Cache Invalidation Storm – When Your Cache Eviction Overwhelms the Backend

The Scenario: The Cache Crashed the Party

The caches you’ve implemented are keeping your app lightning-fast. Life is good. Then out of nowhere: slowdown. Massive slowdown. Response times crawl. Your database is gasping for air. And users? They’re feeling the pain.

You investigate – and there it is: A large chunk of your cache was invalidated at once. The result? A thundering herd of requests flooding your backend to rebuild the cache. And just like that, you’ve been hit by a cache invalidation storm. It’s sudden, it’s intense and it leaves your infrastructure scrambling.

The Quick-Fix: Break the Wave

To stop the bleeding, you need to reduce the pressure on the backend – fast.

• Throttle incoming requests to slow the pace at which the backend gets hit
• Stagger rebuilds by introducing slight delays to prevent everything from hitting at once
• Temporarily scale up backend capacity to absorb the sudden spike

Crisis contained! These measures won’t fix the issue long-term, but they’ll buy you some time to stabilize the system while you work on a permanent solution.

Understanding the Pattern – and Breaking It

A cache invalidation storm is what happens when too much cached data expires at once. This triggers an avalanche of backend requests to rebuild those entries – often all at the same time. The result is degraded performance, and in severe cases, full-on outages.

This is more common than you’d think, especially in systems that rely heavily on caching for performance but treat invalidation as an afterthought.

The Real Fix: Rethink Cache Invalidation

“Cache Invalidation Storms” don’t come out of nowhere – they’re the result of flawed invalidation strategies that treat all data as if it expires at the same time. The key to preventing the next storm lies in smarter caching patterns:

• Stagger expirations → Vary TTLs to avoid synchronized invalidation.
• Lazy loading → Only rebuild cache entries when they’re actually requested, not all at once.
• Cache key versioning → Roll out updates gradually instead of invalidating entire caches at once.
• Pre-warming → Rebuild critical cache entries proactively before they expire to soften the load.

In Short:

A cache invalidation storm isn’t just bad luck – it’s often a predictable result of how caching is handled. With a few smart adjustments to expiration patterns, loading behavior, and cache versioning, you can avoid backend overload and keep performance steady – even when the cache gets flushed.

So: tweak your strategy, keep your backend happy, and give your cache some love.

Stay tuned,
Matthias

This blog post is part of our multi-part series, where we describe common software outages and help you resolve them quickly. You can find all other posts under Foreword: Navigating the Storms of Software Outages.