Abstract
ATLAS developed and employed for Run 1 of the Large Hadron Collider a sophisticated infrastructure for metadata handling in event processing jobs. This infrastructure profits from a rich feature set provided by the ATLAS execution control framework, including standardized interfaces and invocation mechanisms for tools and services, segregation of transient data stores with concomitant object lifetime management, and mechanisms for handling occurrences asynchronous to the control framework's state machine transitions. This metadata infrastructure is evolving and being extended for Run 2 to allow its use and reuse in downstream physics analyses, analyses that may or may not utilize the ATLAS control framework. At the same time, multiprocessing versions of the control framework and the requirements of future multithreaded frameworks are leading to redesign of components that use an incident-handling approach to asynchrony. The increased use of scatter-gather architectures, both local and distributed, requires further enhancement of metadata infrastructure in order to ensure semantic coherence and robust bookkeeping. This paper describes the evolution of ATLAS metadata infrastructure for Run 2 and beyond, including the transition to dual-use tools—tools that can operate inside or outside the ATLAS control framework—and the implications thereof. It further examines how the design of this infrastructure is changing to accommodate the requirements of future frameworks and emerging event processing architectures.
Highlights
Evolution of event processing frameworks and the need for metadata access in analyses downstream of experiments’ frameworks, require concomitant evolution of metadata handling and its supporting infrastructure. This presentation describes some of the ways in which ATLAS metadata infrastructure is evolving to address these needs
– There are certain metadata that identify the file and its contents and how it connects to larger data groupings such as datasets
– Due to potential blocking and other issues in multithreaded deployment – Framework retains as necessary for some purposes the notion of “schedulable incidents,” but proposes that most operations be done under the control of a scheduler – “Asynchronous to Gaudi state machine transitions” is not the same as “unschedulable”
Summary
Metadata handling and metadata flow, though, differ in significant ways from event loop management and execution control. – Handling may be asynchronous to control framework state machine transitions, object lifetime management is different, scheduling, processing, and propagation may be different,. – Job-configuration depends on data that is stored as in-file metadata This can include cached conditions data using an interval-of-validity structure. – At the analysis level the metadata can be used to help physicists avoid database or release accesses by caching data needed within the file. At this point the data and tools need to be in a form that can be used outside Athena, the ATLAS control framework. – MataDataSvc and MetaDataTools are invoked via handling FileIncidents, that are fired on file boundaries
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