Tracing must be turned on by the DBA. It is not always used during normal database operation, rather, it is intended as a debugging tool. Clients should be informed that tracing is not free, requiring at least 10 rows to be inserted per traced operation. It is possible to set full tracing on during an interactive cqlsh shell session, though this is not the method to be used. Rather, probabilistic tracing should be enabled using the nodetool utility. The trace probability is set to a value between 0 and 1, inclusive, such that only a certain percentage of database operations are profiled.
The Cassandra documentation recommends starting with a value of 0.001 and increasing as appropriate to prevent burdening the server. The following command sets the trace probability, where are the usual host, port, username, password, and is the trace probability:
nodetool settraceprobability
