You can tune thread pool settings by following the instructions in Chapter 5, Administering Thread Pools, in Oracle GlassFish Server 3.1 Administration Guide. If using the Administration Console Thread Pool settings are available on the Configurations->configuration-name->Thread Pools->thread-pool-name page.
The following thread pool settings can have significant effects on GlassFish Server performance:
The Max Thread Pool Size parameter specifies the maximum number of simultaneous requests the server can handle. The default value is 5. When the server has reached the limit or request threads, it defers processing new requests until the number of active requests drops below the maximum amount. Increasing this value will reduce HTTP response latency times.
In practice, clients frequently connect to the server and then do not complete their requests. In these cases, the server waits a length of time specified by the Timeout parameter.
Also, some sites do heavyweight transactions that take minutes to complete. Both of these factors add to the maximum simultaneous requests that are required. If your site is processing many requests that take many seconds, you might need to increase the number of maximum simultaneous requests.
Adjust the thread count value based on your load and the length of time for an average request. In general, increase this number if you have idle CPU time and requests that are pending; decrease it if the CPU becomes overloaded. If you have many HTTP 1.0 clients (or HTTP 1.1 clients that disconnect frequently), adjust the timeout value to reduce the time a connection is kept open.
Suitable Request Max Thread Pool Size values range from 100 to 500, depending on the load. If your system has extra CPU cycles, keep incrementally increasing thread count and monitor performance after each incremental increase. When performance saturates (stops improving), then stop increasing thread count.
The Min Thread Pool Size property specifies the minimum number of threads the server initiates upon startup. The default value is 2. Min Thread Pool Size represents a hard limit for the maximum number of active threads that can run simultaneously, which can become a bottleneck for performance.
Specifying the same value for minimum and maximum threads allows GlassFish Server to use a slightly more optimized thread pool. This configuration should be considered unless the load on the server varies quite significantly.