What Is Garbage Collection and Compaction in Data Structure?


Heather Bennett

Garbage collection and compaction are important concepts in data structure that help manage memory efficiently. In this article, we will explore what garbage collection and compaction are and how they work.

Garbage Collection

Garbage collection is the process of automatically reclaiming memory that is no longer in use by a program. When a program creates objects or variables, it allocates memory to store them.

Over time, as the program executes, some objects become unused or unreachable. These unused objects occupy memory space that could be better utilized by other parts of the program.

To solve this problem, garbage collection identifies and frees up memory that is no longer needed. It automatically determines which objects can be safely removed from memory by analyzing their references or pointers.

Advantages of Garbage Collection:

  • Simplifies memory management: Developers don’t have to manually deallocate memory, reducing the risk of memory leaks or dangling pointers.
  • Improves productivity: By automating memory management, developers can focus more on writing code logic rather than worrying about memory deallocation.
  • Prevents crashes: Garbage collection helps prevent crashes caused by accessing invalid or deallocated memory locations.


Compaction is a technique used in garbage collection to optimize the use of available memory space. As objects are created and freed during program execution, gaps may be left between allocated blocks of memory. These gaps can fragment the available memory space, leading to inefficient memory utilization over time.

To counter fragmentation, compaction rearranges the allocated blocks of memory in such a way that all free spaces are contiguous and consolidated. This process involves moving live objects closer together and closing the gaps between them.

Compaction typically involves the following steps:

  1. Identifying live objects that are still in use by the program.
  2. Moving these live objects to a new memory location.
  3. Updating references or pointers to reflect the new memory locations of the moved objects.

Advantages of Compaction:

  • Maximizes memory utilization: Compaction reduces fragmentation, allowing for better usage of available memory space.
  • Improves performance: By reducing fragmentation, compaction can improve memory access times and overall program efficiency.
  • Enables larger allocations: Compacted memory can accommodate larger contiguous allocations, facilitating the creation of larger objects or data structures.


Garbage collection and compaction are essential techniques for managing memory in data structures. Garbage collection ensures that unused objects are automatically released from memory, while compaction optimizes memory utilization by reducing fragmentation.

These techniques improve program efficiency, prevent crashes, and simplify memory management for developers. Understanding garbage collection and compaction is crucial for building robust and efficient software systems.

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