Threadpool Saturation Blocking New Requests
warningCassandra's SEDA architecture relies on threadpools for async processing. When cassandra_thread_pool_count_blocked_tasks or cassandra_thread_pool_currently_blocked_tasks accumulate, requests queue waiting for threads, causing latency spikes that don't correlate with CPU/disk saturation.
Alert when cassandra_thread_pool_count_blocked_tasks grows consistently or cassandra_thread_pool_currently_blocked_tasks stays above zero for extended periods. Cross-reference with cassandra_thread_pool_active_tasks approaching threadpool max size.
Identify which threadpool is saturated (read, write, compaction). If sustained high load, add nodes to distribute work. If temporary spike, increase threadpool size cautiously or reduce incoming request rate. Check for slow queries or hot partitions causing thread starvation in specific pools.