Just-in-time workflow management for DUNE

We describe the justIN workflow management system developed by DUNE to address its unique requirements and constraints. The DUNE experiment will start running in 2029, recording 30 PB/year of raw data from the detectors, with typical readouts at the scale of gigabytes, but with regular supernova candidate readouts of several hundred terabytes. DUNE benefits from the rich heritage of neutrino experiments at Fermilab, including the use of the SAM system to manage data, metadata, and processing campaigns. Due to the increase in scale required for DUNE, SAM’s metadata database has been replaced by a new system, MetaCat, and its data management role is now taken up by Rucio. A new workflow system, justIN, has been developed since 2021 to replace the remaining functionality of SAM, and to tie together MetaCat, Rucio, and the GlideInWMS job management system to allow data processing campaigns involving hundreds of thousands of files and jobs using CPU and storage on four continents. Crucial to the design of justIN is an evolution of SAM’s just-in-time philosophy, in which running jobs ask the central service for the optimal file to process next given their location. This model and the SAM interface are directly supported by the liquid argon data processing application used by DUNE, and justIN’s design allows us to continue to support both. justIN goes a step further by assigning the workflows themselves to running GlideInWMS pilot jobs based on the locations of unprocessed files in active workflows at that time. This architecture allows the system to rapidly respond to problems such as downtimes, and to the sudden appearance of higher priority tasks such as processing supernova candidates.