Java Garbage Collection Tuning. Java theory and practice: Garbage collection in the HotSpot JVM. Last month, we looked at the classic garbage collection techniques of reference counting, copying, mark-sweep, and mark-compact. Each of these approaches has advantages and disadvantages in certain situations. For example, copying does well when a large proportion of objects are garbage, but does poorly with many long-lived objects (copying them repeatedly). Conversely, mark-compact does quite well with long-lived objects (copying them only once), but not so well with many short-lived objects. The technique used by the 1.2 and later JVMs, called generational garbage collection, combines these two techniques to get the best of both worlds, and as a bonus provides very low object allocation overhead. Old objects, young objects In any application heap, some objects become garbage shortly after their creation, some survive for a long time and then become garbage, and others can remain live for the entirety of the program's run.
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[Editor's note: the following article was submitted by Sathiskumar Palaniappan, Kavitha Varadarajan, and Jayashree Viswanathan.] Introduction Many server applications, such as Web servers, application servers, database servers, file servers, and mail servers, maintain worker queues and thread pools to handle large numbers of short tasks that arrive from remote sources. In general, a "worker queue" holds all the short tasks that need to be executed, and the threads in the thread pool retrieve the tasks from the worker queue and complete the tasks. Since multiple threads act on the worker queue, adding tasks to and deleting tasks from the worker queue needs to be synchronized, which introduces contention in the worker queue.
This article explains the contention involved with the traditional approach (using a common queue for the thread pool) and helps you reduce the contention by maintaining one queue per thread. Common Worker Queue: The Traditional Approach Figure 1. Listing 1. Figure 2.