1. COMPASS off-line computing
the COMPASS experiment
the analysis model
the off-line system
hardware
software
CHEP2000

2. The COMPASS Experiment (Common Muon and Proton Apparatus for Structure and Spectroscopy)
Fixed target experiment at the CERN SPS
approved in February 1997
commissioning from May 2000
data taking for at least 5 years
collaboration
about 200 physicists from Europe and Japan
diversified physics programme
muon beam
gluon contribution to nucleon spin, quark spin distribution functions
hadron beam
glueballs, charmed baryons, Primakoff reactions
all measurements require high statistics
CHEP2000

3. Experimental Apparatus
Two stage spectrometer (LAS, SAS)
Several new detectors
GEMs, microMega, straw trackers, scintillating fibers, RICH,
and silicon detectors, Calorimeters, Drift and MWP Chambers
(440 K electronic channels)
Not an easy geometry
highly inhomogeneous magnetic field (SM1, PTM)
CHEP2000

4. Expected Rates beam intensity: 108 muons/s with duty cycle of 2.4s/14s
RAW event size: ~ kB
trigger rate: 104 events/spill
DAQ designed for 105 events/spill (hadron programme)
on-line filtering
continuous data acquisition flux: 35 MB/s
data taking period ~100 days/year:
~ 1010 events/year, ~ 300 TB/year of RAW data
CHEP2000

5. COMPASS analysis model
The RAW data
will be stored at CERN (no copy foreseen) and
have to be accessible during all the experiment lifetime
will be processed at CERN,
in parallel to and at the same speed of data acquisition
assuming
no pre-processing for calibrations
~ 1 reprocessing of the full data set
processing time 2 SPECint95-sec/event
calibrations “on-line”, powerful on- off-line monitoring, small data subset reprocessing if fast raw data access
the needed CPU power is 2000 SpecInt95 (~ CU)
Physics analysis will be performed at the home institutes,
as well as specific studies and MC production
the relevant sets of data must have a much smaller size remote and concurrent access to raw data important (“PANDA” model…)
CHEP2000

6. General choices In 1997 COMPASS decided to
build a completely new software system
use OO techniques
C++ as programming language
ODB to store the data.
Given the
short time scale, the ‘small’ collaboration,
the novelty, and the well known difficulty of the tasks,
it was mandatory to
collaborate with the IT division
foresee the use LHC++ and commercial products (HepODBMS, Objectivity/DB)
look at other developments (ROOT)
CHEP2000

7. Off-line system Hardware Software central data recording
COMPASS Computing Farm (CCF)
(see M. Lamanna presentation, Feb. 7, session E)
Software
Data structures and access
CORAL (Compass Reconstruction and AnaLysis) program
CHEP2000

8. Central data recording (CDR)
updated version of the CERN Central Data Recording (CDR) scheme
the on-line system
performs the event building (and filtering) - ALICE DATE system
writes RAW data on local disks
files in byte-stream format (10-20 parallel streams),
keeping a "run" structure (typical sizes of 50 GB)
the Central Data Recording system
transfers the files to the COMPASS Computing Farm, at the computer center (rate of 35 MB/s)
the COMPASS Computing Farm CCF
formats the data into a federated database (Objectivity/DB)
converts the RAW events in simple persistent objects
performs fast event tagging or clusterisation (if necessary)
sends the DB to HMS for storage
CHEP2000

9. COMPASS Computing Farm (CCF)
Beginning 1998:
IT/PDP Task Force: computing farms for high-rate experiments (NA48, NA45, and COMPASS).
Proposed model for the CCF: hybrid farm with
about 10 Proprietary Unix servers (“data servers”)
about 200 PCs (”CPU clients”), 2000 SPECint95 (0.2 s/ev)
3 to 10 TB of disk space
Present model: farm with
PCs as “data servers” and ”CPU clients”
order of 100 dual PIII machines
standard PCs running CERN certified Linux (now: RH5.1 with kernel /12)
CHEP2000

10. CCF
CHEP2000

11. COMPASS Computing Farm (cont.)
The data servers will
handle the network traffic from the CDR,
format the RAW events into a federated DB , and send them to the HSM
and
receive the data to be processed from the HSM, if needed,
distribute the RAW events to the PCs for reconstruction
receive back the output (persistent objects), and send it to the HSM.
The CPU clients will
process the RAW events (reconstruction of different runs/files has to run in parallel)
a real challenge:1000 ev/sec to be stored and processed by 100 dual PCs
tests with prototypes are going on since two years; good results
CHEP2000

12. Off-line system Software Data structures
Event DB
Experimental conditions DB
Reconstruction quality control monitoring DB
MC data
CORAL: Compass Reconstruction and AnaLysis program
CHEP2000

13. Data structures Event DB
event headers containers: small dimensions (on disk), basic information like tag, time,...
RAW event containers: just one object with event (DATE) buffer 
reconstructed data containers: objects for physics analysis
direct access to objects
run: file structure not visible
association to avoid duplications
direct: raw - reco. data
via “time”: raw - mon. ev
CHEP2000

14. Data structures (cont.)
Experimental conditions DB
includes all information for processing and physics analysis
(on-line calibrations, geometrical description of the apparatus...)
based on CERN porting of BABAR Condition Database package (included in HepODBMS)
versioning of  objects
access to valid information using event time
Reconstruction quality control monitoring data
includes all quantities needed for monitoring the stability of the reconstruction and of the apparatus performances
stored in Objectivity/DB
Monte Carlo data
we are using Geant3 (Geant4: under investigation, not in the short term)
ntuples, Zebra banks
CHEP2000

15. status Event DB Experimental conditions DB
version 1 ready
Experimental conditions DB
in progress: implementation started
Reconstruction quality control monitoring data
starting
Monte Carlo data
ready
CHEP2000

16. CORAL COmpass Reconstruction and AnaLysis program
fully written in C++, OO technique
modular architecture with
a framework providing all basic functionalities
well defined interfaces for all components needed for event reconstruction
insulation layers for
all "external" packages
access to the experimental conditions and event DB (reading and writing persistent objects) - HepODBMS
to assure flexibility in changing both reconstruction components and external packages
components for event reconstruction
developed in parallel
detector decoding, pattern rec. in geom. regions, track fit, RICH and Calorimeter rec., …
CHEP2000

17. CORAL
CHEP2000

18. CORAL status development and tests on Linux
we try to keep portability on other platforms (Solaris)
framework: almost ready work going on to interface new reconstruction components and access to experimental conditions DB
reconstruction components:
integrated inside CORAL and tested MC event reading and decoding, track pattern recognition, track fit,…
integration foreseen soon RICH pattern recognition, Calorimeter reconstruction, vertex fit,...
under development detector (DATE buffer) decoding, in parallel with on-line,...
Goal: version 1 ready at the end of April 2000
all basic functionalities, even if not optimised
as for all other off-line system components
CHEP2000

19. General comments
most of the problems we had are related to the fact that we are still
in a transition period:
no stable environment
both for available software (LHC++) and OS (Linux)
lack of standard “HEP made” tools and packages
commercial products seem not to be always a solution
too few examples of HEP software systems using new techniques
expertise and resources
having a large number of physicists knowing the new programming
language (and techniques) requires time
all the work has been done by a very small enthusiastic team
(3 to 10 fte in 2 years)
Still, we think we made the right choice
CHEP2000

20. “FOCUS …. recognises the role that the experiment has
from the minutes of the 16th meeting of FOCUS
held on December 2, 1999:
“FOCUS …. recognises the role that the experiment has
as a "test-bed" for the LHC experiments.”
CHEP2000

21. CHEP2000