Prompt reconstruction of LHC collision data with the ATLAS reconstruction software

Since the start of LHC operations in November 2009, the ATLAS detector has recorded many millions of collision events. With the luminosity increasing rapidly in 2010, it is a challenge for the reconstruction and data distribution efforts to provide physics-quality data to analysts around the world within a short timescale. In this note I will describe how a two-pass system, where calibration constants and corrections are calculated on a subset of the data before being used in bulk reconstruction, provides a robust and well-monitored mechanism for meeting these challenges.