numass-framework/dataforge-core/docs/logging.md

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Logging and History

DataForge supports two separate logging system:

1. Generic logging system based on slf4j on JVM and possibly any other native logging on remote platform. It is used for debugging and online information about the process. Logger could be obtained in any point of the program (e.g. via LoggerFactrory.getLogger(...) in JVM). Critical elements and all ContextAware blocks automatically have a pre-defined logger accessible via logger property.

2. Internal logging utilizes hierarchical structure called History. Each Hisotory object has a reference to Chronocle which stores history entries called Record. Also any History but the root one which is Global.history must have a parent History. Any Record entry appended to the history is automatically appended to its parent with appropriate trace element which specifies where it entry comes from. One can also attach hooks to any chronicle to be triggered on entry addition. Global history logging behavior is controlled via Chronicler context plugin, which is loaded by default into Global context. History ususally could not be created on sight (only from context chronicler) and should be passed to the process explicitly.

The key difference between logger and history is that logs are intended for debugging and information and are discarded after being read. The history on the other hand is supposed to be the important part of the analysis and should be stored with analysis results after it is complete. It is strongly discouraged to use History in a performance-sensitive code. Also it is bad idea to output any sensitive information to log since it could be discarded.