The version control service for ATLAS data acquisition configuration files

To configure data taking session the ATLAS systems and detectors store more than 160 MBytes of data acquisition related configuration information in OKS XML files [1]. The total number of the files exceeds 1300 and they are updated by many system experts. In the past from time to time after such updates we had experienced problems caused by XML syntax errors or inconsistent state of files from a point of view of the overall ATLAS configuration. It was not always possible to know who made a modification causing problems or how to go back to a previous version of the modified file. Few years ago a special service addressing these issues has been implemented and deployed on ATLAS Point-1. It excludes direct write access to XML files stored in a central database repository. Instead, for an update the files are copied into a user repository, validated after modifications and committed using a version control system. The system's callback updates the central repository. Also, it keeps track of all modifications providing a Web interface for browsing details of the modifications or restoring any previous version of files. This paper provides details of implementation and exploitation experience that maybe interesting for others using various files for configuration purposes.