This document provides guidance on diagnosing problems in Cassandra production systems. It recommends first using OpsCenter to identify issues, then monitoring servers, applications, and logs. Common problems discussed include incorrect timestamps, tombstones slowing queries, not using a snitch, version mismatches, and disk space not being reclaimed. Diagnostic tools like htop, iostat, and nodetool are presented. The document also covers JVM garbage collection profiling to identify issues like early object promotion and long minor GCs slowing the system.