Tuning IBM Plugin - few tips

Tuning Plugin

Modifying the WebSphere plug-in to improve performance

You can improve the performance of IBM HTTP Server (with the WebSphere Web server plug-in) by modifying the plug-in's RetryInterval configuration. The RetryInterval is the length of time to wait before trying to connect to a server that has been marked temporarily unavailable. Making this change can help the IBM HTTP Server 1.3 to scale higher than 400 users.

The plug-in marks a server temporarily unavailable if the connection to the server fails. Although a default value is 60 seconds, it is recommended that you lower this value in order to increase throughput under heavy load conditions. Lowering the RetryInterval is important for IBM HTTP Server 1.3 on UNIX operating systems that have a single thread per process, or for IBM HTTP Server 2.0 if it is configured to have fewer than 10 threads per process.

How can lowering the RetryInterval affect throughput? If the plug-in attempts to connect to a particular application server while the application server threads are busy handling other connections, which happens under heavy load conditions, the connection times out and the plug-in marks the server temporarily unavailable. If the same plug-in process has other connections open to the same server and a response is received on one of these connections, the server is marked again. However, when you use the IBM HTTP Server 1.3 on a UNIX operating system, there is no other connection since there is only one thread and one concurrent request per plug-in process. Therefore, the plug-in waits for the RetryInterval before attempting to connect to the server again.

Since the application servPublish Poster is not really down, but is busy, requests are typically completed in a small amount of time. The application server threads become available to accept more connections. A large RetryInterval causes application servers that are marked temporarily unavailable, resulting in more consistent application server CPU utilization and a higher sustained throughput.

Note: Although lowering the RetryInterval can improve performance, if all the application servers are running, a low value can have an adverse affect when one of the application servers is down. In this case, each IBM HTTP Server 1.3 process attempts to connect and fail more frequently, resulting in increased latency and decreased overall throughput.