21. **Explain the difference between absolute and sliding expiration in ASP.NET caching.**
- **Absolute expiration:** Specifies a fixed duration for which cached data remains valid. After the expiration duration elapses, the cached item is considered stale and needs to be refreshed.
- **Sliding expiration:** Resets the expiration duration each time the cached item is accessed. As long as the item is accessed within the specified sliding expiration period, it remains valid. Sliding expiration is useful for scenarios where data needs to be cached as long as it's actively being used.
22. **What is cache invalidation and why is it important?**
Cache invalidation refers to the process of removing stale or outdated cached items from the cache to ensure that only fresh and relevant data is served to users. It's important to maintain cache integrity and prevent users from accessing outdated information.
23. **How do you implement cache invalidation strategies in ASP.NET applications?**
Cache invalidation strategies can include setting appropriate expiration policies, using cache dependencies to monitor changes in underlying data, implementing manual cache invalidation mechanisms, and utilizing cache-clearing techniques when necessary.
24. **Explain the concept of cache stampede and how to mitigate it in ASP.NET applications.**
Cache stampede, also known as cache thrashing, occurs when multiple requests concurrently attempt to access the same cached item that has expired or been evicted. This can overload the server and degrade performance. Mitigation strategies include using mutexes or locks to prevent simultaneous cache refreshes, implementing staggered expiration times, and employing caching patterns like lazy loading.
25. **What are cache aside (lazy loading) and read-through caching patterns?**
- **Cache aside (lazy loading):** In this pattern, the application first checks the cache for the requested data. If the data is not found in the cache, it is fetched from the underlying data source, added to the cache, and then returned to the caller. Subsequent requests for the same data will be served from the cache.
- **Read-through caching:** In this pattern, the application does not directly interact with the cache. Instead, it relies on a caching layer or framework to automatically fetch data from the underlying data source when requested data is not found in the cache. The retrieved data is then cached for future access.
26. **What are cache regions and how are they used in ASP.NET caching?**
Cache regions allow developers to logically partition cached items into separate groups or namespaces, enabling finer-grained control over cache management and expiration. This helps organize cached data and prevent namespace collisions in multi-tenant or distributed caching scenarios.
27. **Explain the concept of cache coherency and how it relates to distributed caching.**
Cache coherency refers to the consistency and synchronization of cached data across multiple cache instances or nodes in a distributed caching environment. Maintaining cache coherency ensures that all cache replicas have an up-to-date view of the data and prevents inconsistencies or data staleness.
28. **What are cache-through and write-through caching patterns?**
- **Cache-through caching:** In this pattern, data is first written to the underlying data source, and then the cache is updated with the newly written data. Subsequent reads for the same data will be served from the cache.
- **Write-through caching:** In this pattern, data is written to both the cache and the underlying data source simultaneously or in a coordinated manner. This ensures that the cache is always synchronized with the data source, maintaining consistency between cached data and the authoritative data source.
29. **Explain the role of cache size and cache eviction policies in ASP.NET caching.**
Cache size and eviction policies determine how cached items are managed and removed from memory when the cache reaches its maximum capacity. Eviction policies define rules for selecting which items to remove, such as least recently used (LRU), least frequently used (LFU), or based on custom criteria.
30. **How do you handle cache warming in ASP.NET applications?**
Cache warming involves pre-populating the cache with frequently accessed or critical data during application startup or idle periods to ensure that the cache is primed and ready to serve requests efficiently. This can be achieved using background tasks, scheduled jobs, or proactive cache loading mechanisms.