tracing

Module level_filters

Source
Expand description

Trace verbosity level filtering.

§Compile time filters

Trace verbosity levels can be statically disabled at compile time via Cargo features, similar to the log crate. Trace instrumentation at disabled levels will be skipped and will not even be present in the resulting binary unless the verbosity level is specified dynamically. This level is configured separately for release and debug builds. The features are:

  • max_level_off
  • max_level_error
  • max_level_warn
  • max_level_info
  • max_level_debug
  • max_level_trace
  • release_max_level_off
  • release_max_level_error
  • release_max_level_warn
  • release_max_level_info
  • release_max_level_debug
  • release_max_level_trace

These features control the value of the STATIC_MAX_LEVEL constant. The instrumentation macros macros check this value before recording an event or constructing a span. By default, no levels are disabled.

For example, a crate can disable trace level instrumentation in debug builds and trace, debug, and info level instrumentation in release builds with the following configuration:

[dependencies]
tracing = { version = "0.1", features = ["max_level_debug", "release_max_level_warn"] }

§Notes

Please note that tracing’s static max level features do not control the log records that may be emitted when tracing’s “log” feature flag is enabled. This is to allow tracing to be disabled entirely at compile time while still emitting log records — such as when a library using tracing is used by an application using log that doesn’t want to generate any tracing-related code, but does want to collect log records.

This means that if the “log” feature is in use, some code may be generated for log records emitted by disabled tracing events. If this is not desirable, log records may be disabled separately using log’s static max level features.

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