The story of BaBar: an IT perspective Roger Barlow DESY 4 th September 2002

Roger Barlow 4 Sept 2002BaBar: an IT perspective Slide 2/18 Example:             OPAL BaBar (Work in progress)

Roger Barlow 4 Sept 2002BaBar: an IT perspective Slide 3/18 History 1995TDRC First data 0.5 fb -1 Objectivity / kanga 2000 First results 23 fb -1 File transfer 2001 Sin 2  0.59  0.14  fb -1 Tier A sites 2002 Sin 2    fb -1 Grid

Roger Barlow 4 Sept 2002BaBar: an IT perspective Slide 4/18 Datataking: “Drinking from a firehose” L1 TriggerL3 Trigger OPR farm Data store 200 kB/evt Hz 4.2 ns 1-2kHz PowerPCs in VME crates 200+ CPUs 32 SUN U5

Roger Barlow 4 Sept 2002BaBar: an IT perspective Slide 5/18 C++ “Unorthodox but very nice introduction to programming” Amazon.com review Decision taken: approved languages C++ and F90 (Nobody used F90) HEP escapes at last from FORTRAN! Other experiments follow Software immediately becomes VERY object-oriented

Roger Barlow 4 Sept 2002BaBar: an IT perspective Slide 6/18 C++ in practice Design Old New Abstract objects EmcCluster:AbsRecoCalo AbsRecoCalo: AbsEvtObj EmcClusterMoments: EmcAbsClusterProperty EmcClusterDistance: EmcAbsClusterProperty The software was written on time and it worked.

Roger Barlow 4 Sept 2002BaBar: an IT perspective Slide 7/18 Some lessons RogueWave Commercial class library Built in to software from start Superseded by STL, CLHEP Licence arrangements restrictive/expensive Now (painfully) removed Calibration System impressive technically Can’t do what you want it to Event Display Powerful system (‘Event display server’) written by experts Unwieldy and unreliable for non- experts away from SLAC Little used

Roger Barlow 4 Sept 2002BaBar: an IT perspective Slide 8/18 Objectivity ‘Persistent data’ Objects still present when a job is run again- stored on disc Need to handle pointers Need to match data on disk to objects the program knows about Need to do this fast and furiously Objectivity does this – no alternative Performance issues in OPR: solved (hard work+vendor co- operation) Performance issues in analysis: not satisfactory (physicists more random)  KANGA Long-term viability?

Roger Barlow 4 Sept 2002BaBar: an IT perspective Slide 9/18 Success: the penalty PEPII delivers and BaBar can handle it Design Luminosity achieved Now Heading for BaBar efficiency ~ 95% (This is a race. KEK and Belle are close behind!) Data handling Need to provide Disk (or tape) for data storage Machines for OPR Machines for analysis Moore’s Law is not strong enough Need new computing model Central  Distributed

Roger Barlow 4 Sept 2002BaBar: an IT perspective Slide 10/18 File Transfer Data transfer From SLAC to outside sites Large (RAL, IN2P3) and small (university) Use network transfer rather than shipping tapes ESNET in US, JANET+ GEANT in Europe Use RAL, Rome, etc as staging posts File copy programs bbcp and bbftp developed, now standard Copy with multiple streams Achieve Mbit/s Data available within days Chasing improvement continuous task

Roger Barlow 4 Sept 2002BaBar: an IT perspective Slide 11/18 Spreading the load Serious computing power at outside institutes Each UK BaBar group ~1TB fast disc (1998) Compute farm (80 CPU) (2000) Used for analysis Used for MC simulation

Roger Barlow 4 Sept 2002BaBar: an IT perspective Slide 12/18 RAL Tier A Centre UK GRID Funds available Tier 1/A centre at RAL 200+ CPUs 35 TB disk this year (increasing as price drops) Rebate on common fund contribution Everybody happy Similar centres at IN2P3, Bologna, plus Karlsruhe in future

Roger Barlow 4 Sept 2002BaBar: an IT perspective Slide 13/18 Future Development Many users running jobs on distributed data with distributed CPUs Don’t want technical detail GRID provides the answer User specifies data description and job Grid tools locate files, find CPUs, submit jobs BaBar today: LHC tomorrow MC:RB

Roger Barlow 4 Sept 2002BaBar: an IT perspective Slide 14/18 Authentication Uses RSA encryption to prove to other computers (‘gatekeepers’) that you are who you say you are Certificate Authorities Certificates issued by trusted organisations to people they know and trust (or people they trust know and trust) Establish mutual trust within BaBar for UKHEP,CNRS, etc But authentication is not authorisation! Grid Certificate

Roger Barlow 4 Sept 2002BaBar: an IT perspective Slide 15/18 Authorisation Users with Grid certificates authorised to use resources at all BaBarGrid sites Getting on this list is made easy (for BaBar users with a Grid certificate ) Dynamic account pool avoids need for 500x50 userids SLACMANCHESTERBaBarGrid sites Grid Certifica te BaBar VO list cron job gridmap files

Roger Barlow 4 Sept 2002BaBar: an IT perspective Slide 16/18 The BaBar VO

Roger Barlow 4 Sept 2002BaBar: an IT perspective Slide 17/18 The BaBar Grid Demonstrator Rudimentary Grid submission and retrieval Full features to be added later

Roger Barlow 4 Sept 2002BaBar: an IT perspective Slide 18/18 The Future: Some Possibilities SRB as universal file system Extend VO system for authorisation Desk-to-desk Video conferencing More Compute and Storage farms Metadata specification using xml Join EDG testbed rollout Framework VI