HBase / Phoenix-based Data Collection and Storage for the ATLAS EventIndex

The ATLAS EventIndex is the global catalogue of all ATLAS real and simulated events. During the LHC long shutdown between Run 2 (2015-2018) and Run 3 (2022-2025) its components were substantially revised, and a new system has been deployed for the start of Run 3 in Spring 2022. The new core storage system is based on HBase tables with a Phoenix interface. It allows faster data ingestion rates and scales better than the old system. This paper describes the data collection, the technical design of the core storage, and the properties that make it performant: The compact and optimized design of the events table, which already holds more than 400 billion entries, and all the auxiliary tables; The EventIndex Supervisor, in charge of orchestrating the whole data collection, has been simplified thanks to the loaders, the Spark jobs that load the data into the new core system. The extractors, in charge of preparing the pieces of data that the loaders will put into the final back-end, have been updated too. The data migration from HDFS to HBase and Phoenix is also described.