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The Virtual Machine for the Java platform (Java Virtual Machine) or JVM machine) can support many threads of execution simultaneously. To help performance, GlassFish Server maintains one or more thread pools. It is possible to assign specific thread pools to connector modules, to network listeners, or to the Object Request Broker (ORB).

One thread pool can serve multiple connector modules and enterprise beans. Request threads handle user requests for application components. When GlassFish Server receives a request, it assigns the request to a free thread from the thread pool. The thread executes the client's requests and returns results.

Administrators will have to continuously observe the request load on their applications, periodically check how the thread pool services these requests, and accordingly decide whether/not to resize the thread pool commensurate to the current and anticipated load. The GfThreadPoolTest test provides administrators with the load and thread pool usage insights they require to take these crucial sizing decisions.

Measurement	Description	Measurement Unit	Interpretation
Core_threads	Indicates the number of core threads currently in this pool.	Number
Current_thread_count	Indicates the current number of request processing threads in this pool.	Number
Busy_thread_count	Indicates the number of request processing threads that are currently busy in this pool.	Number
Max_thead_count	Indicates the maximum number of threads allowed in this thread pool.	Number	This measure reports the value of the Max Thread Pool Size parameter of the GlassFish Enterprise server. This 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.
Total_executed_tasks	Indicates the total number of tasks executed by the threads in this pool during the last measurement period.	Number	This measure is a good indicator of how busy the pool was during the last measurement period.
Thread_busy_percent	Indicates the percentage of threads in this pool that are currently in use.	Percent	This measure is computed using the following formula: (Current busy threads / Maximum threads)100* A high value is indicative of a busy pool. A value close to 100% indicates excessive utilization of threads in a pool. If the value of this measure grows closer to 100% over time, it indicates that the pool is rapidly running out of threads to service the request load. You may then have to fine-tune the thread pool size using the Max Thread Pool Size parameter and the Min Thread Pool Size parameter. 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. 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.
Pool_utilization	Indicates the percentage of threads in the pool that are active.	Percent	This measure is computed as a ratio of the value of the Current_thread_count measure and the Max_thead_count measure.