Computing for Alice at GSI (Proposal) (Marian Ivanov)

Outline ● Priorities ● Assumptions ● Proposal – GSI Tier2 - special role – Focus on the calibration and alignment - TPC and TRD

Priorities ( ) ● Detector calibration and alignment (TPC-ITS- TRD) – First test – Cosmic and Laser – October 2007 – To be ready for first pp collision ● First paper – Time scale - Depends on success of October tests – Goal : ~ 1 week (statistic about 10^4-10^5 events) ● ==> The calibration and alignment has the TOP priority ( )

Assumptions ● CPU requirements – Relative ● Simulation ~ 400 a.u ● Reconstruction ~ 100 a.u ● Alignment ~ 1 a.u ● Calibration ~ 1 a.u ● To verify and improve the calibration and alignment several passes through data are necessary ● The time scale for one iteration ~ minutes, hours ==> ● The calibration and alignment algorithms should be decoupled from the simulation and reconstruction ● The reconstruction algorithm should be repeated after retuning of the calibration

Assumptions – Data volume to process - accessibility ● pp event ● ESD size ~ 0.03 Mby/ev ● ESDfriend ~ 0.45 Mby/ev ● (0.5 Tby-5 TBy) per 10^6 events - (no overlaps – 10 overlapped events) ● ESD (friends) Raw data (zero suppressed) – Local ~ 10^5-10^6 pp - 10^4 pp – Batch ~ 10^6-10^7 pp - 10^5 pp – Proof ~ 10^6-10^7 pp - – Grid >10^7 pp - 10^6 pp

Assumptions ● Type of analysis (requirements) ● First priority – Calibration of TPC – 10 ^4 -10^5 pp – Validation of the reconstruction - 10^4-10^5 pp – Alignment TPC, TPC-ITS – 10^5 pp + 10^4-10^5 cosmic

Assumptions ● Alien and PROOF are in the test phases ● Improvement in time, but, still fragile ● Difficult to distinguish between software bugs in analysis, calibration code and Alien and PROOF internal problems ● Chaotic (user) analysis -> can lead to chaos ● Not existing quotas, priorities ● Some restrictions already implemented ● e.g. On ALIEN - Possibility to submit jobs only for staged files ● Requirements for staging files – officially defined by PWGX ● The requirements from Detectors ?

Assumptions ● Alice test in October – (in one month) ● Full stress test of system ● Significant data volume ● ~20 Tby of raw data from test of 2 sectors (2006) ● Bottleneck (2006) – The processing time given by time of the data access - CPU time negligible ● We should be prepared for different scenarios ● We would like to start with the data copied at GSI and reconstruct/calibrate/align locally, later switch to GRID (The same we did in 2006) ● This approach enables several fast iteration over data

Proposal ● Algorithmic part of our analysis, calibration software should be independent of the running environment – TPC calibration classes (components) as example (running, tuning OFFLINE, used in HLT, DAQ and Offline) ● Analysis and calibration code should be written following a component based model – Tselector (for PROOF) and AliAnalysisTask (at GRID/ALIEN) – just simple wrapper

Example - Component ● Component: – class AliTPCcalibTracks : public TNamed {..... ● public :.. ● virtual void ProofSlaveBegin(TList * output); ● virtual void ProcessTrack(AliTPCseed * seed); ● void Merge(TCollection *); ● // histograms, Fitters.... ● Selector - wrapper – class AliTPCSelectorTracks : public TSelector {.... ● AliTPCcalibTracks *fCalibTracks; //! calib Tracks object – } – Bool_t AliTPCSelectorTracks::Process(Long64_t entry) ● fCalibTracks->ProcessTrack(seed); ●

Software development ● Write component ● Software validation - Sequence: 1)Local environment (first filter) 1)Stability – debugger 2)Memory consumption – valgrind, memstat (root) 3)CPU profiling - callgrind, vtune 4)Output – rough, quantitative – if possible 2)Batch system (second filter) 1)Memory consumption – valgrind, memstat 2)CPU profiling 3)Output - better statistic 3)PROOF 1)For rapid development – fast user feedback 2)Iterative improvement of algorithms, selection criterias... 3)Improve statistic 4)Be ready for GRID/ALIEN 1)Improve statistic

What should be done ● Test data transfer to GSI ( ~TBytes) – Using Alien – Kilian – Using xrdcp ● File system toolkit on top of xrd to be developed ● Write components ● Test and use of PROOF at GSI

Conclusion ● An analysis/calibration schema has been proposed ● It is not harder to implement than a regular TSelector/AliTask... ● TPC calibration has already been partly implemented using proposed schema ● This schema allows much better testing of the code before proceeding to the next steps (Local ->Batch/Proof-> GRID) ● As the same components are used in each step, we are not blocked if one of the distributed systems doesn't work properly