Cache Invalidation

1. What exactly is Cache Invalidation?

Your support chatbot caches its most common answers in Azure Cache for Redis, so the same question asked thousands of times doesn't trigger a fresh Azure AI Search lookup and a new Azure OpenAI call every time. Each cached answer is set to expire after a fixed period, say 24 hours.

Now a company updates one of its help articles partway through that period, widening a return window from 30 to 60 days, say. The cache has no way to know the article changed. It keeps serving the old answer to every matching question until the fixed period finally runs out on its own, hours after the article was already correct.

The cache doesn't know the source content changed. It just waits out the clock it was given, whether or not that clock still matches reality. That's exactly what cache invalidation fixes.

2. How would you fix it in .NET/Azure?

Cache invalidation reacts the moment things change, instead of waiting on a timer: keep the fixed expiration on Azure Cache for Redis as a safety net, not the main defense, and when a company edits a help article, delete the Redis entries built from that article right away, in the same step as the edit. The next matching question then finds nothing cached and goes to Azure AI Search and Azure OpenAI fresh, picking up the edit immediately instead of after the clock runs out.

Use: StackExchange.Redis (DEL)

A cache that clears itself the moment the truth changes beats a cache that only clears itself on a timer.

3. How can you visualize it in everyday terms?

A carton of milk in the fridge has a printed expiration date, so you know roughly when to throw it out even if nobody tells you anything else.

But if a fresh carton arrives today, you don't wait for the old one's printed date. You throw the old one out right now, because you know it's been replaced.

Act the moment you know something changed, not on a date printed days in advance.