The ALICE Run 3 Online / Offline Processing
David Rohr (for the ALICE Collaboration)

TL;DR
The paper describes the ALICE Run 3 upgrade, introducing a unified online/offline data processing framework called O2, capable of handling 50 times more data with real-time reconstruction and calibration.
Contribution
It presents a new integrated computing scheme for high-rate data processing in particle physics experiments, combining online and offline workflows in a unified system.
Findings
Real-time processing of 50 kHz Pb--Pb collision data.
Unified online/offline framework (O2) replaces separate systems.
Capable of handling peak data rates for Run 3.
Abstract
The ALICE experiment has undergone a major upgrade for LHC Run 3 and will collect data at an interaction rate 50 times larger than before. The new computing scheme for Run 3 replaces the traditionally separate online and offline frameworks by a unified one, which is called O2. Processing will happen in two phases. During data taking, a synchronous processing phase performs data compression, calibration, and quality control on the online computing farm. The output is stored on an onsite disk buffer. When there is no beam in the LHC, the same computing farm is used for the asynchronous reprocessing of the data which yields the final reconstruction output. The O2 project consists of three main parts:. The Event Processing Nodes (EPN) equipped with GPUs deliver the bulk of the computing capacity and perform the majority of the reconstruction and the calibration. The First Level Processors…
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