What does CMS mean in JAVA
CMS stands for Concurrent Mark Sweep, a garbage collection technique used in Java virtual machines (JVMs) to manage memory and automatically reclaim unused objects. It combines the mark-and-sweep algorithm with concurrent marking to improve performance by minimizing pauses during garbage collection.
CMS meaning in Java in Computing
CMS mostly used in an acronym Java in Category Computing that means Concurrent Mark Sweep
Shorthand: CMS,
Full Form: Concurrent Mark Sweep
For more information of "Concurrent Mark Sweep", see the section below.
CMS Operation
CMS works by dividing the Java heap into two regions: a young generation and an old generation. Young objects are allocated in the young generation, while long-lived objects are promoted to the old generation.
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Marking Phase (Concurrent):
- CMS marks live objects in the young generation concurrently with the running application.
- This marking happens without pausing the application, reducing the impact on performance.
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Sweep Phase (Concurrent):
- Once marking is complete, CMS identifies and reclaims unreachable objects in the young generation while the application continues running.
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Old Generation Collection (Stop-the-World):
- When the young generation fills up, CMS triggers a stop-the-world collection.
- The application pauses briefly while CMS marks and sweeps the old generation, removing unreachable objects.
Benefits of CMS
- Reduced GC Pauses: Concurrent marking and sweeping minimize pauses during garbage collection, improving application responsiveness.
- High Throughput: CMS allows the application to continue running during GC, increasing overall system throughput.
- Scalability: CMS can handle large heaps and is suitable for applications with high memory consumption.
Limitations of CMS
- Fragmentation: CMS can lead to memory fragmentation, which can impact performance over time.
- Stop-the-World Collections: Old generation collections still require stop-the-world pauses, which can be noticeable for latency-sensitive applications.
- Memory Overhead: CMS maintains additional data structures for concurrent marking, which can consume some memory.
Essential Questions and Answers on Concurrent Mark Sweep in "COMPUTING»JAVA"
What is Concurrent Mark Sweep (CMS)?
Concurrent Mark Sweep (CMS) is a garbage collection algorithm used in Java Virtual Machines (JVMs) to reclaim unused memory space. It runs concurrently with the application, allowing the application to continue executing while garbage collection is performed in the background.
How does CMS work?
CMS divides the heap into several memory segments called "young" and "old" generations. It marks live objects in the young generation during minor collections and promotes them to the old generation if they survive multiple collections. Old generation objects are marked and swept during major collections.
What are the advantages of using CMS?
CMS offers several advantages, including:
- Concurrency: It runs concurrently with the application, minimizing application pauses.
- Predictable pauses: Major collections are less frequent and more predictable compared to other garbage collectors.
- Scalability: It can handle large heaps, making it suitable for large applications.
What are the disadvantages of using CMS?
CMS has some disadvantages, such as:
- Space overhead: It requires additional memory space for its internal data structures.
- Pause duration: Major collections can still cause significant pauses in application execution.
- Fragmentation: It can lead to memory fragmentation, which may affect application performance.
When is CMS a good choice?
CMS is a good choice for applications that:
- Require low and predictable garbage collection pauses.
- Have large heaps.
- Can tolerate some space overhead.
Final Words: CMS is a widely used garbage collection technique that provides a balance between performance and scalability for Java applications. By minimizing pauses and allowing concurrent processing, CMS improves application responsiveness and throughput. However, it is important to consider its limitations and tune parameters to optimize performance in specific scenarios.
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