cachessia

Cachessia is a fictional term sometimes used in computer science education and speculative literature to describe a syndrome of cache memory degradation under certain workloads. It denotes a range of effects that collectively reduce cache efficiency and system performance, particularly in multi-level, multi-core, or distributed cache environments. While not an established diagnosis in real-world practice, cachessia serves as a metaphor for the sorts of problems that can arise when cache resources become overwhelmed or poorly coordinated.

Etymology and scope: the name cachessia is a blend of cache and the suffixes found in medical terms such as cachexia, chosen to emphasize the idea of wasting or diminishing cache effectiveness rather than a literal disease. It is used chiefly as a teaching device or in thought experiments to discuss memory hierarchy challenges rather than as a formal concept.

Causes and symptoms: cachessia can arise from high contention for shared caches, aggressive or ill-timed eviction policies, inefficient cache-coherence protocols, and pathological thrashing where small data items continuously move between caches. Symptoms typically include rapidly falling cache hit rates, rising miss penalties, increased coherence traffic, higher memory latency, CPU stalls, and volatile performance that depends on workload timing and data placement.

Mitigation: addressing cachessia involves cache-aware design and workload management. Strategies include partitioning caches to reduce contention, refining eviction policies, leveraging private versus shared cache configurations, improving data locality and alignment, software-managed caching where appropriate, and workload shaping to minimize thrashing and coherence overhead.

Context and limitations: cachessia is not an official term in standards or practice, but it is used to illustrate how cache design and memory access patterns can impact performance. See also cache coherence, cache thrashing, and false sharing.