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Data logging: overview

This page describes the kinds of data that midas can record (event data, time series, images and run information), and the mlogger program that records them.

Data types

Midas provides tools for logging several types of data:

  • event data (e.g. waveforms, particle time-of-flight, number of particles seen) gets logged in midas files, which are written to disk and can later be analysed by users.
  • time series data (e.g. temperatures and voltages vs time) gets logged by the history system, and stored either in binary files or in an SQL database. Webpages are provided for viewing plots/trends, and the data can also be analysed by users later.
  • image data (e.g. webcam images vs time) can be recorded to disk and then replayed on a webpage.
  • run-level information (e.g. start/stop times and critical configuration parameters) can be logged in either a text file or an SQL database, so analysers can later search for the data of interest.
Event data Time series data Image data Run info
Data format Midas events Value vs time Images Summary info
Read from Event buffers ODB Webcam ODB
Write to binary files Midas files Custom format jpg, png, gif etc
Write to text files ✔
Write to SQL database ✔ ✔
Built-in web display Low-level debugging Interactive plots Interactive browsing
Tools for custom web pages Built-in Built-in Built-in
Tools for C++/python data analysis Built-in Built-in Easy to write

The mlogger program

All four types of data are handled by the mlogger program. You can start mlogger using mlogger (to have it run in the foreground) or mlogger -D (to have it run in the background).

mlogger will create the /Logger and /History/Images portions of the ODB the first time it is started. All configuration is done via the ODB. The rest of the /History ODB directory handles displaying history data in web pages, and is created by mhttpd (the midas web server).

The ODB settings are split up as:

Related pages

midas files Run log Archiving /Logger keys mlogger