Cache Hit Rate Collapse Amplifying Disk IO
warningLow cassandra_key_cache_hit_rate forces Cassandra to read row locations from disk on every query instead of memory, multiplying disk IO. Degraded cache performance appears as read latency increases without corresponding write load changes.
Monitor cassandra_key_cache_hit_rate dropping below baseline (typically 85-95%). Correlate with increasing cassandra_client_request_read_time_50p and disk IO metrics showing elevated read operations despite stable query volume.
Increase key cache size allocation if memory permits. Investigate workload changes causing cache evictions (e.g., scanning new data ranges). Check if partition count increased significantly, requiring larger cache footprint. If row cache exists, evaluate whether its memory would be better allocated to key cache.