nodetool settraceprobability

Sets the probability for tracing a request.

Synopsis

nodetool <options> settraceprobability -- <value>

Options are:
- ( -h | --host ) <host name> | <ip address>
- ( -p | --port ) <port number>
- ( -pw | --password ) <password >
- ( -u | --username ) <user name>
- ( -pwf <passwordFilePath | --password-file <passwordFilePath> )
-- separates an option and argument that could be mistaken for a option.
value is a probability between 0 and 1.

Description

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.

To discover the current trace probability setting, use nodetool gettraceprobability.