Is LRU the best Cache Eviction Policy?

Whether LRU (Least Recently Used) is the best eviction policy depends on the specific requirements and characteristics of the system. LRU (Least Recently Used) is often considered a good eviction policy in the following cases:

1. Temporal Locality

When there is a temporal locality in the access patterns, meaning that recently accessed items are likely to be accessed again soon. LRU leverages this characteristic by keeping recently accessed items in the cache, improving cache hit rates.

2. Stable Working Set

When the working set of the application is relatively stable and does not change frequently. LRU is effective in this scenario because it tends to retain items that are frequently accessed over time, adapting well to stable access patterns.

3. Simple Implementation

When simplicity and ease of implementation are important factors. LRU has a straightforward implementation compared to some other eviction policies, making it a popular choice in many systems.

4. Performance Trade-offs

When the performance trade-offs of LRU align with the application requirements. While LRU may not be optimal in all scenarios, its performance characteristics make it a good default choice for many applications.

5. Cost-Effective

LRU is often more cost-effective than other eviction policies that require more complex data structures or tracking mechanisms. The simplicity of LRU can lead to lower memory and processing overhead compared to more sophisticated policies.

6. Cache Locality

LRU tends to exhibit good cache locality, meaning that it is more likely to keep items in the cache that are close to each other in memory. This can improve memory access patterns and reduce cache misses.

7. Compatibility with Caching Libraries

Many caching libraries and systems default to or are optimized for LRU eviction. Using LRU can therefore be beneficial in terms of compatibility and interoperability with existing caching solutions.

Overall, LRU’s simplicity, cost-effectiveness, cache locality, and compatibility with certain access patterns make it a suitable choice for many applications, particularly those with predictable and stable access patterns.