In Java, garbage collection is an important feature that automatically frees up memory that is no longer being used by an application. The Java Virtual Machine (JVM) has different garbage collection algorithms to manage memory, and two of the popular ones are the Concurrent Mark and Sweep (CMS) collector and the Parallel collector.
The CMS collector is designed to minimize pauses in the application by running concurrently with the application threads. It works by dividing the heap into multiple regions, and scanning them in parallel to mark the objects that are still in use. After the marking phase is completed, the collector performs a sweep phase to reclaim the memory that is not being used. During the CMS collector’s mark phase, the application threads continue to run, and any changes made to the object graph are recorded, so that the collector can update its records before the sweep phase.
On the other hand, the Parallel collector is designed to maximize the throughput of the application by utilizing all available CPU resources to complete the garbage collection process as quickly as possible. It works by dividing the heap into multiple regions and scanning them in parallel. During the parallel scanning phase, all application threads are paused, which can result in longer pauses, but the overall garbage collection process is completed more quickly.
Here is an example of how to set the garbage collection algorithm to the CMS collector:
java -XX:+UseConcMarkSweepGC MyApp
And here is an example of how to set the garbage collection algorithm to the Parallel collector:
java -XX:+UseParallelGC MyApp
It is important to note that the choice of garbage collector algorithm depends on the specific needs of the application. The CMS collector is ideal for applications that require low-latency and short pauses, while the Parallel collector is better suited for applications that require high throughput and can tolerate longer pauses.