Difference between Cache Invalidation and Cache Eviction

Last Updated : 23 Oct, 2024

Cache Invalidation is the process of removing or marking cache entries as outdated when the main database is updated, making sure users always receive fresh data. Cache Eviction, on the other hand, removes older or less frequently accessed data from the cache to free up space for new data, typically based on certain eviction policies like LRU (Least Recently Used).

Cache-Invalidation-vs-Cache-Eviction — Cache Invalidation vs. Cache Eviction

Table of Content

What is Cache Invalidation?

Cache invalidation is the process of marking or removing stale data in the cache when the data in the main database is updated. It make sure that the cache holds the most up to date information by removing old data.

Advantages:
- Make sure fresh and accurate data in the cache.
- It helps in maintaining consistency between cache and database.
- It reduces the risk of serving stale data to users.
Disadvantages:
- It can add complexity to manage invalidation rules.
- May cause slight delays when frequently updating data.
- It requires careful handling in distributed systems to avoid conflicts.

What is Cache Eviction?

Cache eviction is the process of removing old or less frequently used data from the cache to free up space for new data. It is based on eviction policies like Least Recently Used (LRU) or First In, First Out (FIFO).

Advantages:
- It helps in efficiently managing cache size.
- Improves memory usage by automatically removing old data.
- Keeps the cache optimized for storing frequently accessed data.
Disadvantages:
- It can remove important data if the eviction policy is not appropriate.
- May lead to performance issues if frequently accessed data is evicted.
- Fetching again deleted data from the main database can cause delays.

Differences between Cache Invalidation and Cache Eviction

Below are the differences between cache invalidation and cache eviction:

Aspect	Cache Invalidation	Cache Eviction
Purpose	Make sure fresh data by removing outdated cache entries.	Frees up cache space by removing old or less used data.
When Triggered	When data in the main database changes.	When the cache is full or based on predefined policies.
Focus	Focuses on data freshness and consistency.	Focuses on cache size management.
Policies Used	No specific policy and invalidates based on data updates.	Uses policies like LRU, FIFO, or LFU for removal.
Type of Data Removed	Removes outdated or stale data.	Removes less frequently used or old data.
Complexity	More complex to implement due to data consistency rules.	Simpler to implement, but choosing the right policy can be tricky.
Impact on Performance	May increase latency when fetching fresh data from the database.	Improves cache performance by keeping frequently accessed data.
Risk	Risk of serving outdated data if not done correctly.	Risk of evicting frequently accessed data if policies are not efficient.

Conclusion

Cache invalidation ensures that the data in the cache remains fresh and consistent with the main database, while cache eviction focuses on managing the cache's size by removing old data. Both techniques are important in cache management but serve different purposes.