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Efficient Data Handling Techniques for Event Processing in LHCb Experiments

Explore key concepts like accessing event data, working with containers, understanding data stores, and conventions for data access in GaudiAlgorithm. Learn about object storage, persistence, and access methodologies used in the LHCb experiments.

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Efficient Data Handling Techniques for Event Processing in LHCb Experiments

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  1. Accessing Event Data

  2. Event Data Reside In Data Store • Tree - similar to file system • Identification by path”/Event/MC/Particles”LHCb::MCParticleLocation::Default • Objects or • Containers of objectsKeyedContainer<Type>

  3. Containers: e.g. KeyedContainer • Templated class • Usually hidden to end-user code by typedefs in header file • Iteration like any STL vector • //note LHCb:: namespace • LHCb::MCParticle::Container* parts = … ; • LHCb::MCParticle::Container::const_iterator i;for( i=parts->begin(); i != parts->end(); i++ ) • { info() << (*i)->particleID().pid() << endmsg;}

  4. Data Service Algorithm (3) Request load (1) get<class>(location) PersistencyService Request dispatcherSICB, ROOT,.. (5) Register Conversion Service (4) Request creation Converter Converter Converter Converter Understanding Data Stores: Loading Unsuccessful ifrequested object is not present (2) Search in Store Try to accessan object data Data Store

  5. Caveats • Consider Objects on the store asREAD-ONLY • Do not modify existing objects! • Do not destroy existing objects! • Never, never delete an object which is registered to the store • It’s not yours! • It will only screw up others!

  6. Data Access In GaudiAlgorithm • const LHCb::MCHeader* evt = • get<LHCb::MCHeader>( LHCb::MCHeaderLocation::Default ); • // No need to test a return code, this method throws • // an exception if data is not found

  7. Conventions • For Event Model objects of type TYPE: • The actual type stored in TES • LHCb::<TYPE>::Container • Vector of pointers [ std::vector<TYPE*> ] • LHCb::<TYPE>::Vector • Vector of “pointers-to-const” [ std::vector<const TYPE*> ] • LHCb::<TYPE>::ConstVector • “default” location in TES : • LHCb::<TYPE>Location::Default

  8. Specify Event Data Input EventSelector.Input = { “DATAFILE=‘a_filename’ [Spec]” [,“DATAFILE=‘another_filename’ [Spec]”] }; • Event data input is specified in the job options • [Spec] is an array of qualified strings:KEY1=‘VALUE1’ … KEYn=‘VALUEn’ • Several files can be specified, separated by a comma

  9. Specify POOL Event Input • EventSelector.Input = {"DATAFILE='PFN:castor:/castor/cern.ch/grid/lhcb/production/DC06/v1-lumi2/00001284/SIM/00001284_00000001_1.sim' TYP='POOL_ROOTTREE' OPT='READ'"} • PFN: keyword tells POOL this is a physical file name • castor: keyword selects data transfer protocol (rootd in this case)omit for a disk file • OPT=‘READ’ is read only file

  10. Specify POOL Event Input • For simple file on disk • EventSelector.Input ={ • "DATAFILE=‘/software/lhcb/BenderData/Bs2PsiPhi/00001395_00000005_5.dst' TYP='POOL_ROOTTREE' OPT='READ'"}

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