nodetool settraceprobability

Sets the probability for tracing a request.

Sets the probability for tracing a request.


nodetool <options> settraceprobability -- <value>
Table 1. Options
Short Long Description
-h --host Hostname or IP address
-p --port Port number
-pwf --password-file Password file path
-pw --password Password
-u --username User name
Other options are:
  • value is a probability between 0 and 1.


Probabilistic tracing is useful to determine the cause of intermittent query performance problems by identifying which queries are responsible. This option traces some or all statements sent to a cluster. Tracing a request usually requires at least 10 rows to be inserted.

A probability of 1.0 will trace everything whereas lesser amounts (for example, 0.10) only sample a certain percentage of statements. Care should be taken on large and active systems, as system-wide tracing will have a performance impact. Unless you are under very light load, tracing all requests (probability 1.0) will probably overwhelm your system. Start with a small fraction, for example, 0.001 and increase only if necessary. The trace information is stored in a system_traces keyspace that holds two tables – sessions and events, which can be easily queried to answer questions, such as what the most time-consuming query has been since a trace was started. Query the parameters map and thread column in the system_traces.sessions and events tables for probabilistic tracing information.