Compaq 307560-001 Performance Analysis and Capacity Planning for Microsoft Sit - Page 6

WHITE PAPER (cont.) 6... PERFORMANCE MEASUREMENTS The goal of capacity planning is to determine the types and configurations of computer systems, networks, and other resources that can support a specified number of users with a precise response time. In order to do this with realistic resources and in a reasonable amount of time, it is necessary to simulate many users interacting with the System Under Test (SUT), in this case the server being tested. The simulation tools used in this study were Microsoft's most recent versions of InetLoad and WCAT, as well as some specially developed Web pages using Microsoft ASP facilities. The most important performance measurement needed to aid in capacity planning is the maximum transaction rate for a specified load that a computer system can support. A system reaches its maximum transaction rate when its CPU or CPUs are utilized 100% of the time. This metric is called the "platform transaction capacity", and it is highly dependent on the mix of transactions used for its measurement. For example, a Web server that is tested transferring files that average 500 bytes to a simulated browser might have a platform transaction capacity of 2,000 operations per second. Another test of the same computer transferring an average file size of 7,800 bytes, which is a much more realistic average size for Web pages and graphics, would show a platform transaction capacity of 900. There are two ways to measure platform transaction capacity. The first is to simulate many people using a system with a specified sequence of transactions, including time for a person to read or think about the information returned by the system. InetLoad supports this approach. The second way to measure platform transaction capacity is to generate transactions as quickly as possible, in a random sequence, but with a specified frequency. Both InetLoad and WCAT support this approach. When measuring platform transaction capacity, it is imperative that the system's CPUs are the limiting factor, not some other aspect of the environment. This clearly requires a controlled and well defined environment. Other limitations, or bottlenecks, can greatly affect measured platform transaction capacity. Microsoft's perfmon performance monitoring tool, which comes with Windows NT Server 4.0, was used to help determine the existence and location of bottlenecks. These limitations are discussed in the "Bottlenecks" section of this document. The InetLoad Tool InetLoad supports testing multiple protocols, including the Lightweight Directory Access Protocol (LDAP), which is needed for ILS testing, and the HyperText Transfer Protocol (HTTP), which is necessary for PS testing. It works by having worker threads execute scripts on behalf of simulated users. InetLoad has a graphical user interface (GUI) that lets you set the number of users it is simulating and the number of worker threads that cycle through the script on behalf of each simulated user. Experiment with setting the number of users simulated and the number of worker threads. This will help to avoid response time artifacts based on the client system's performance In order to simulate large numbers of users, one or more copies of InetLoad must be run manually on multiple client systems. Each copy of InetLoad produces its own log file containing command response time information. To determine the response times per command type from multiple InetLoad logs, it is necessary to use Islog, another Microsoft tool, that merges and produces statistics from log files.