Utility of collecting metadata to manage a large scale conditions database in ATLAS

International audienceThe ATLAS Conditions Database, based on the LCG Conditions Database\ninfrastructure, contains a wide variety of information needed in online data taking and\noffline analysis. The total volume of ATLAS conditions data is in the multi-Terabyte\nrange.\n\nInternally, the active data is divided into 65 separate schemas (each with hundreds of\nunderlying tables) according to overall data taking type, detector subsystem, and\nwhether the data is used offline or strictly online. While each schema has a common\ninfrastructure, each schema's data is entirely independent of other schemas, except at\nthe highest level, where sets of conditions from each subsystem are tagged globally for\nATLAS event data reconstruction and reprocessing.\n\nThe partitioned nature of the conditions infrastructure works well for most purposes, but\nmetadata about each schema is problematic to collect in global tools from such a\nsystem because it is only accessible via LCG tools schema by schema. This makes it\ndifficult to get an overview of all schemas, collect interesting and useful descriptive and\nstructural metadata for the overall system, and connect it with other ATLAS systems.\nThis type of global information is needed for time critical data preparation tasks for data\nprocessing and has become more critical as the system has grown in size and diversity.\n\nTherefore, a new system has been developed to collect metadata for the management\nof the ATLAS Conditions Database. The structure and implementation of this metadata\nrepository will be described. In addition, we will report its usage since its inception in\nLHC Run1, how it will be exploited in the process of conditions data evolution during\nLS1 (the current LHC long shutdown) in preparation for Run 2, and long term plans to\nincorporate more of its information into future ATLAS Conditions Database tools and\nthe overall ATLAS information infrastructure