What It Costs When It Fails
Without caching, every request hits your application and database. With caching, the vast majority of requests are served from memory without touching either. The difference is not marginal. A properly implemented caching architecture can handle ten times the traffic on the same hardware. The cost of getting it wrong is a server that falls over the first time you send significant traffic to it.
Caching is the practice of storing the results of expensive operations so that subsequent requests for the same result can be served from the stored copy rather than repeating the operation. In web infrastructure, expensive operations include database queries, PHP execution, and file system reads. Caching reduces the load on each of these systems and dramatically increases the number of requests a given server can handle.
The layers of caching in a typical web stack include opcode caching (storing compiled PHP bytecode), object caching (storing database query results and computed values), full-page caching (storing complete rendered HTML responses), and CDN caching (storing static assets at edge locations close to users). Each layer serves a different purpose and operates at a different level of the stack.
Cache Invalidation
Cache invalidation is the process of removing or updating cached data when the underlying data changes. It is one of the genuinely hard problems in computer science, not because the concept is complex, but because the edge cases are numerous and the consequences of getting it wrong are visible to users. A user who sees stale content after making a change, or who sees different content than another user due to cache inconsistency, has a poor experience that reflects on the application, not the cache.
"What caching layers are currently implemented in our stack, what is the cache hit rate, and what happens to our server when the cache is cold?"
HostRoman implements a minimum of three caching layers for every application: full-page cache for static content, object cache for database query results, and opcode cache for PHP compilation. Cache hit rates are monitored continuously. Cache warming procedures are documented and tested. We validate cache behaviour under load before any significant traffic event.