Least recently used

Definition

Least Recently Used (LRU) is a cache replacement policy that evicts the least recently accessed data when new data needs to be loaded into the cache. This strategy assumes that data accessed more recently will likely be accessed again soon, while older data may no longer be relevant. LRU helps to optimize cache performance by maintaining frequently used data and minimizing cache misses.

5 Must Know Facts For Your Next Test

1. LRU can be implemented using a variety of data structures, such as linked lists or hash maps, to track the order of access.
2. In LRU, when a cache hit occurs, the accessed item is moved to the front of the order, while items that haven't been accessed for a while are moved back.
3. LRU is more effective in scenarios where the access pattern exhibits temporal locality, meaning that recently accessed items are likely to be accessed again soon.
4. An efficient implementation of LRU may have an overhead in terms of time complexity, as it requires updating the order of access each time an item is accessed.
5. In some cases, approximate LRU implementations can be used to reduce overhead, sacrificing some accuracy for performance gains.

Review Questions

• How does the Least Recently Used (LRU) replacement policy improve cache performance?
  • The Least Recently Used (LRU) replacement policy improves cache performance by prioritizing data that has been accessed recently. By evicting the least recently used items, LRU assumes that this data is less likely to be needed again soon. This approach reduces the chance of cache misses since frequently accessed data remains in the cache longer, ultimately leading to faster data retrieval times.
• What are some potential drawbacks of using the LRU replacement policy in cache management?
  • While LRU is effective, it has potential drawbacks such as increased overhead due to maintaining access order, which can lead to slower performance in high-throughput situations. Furthermore, in cases where access patterns are less predictable or exhibit significant changes, LRU may not perform optimally, potentially resulting in unnecessary evictions of items that could still be relevant.
• Evaluate how the implementation of Least Recently Used (LRU) compares with other cache replacement policies like FIFO or LFU in terms of efficiency and performance.
  • Evaluating LRU against other policies like FIFO (First In, First Out) or LFU (Least Frequently Used) reveals that LRU often provides superior efficiency in scenarios with temporal locality due to its focus on recent usage patterns. While FIFO may result in frequent evictions of still-relevant data simply because it was loaded first, LFU can struggle if popular items become less relevant over time. However, LRU's maintenance of access order can introduce overhead compared to simpler policies like FIFO. In general, choosing the best policy depends on specific workload characteristics and access patterns.

Related terms

Cache Hit: A situation where the requested data is found in the cache, resulting in faster access times.

Cache Miss: Occurs when the requested data is not found in the cache, requiring retrieval from a slower memory source.

Replacement Policy: The strategy used to determine which data to remove from the cache when new data needs to be loaded.