Abstract
During the 2013-2014 shutdown of the Large Hadron Collider, ATLAS switched to a new event data model for analysis, called the xAOD. A key feature of this model is the separation of the object data from the objects themselves (the ‘auxiliary store’). Rather than being stored as member variables of the analysis classes, all object data are stored separately, as vectors of simple values. Thus, the data are stored in a ‘structure of arrays’ format, while the user still can access it as an ‘array of structures’. This organization allows for on-demand partial reading of objects, the selective removal of object properties, and the addition of arbitrary user- defined properties in a uniform manner. It also improves performance by increasing the locality of memory references in typical analysis code. The resulting data structures can be written to ROOT files with data properties represented as simple ROOT tree branches. This paper focuses on the design and implementation of the auxiliary store and its interaction with ROOT.
Highlights
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The first data-taking run (Run 1) of the ATLAS experiment [1] was very successful
ATLAS converted on output the complex transient data model to a simpler persistent data model which could be written to ROOT directly
Summary
This content has been downloaded from IOPscience. Ser. 664 072045 (http://iopscience.iop.org/1742-6596/664/7/072045) View the table of contents for this issue, or go to the journal homepage for more. Download details: IP Address: 137.138.124.206 This content was downloaded on 24/02/2016 at 13:50 Please note that terms and conditions apply. 21st International Conference on Computing in High Energy and Nuclear Physics (CHEP2015) IOP Publishing. Journal of Physics: Conference Series 664 (2015) 072045 doi:10.1088/1742-6596/664/7/072045. University of Glasgow, Department of Physics and Astronomy, Glasgow G12 8QQ, United Kingdom 2 CERN, CH-1211 Geneva 23, Switzerland 3 Albert-Ludwigs-Universitat, Fakultat fur Mathematik und Physik, Hermann-Herder Str. 3, D-79104 Freiburg i.Br., Germany 4 University of Massachusetts, Department of Physics, 710 North Pleasant Street, Amherst, MA 01003, USA 5 Brookhaven National Laboratory, Physics Department, Bldg. 510A, Upton NY 11973, USA 6 Argonne National Laboratory, High Energy Physics Division, 9700 S.
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