What does the Cassandra Trace Sample dashboard display?
The Traces page shows sampled entries from Cassandra's tracing system. Entries with the same query are aggregated and presented by average and maximum sampled duration. Individual query executions, called "sessions", are retrieved along with each execution duration, timestamp, source, consistency level, etc. The internal events generated to process the query are retrievable per session on demand. Tracing is not enabled by default, but nodetool can be used to enable tracing on a portion of all queries with its subcommand "settraceprobability".