Advancements in the in-file metadata system for the ATLAS experiment

The High-Luminosity upgrade of the Large Hadron Collider (HL-LHC) will increase luminosity and the number of events by an order of magnitude, demanding more concurrent data processing. Event processing is trivially parallel, but metadata handling is more complex and breaks that parallelism. However, correct and reliable in-file metadata is crucial for all workflows of the experiment, enabling tasks such as job configuration, decoding trigger information, and keeping track of event selection. Therefore, ATLAS is enhancing its current in-file metadata system to support metadata creation and propagation in more robust ways. This work presents developments in the evolution of the metadata system. We investigate storage technologies tailored for infile metadata payload, exploring advancements in the ROOT framework, which is used for storing data collected by the ATLAS experiment. We also discuss the challenging process of summarising the content of metadata objects when combining information from several sources.