cache miss
also: cache fault
A cache miss occurs when the CPU or system requests data that is not currently stored in the cache, requiring slower access from main memory or disk. This is the opposite of a cache hit.
A cache miss forces the system to retrieve data from a slower storage level—typically main memory (RAM) or disk—instead of the fast CPU cache. This significantly increases access time and reduces performance.
For example, if a program repeatedly accesses the same array of 1 million integers that doesn't fit in L3 cache, many of those accesses will be cache misses. Each miss stalls the CPU while it waits for data from RAM, which can be 100+ times slower than cache access.
Developers optimize for cache hits by improving locality of reference—accessing nearby memory locations in sequence rather than jumping around randomly. Cache hit rates are a critical performance metric monitored with tools like perf on Linux.