Implementation of the ATLAS Run 2 event data model

[摘要] 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.

[发布机构] University of Glasgow, Department of Physics and Astronomy, Glasgow; G12 8QQ, United Kingdom^1;CERN, Geneva 23; CH-1211, Switzerland^2;Albert-Ludwigs-Universität, Fakultät für Mathematik und Physik, Hermann-Herder Str. 3, Freiburg i.Br.; D-79104, Germany^3;University of Massachusetts, Department of Physics, 710 North Pleasant Street, Amherst; MA; 01003, United States^4;Brookhaven National Laboratory, Physics Department, Bldg. 510A, Upton; NY; 11973, United States^5;Argonne National Laboratory, High Energy Physics Division, 9700 S. Cass Avenue, Argonne; IL; 60439, United States^6

[效力级别] 计算机科学 [学科分类] 计算机科学（综合）

[关键词] Data properties;Design and implementations;Large Hadron Collider;Memory references;Object property;Selective removal;Structure of array;Tree branches