middleware, and application servers, in particular are rapidly, gaining importance as a new cl ass of workload for commercial multiprocessor servers. SPEC has recognized this trend with its adoption of SPECjbb2000 and the new SPECjAppServer2001 (ECperf) as standard benchmarks. Middleware, by definition, connects other tiers of server software. SPECjbb is a simple benchmark that combines middleware services, a simple database server and client drivers into a single Java program.ECperf more closely models commercial middleware by, using a commercial application server and separate machines for the different tiers. Because it is a distributed benchmark, ECperf provides an opportunity, for architects to isolate the behavior of middleware. In this paper we present a detailed characterization of the memory, system behavior of ECperf and SPECjbb using both commercial server hardware and Simics full-system simulation. We find that the memory, footprint and primary, working sets,of these workloads are small compared to other commercial workloads (e.g., on-line transaction processing), and that a large fraction of the working sets are shared between processors. We observed two key, differences between ECperf and SPECjbb that highlight the importance of isolating the behavior of the middle tier First, ECperf has a larger instruction footprint, resulting in much higher miss rates for intermediate-size instruction caches. Second, SPECjbb's data set size increases linearly,, as the benchmark scales. up, while ECperf's remains roughly constant. This difference can lead to opposite conclusions on the design of multiprocessor memory, systems, such as the utility of moderate sized (i.e., 1 MB) shared caches in a chip multiprocessor.