Tier-1 and Tier-2 real-time analysis experience in CMS Data Challenge 2004

During the CMS Data Challenge 2004 a real-time analysis was attempted at INFN and PIC Tier-1 and Tier-2s in order to test the ability of the instrumented methods to quickly process the data. Several agents and automatic procedures were implemented to perform the analysis at the Tier-1/2 synchronously with the data transfer from Tier-0 at CERN. The system was implemented in the LCG-2 Grid environment and allowed on-the-fly job preparation and subsequent submission to the Resource Broker as new data came along. Running job accessed data from the Storage Elements via remote file protocol, whenever possible, or copying them locally with replica manager commands. Details of the procedures adopted to run the analysis jobs and the expected results are described. An evaluation of the ability of the system to maintain an analysis rate at Tier-1 and Tier-2 comparable with the data transfer rate is also presented. The results on the analysis timeline, the statistics of submitted jobs, the overall efficiency of the GRID services and the overhead introduced by the agents/procedures are reported. Performances and possible bottlenecks of the whole procedure are discussed.