How a cache stampede possibly cause problems

• Normal Operation: Facebook, like many large-scale net services, uses caching drastically to improve overall performance.
• Frequently accessed records are saved in a cache, reducing the need to retrieve them from the database whenever.
• Cache Expiration or Invalidation: Due to everyday cache expiration or invalidation regulations, positive cached gadgets want to be refreshed or recomputed.
• Cache Stampede Trigger: When a famous object’s cache expires, more than one person requests simultaneously to try to get admission to the useful resource.
• Resource Intensive Recomputation: The technique of recomputing or regenerating the content for the cache can be aid-extensive, especially for popular items that many users are looking to get admission to simultaneously.
• Increased Load on Resources: The surprising surge in requests for the identical resource can overload the backend systems, inclusive of databases or computation assets.
• Service Degradation or Outage: The extended load and aid contention can result in service degradation or, in intense cases, a service outage.

On September 23, 2010, Facebook experienced one of its most severe outages to date, affecting hundreds of thousands of users internationally. The website online remained inaccessible for over 4 hours, causing extensive disruption and frustration.

The root reason for the outage changed into a cache stampede, a phenomena that happens when a large number of users try to access a cached resource at the same time, overloading the information supply and causing a series of failure.

A cache stampede, also known as cache thrashing or dog-piling, occurs when a massive range of requests try, and get entry to a specific resource that isn’t present inside the cache. This usually takes place when the cached object expires or is invalidated, and multiple requests attempt to repopulate the cache concurrently.