David N. Brown Lawrence Berkeley National Lab Representing the BaBar Collaboration The BaBar Mini ...
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Transcript of David N. Brown Lawrence Berkeley National Lab Representing the BaBar Collaboration The BaBar Mini ...
David N. Brown
Lawrence Berkeley National Lab
Representing the BaBar Collaboration
The BaBar Mini
BaBar
BaBar’s Data Formats
Design of the Mini
Mini Performance and Status
The Mini in BaBar’s New Computing Model
David N. Brown LBNL BaBar 2 CHEP03 25 March, 2003
BaBar
5-layer Si Vertex tracker40-layer Drift ChamberDIRC Cherenkov CounterCsI Crystal CalorimeterMuon Chambers in Fe
David N. Brown LBNL BaBar 3 CHEP03 25 March, 2003
BaBar Event Data Formats (2001)
1 These formats were not used except by a few experts2 The ESD format was not complete in 2001, supporting only 3 of the 5 Babar subsystems
FormatDesign Size
(Kbytes)Actual Size
(Kbytes)Usage (2001)
Online raw data 25 32 Reconstruction input
Objectivity raw data 25 50 Unused1
Reconstruction output 100 120 Unused1
Event Summary (ESD) 10 7 Unused1 2
Micro 1 3 Physics Analysis
Event Tags 0.1 1 Event Selection
Event Header ? 4 Component navigation
David N. Brown LBNL BaBar 4 CHEP03 25 March, 2003
A Gap in the Formats Raw, Reco, and ESD formats were not useful
Reading any of these required staging many large files Time to read reco is comparable to running reconstruction
A better persistent model was needed: the Mini
Reco
Raw
Reco Track
Kalman Fit
…
DC Hit Si Hit Si Hit
Cluster
digi
Cluster
digi digi digi
Kalman Fit
Reco Track
Kalman Fit
…
DC Hit Si Hit Si Hit
Cluster
digi
Cluster
digi digi digi
Kalman FitESD
ESD+
Reco
Transient Persistent
David N. Brown LBNL BaBar 5 CHEP03 25 March, 2003
Mini Design Goals Support detector studies
Provide low-level detector details to support common tasks calibration, alignment, diagnostics, and algorithm development
Provide Reconstruction Object interfaces Support detailed Physics analysis
Provide access to the full reconstruction resultsEG: track fits using Kaon mass for material effect predictions
Allow users to follow calibration and alignment changes Allow detector-level systematic error checks Support a detailed event display Support the standard BaBar analysis interface
Make it easy to access A disk size of 10KBytes/event or less A readback speed comparable to the Micro Allow customized output to fit specific needs
David N. Brown LBNL BaBar 6 CHEP03 25 March, 2003
Mini Design Directly persist high-level reconstruction objects
Tracks, calorimeter clusters, PID results, …
Indirectly persist lower-level reconstruction objects Track hits, calorimeter crystals, …
Store ‘raw’ detector quantities (where possible) Digitization values, electronic channel id, …
Pack data to detector precision Aggressively filter detector noise Avoid overhead in low-level ‘persistent’ classes
Used fixed-size classes Align all data members No virtual functions in low-level classes
David N. Brown LBNL BaBar 7 CHEP03 25 March, 2003
Mini Persistence
Reco Track
Kalman Fit
…
DC HitSi Hit Si Hit
Cluster
digi
Cluster
digi digi digi
Kalman Fit
Transient
Pack data from low-level classes into compact objects Persist the entire transient tree in one persistent object
References become indices into embedded arrays Every event fully described by 13 persistent objects
Persistent
David N. Brown LBNL BaBar 8 CHEP03 25 March, 2003
Data Packing Digitize floating point values
Eg track fit parameters and covariance matrix Set packing precision at ~1% of detector resolution Use locally flat, globally logarithmic packing algorithm
Packing precision depends on the value being packedSupports histograms without binning artifacts
Bitwise OR small fields into packed data words
Track Impact parameter
Pack into 17 bits
longword alignment
Pack parameter error into remaining 15 bits
David N. Brown LBNL BaBar 9 CHEP03 25 March, 2003
Mini Analysis Interface The BaBar Analysis Framework is entrenched
Huge investment in Physicist code after 3 years of operation
The original design supported multiple data formats But it had evolved to depend on details of the Micro Providing Mini-compatibility was a major effort
Changes in the base classes, new subclasses, …
The BaBar Mini Analysis interface is now working Physics (Micro) objects are built from native Mini objects Fully compatible with existing user code Provides access to most Mini-specific features Performance is comparable to reading the Micro
David N. Brown LBNL BaBar 10 CHEP03 25 March, 2003
Mini Performance Data size (after ootidy + gzip compression)
6.5 Kbytes per generic physics event 10 Kbytes per multi-hadron event (~10 tracks)
Readback speed 20 mSec per generic event (1GHz pentium III Linux)
Readback operation % time
Transient creation + deletion 35
Objectivity data read 1030
Physics object creation 20
Framework overhead 10
Data field unpacking 0.1
David N. Brown LBNL BaBar 11 CHEP03 25 March, 2003
Single Event Display- MiniSingle Event Display- Micro
David N. Brown LBNL BaBar 12 CHEP03 25 March, 2003
Mini Status The Mini was released for production in 2002
All components of BaBar detector representedTrigger, MC truth matching, Particle ID, …
‘2002’ Reprocessing is nearly complete Should finish this week! Will provide the full Mini for BaBar’s full data sample Reco, Raw, and ESD were not written in this processing
A Large savings in cpu, IO, tape, lock traffic, …
Mini data is available at BaBar Tier-A sites The total Mini sample will be ~10 TeraBytes Access is through dynamic staging Small samples can be exported to smaller sites Physicists are starting to use it
David N. Brown LBNL BaBar 13 CHEP03 25 March, 2003
BaBar’s New Computing Model BaBar has recently revised its computing model
Prompted (partly) by the need to integrate the Mini
The Mini will be ported to use RootIO Allows interactive (CINT) access to production output Embedded arrays will be converted to Root columns
Embedded object classes will be directly reused
A Reduced Mini will replace the existing Micro Cluster Mini objects used directly in analysis into New Micro Cluster other objects separately to complete the Mini
The Analysis interface will be re-implemented Optimized for Mini access
David N. Brown LBNL BaBar 14 CHEP03 25 March, 2003
Conclusions BaBar has implemented a new Event format: the Mini
Replaces inefficient Raw, Reco, and ESD formats Provides access to detector detail for average users
The full BaBar data sample will soon be available in Mini format
BaBar is implementing a new Computing Model The Mini will be ported to RootIO The Micro will be replaced with a Reduced Mini The Analysis interface will be re-implemented The new model will be deployed in late 2003
We are close to achieving our original goal of a flexible, unified, efficient event data format