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Sun Java System Web Server 6.1 SP6 Performance Tuning, Sizing, and Scaling Guide

Process Modes

You can run Sun Java System Web Server in one of the following two modes:

Single-Process Mode

In the single-process mode the server receives requests from web clients to a single process. Inside the single server process many threads are running that are waiting for new requests to arrive. When a request arrives, it is handled by the thread receiving the request. Because the server is multi-threaded, all NSAPI extensions written to the server must be thread-safe. This means that if the NSAPI extension uses a global resource, like a shared reference to a file or global variable, then the use of that resource must be synchronized, so that only one thread accesses it at a time. All plugins provided by Netscape/Sun Java System are thread-safe and thread-aware, providing good scalability and concurrency. However, your legacy applications may be single-threaded. When the server runs the application, it can only execute one at a time. This leads to server performance problems when put under load. Unfortunately, in the single-process design, there is no real workaround.

Multi-Process Mode

You can configure the server to handle requests using multiple processes with multiple threads in each process. This flexibility provides optimal performance for sites using threads, and also provides backward compatibility to sites running legacy applications that are not ready to run in a threaded environment. Because applications on Windows generally already take advantage of multi-thread considerations, this feature applies to UNIX/Linux platforms.

The advantage of multiple processes is that legacy applications that are not thread-aware or thread-safe can be run more effectively in Sun Java System Web Server. However, because all of the Netscape/Sun ONE extensions are built to support a single-process threaded environment, they may not run in the multi-process mode, and the Search plugins will fail on startup if the server is in multi-process mode.

In the multi-process mode, the server spawns multiple server processes at startup. Each process contains one or more threads (depending on the configuration) that receive incoming requests. Since each process is completely independent, each one has its own copies of global variables, caches, and other resources. Using multiple processes requires more resources from your system. Also, if you try to install an application that requires shared state, it has to synchronize that state across multiple processes. NSAPI provides no helper functions for implementing cross-process synchronization.

When you specify a MaxProcs value greater than 1, the server relies on the operating system to distribute connections among multiple server processes (seeMaxProcs (UNIX/Linux) MaxProcs (UNIX/Linux) for information about the MaxProcs directive). However, many modern operating systems will not distribute connections evenly, particularly when there are a small number of concurrent connections.

Because Sun Java System Web Server cannot guarantee that load is distributed evenly among server processes, you may encounter performance problems if you specify RqThrottle 1 and MaxProcs greater than 1 to accommodate a legacy application that is not thread-safe. The problem will be especially pronounced if the legacy application takes a long time to respond to requests (for example, if the legacy application contacts a backend database). In this scenario, it may be preferable to use the default value for RqThrottle and serialize access to the legacy application using thread pools. For more information about creating a thread pool, refer to the description of the thread-pool-init SAF in the Sun Java System Web Server 6.1 NSAPI Programmer's Guide.

If you are not running any NSAPI in your server, you should use the default settings: one process and many threads. If you are running an application that is not scalable in a threaded environment, you should use a few processes and many threads, for example, 4 or 8 processes and 128 or 512 threads per process.

MaxProcs (UNIX/Linux)

Use this directive to set your UNIX/Linux server in multi-process mode, which may allow for higher scalability on multi-processor machines. If you set the value to less than 1, it will be ignored and the default value of 1 will be used. SeeMulti-Process Mode Multi-Process Mode for a discussion of the performance implications of setting this to a value greater than 1.

Tuning

You can set the value for MaxProcs by:

Note –

You will receive duplicate startup messages when running your server in MaxProcs mode.