LoggingLevels

LoggingLevels, also called log levels, are a mechanism used in software systems to categorize the importance of log messages and to control which messages are recorded or displayed. They enable developers and operators to balance the need for information with performance and storage considerations.

Common levels include TRACE, DEBUG, INFO, WARNING (or WARN), ERROR, and CRITICAL (or FATAL). The exact names and the ordering may vary by framework, but the typical order from most verbose to least is TRACE, DEBUG, INFO, WARNING, ERROR, CRITICAL. Some systems include additional levels or combine lower ones into verbose categories.

How level filtering works: A logger or handler is configured with a threshold level. Messages with a severity at least as high as the threshold are emitted; those below are ignored. For example, a logger set to INFO will emit INFO, WARNING, ERROR, and CRITICAL messages but ignore DEBUG and TRACE. Levels may be configured per logger or per handler, and levels can be changed at runtime in many frameworks.

In many frameworks, loggers form a hierarchy based on component or module names, and child loggers may inherit the level from their parents unless overridden. Levels are numeric in some implementations and symbolic in others. The use of levels supports production-grade logging by enabling verbose logs during development and concise logs in production. Best practices encourage selecting an appropriate minimum level and avoiding overly verbose levels in production.