Monitoring and Tuning Your Server
Monitoring and Tuning Your Server |
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Each connection that an IIS 5.0 service establishes consumes some processor time. The network adapter card interrupts the processor to signal that a client has requested a connection. Further processing is required to establish and maintain the connection, to fulfill client requests sent on the connection and, when the connection is closed, processing is required to delete the structures that serviced the connection. Each time a connection is established, the load on the server increases.
One aspect of connection overhead is the time it takes to search the TCB table. TCP creates and maintains TCBs to store information about connections. This information can include, for example, data about the precedence of the connection, and its local and remote socket numbers. For efficient control, the TCBs are kept in a hash table, which is stored in the operating system’s nonpaged memory pool.
IIS 5.0 includes several features to optimize its handling of connections. Among these features are HTTP Keep-Alives, which are different from and independent of Transmission Control Protocol/Internet Protocol (TCP/IP) Keep-Alives. While the latter are messages sent to determine whether an idle connection is still active, the former maintain a connection even after the connection’s initial request is complete. The HTTP Keep-Alives feature keeps the connection active and available for subsequent requests. HTTP KeepAlives, which both the client and the server must support, are implemented to avoid the substantial cost of establishing and terminating connections. They are supported by IIS version 1.0 and later, Microsoft® Internet Explorer version 2.0 and later, and Netscape Navigator version 2.0 and later.
HTTP Keep-Alives are enabled in IIS 5.0 by default. Although they significantly improve bandwidth performance on most servers and improve the response times for clients, you can modify or eliminate them if they are not needed. You can also measure their effect on the performance of your system. To test their effect on the server, you can disable them, but it is recommended that you re-enable them when the test is concluded, to maintain the performance of the server.
Use the IIS snap-in to enable or disable HTTP Keep-Alives. You’ll find this setting on the Web Site tab of the property sheets for the Web site.
Tip When you use Microsoft Management Console (MMC), right-click to get the properties of an item in a listing.