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OADB and large shared files

The Offline Analysis Database (OADB) is a repository of relatively large configuration/calibration files that are used by the analysis framework, containing for example the 'TPC splines' with the parametrised dE/dx response of the TPC and calibration files for event plane calculation. The data are generally stored in ROOT files, and the primary repository is on the CERN EOS file system, which is accessible from lxplus:

/eos/experiment/alice/analysis-data

We have preserved the same directory structure found on AliPhysics, and the same permissions: for instance, PWGLF is writable by all members of alice-svn-pwglf (whose members can be edited by the group conveners).

Using the OADB on the grid

Every day, in concomitance with the AliPhysics daily tag (at 4pm Geneva time), this folder is snapshotted on CVMFS under the following path:

/cvmfs/alice.cern.ch/data/analysis/YYYY/vAN-YYYYMMDD

carrying the same name as the corresponding AliPhysics tag. Moreover, at every AliRoot/AliPhysics production release, we also snapshot at:

/cvmfs/alice.cern.ch/data/prod/v5-XX-YY-01

where the last component is the AliPhysics tag name.

CVMFS brings the advantage to make data access from Grid jobs reliable and faster due to caching (files unchanged in two different snapshots are not downloaded twice).

Using the OADB on your local system

If your system is connected to the network, you can access the OADB via (x)rootd, but setting the ALICE_DATA environment variable

export ALICE_DATA=root://eospublic.cern.ch//eos/experiment/alice/analysis-data

If you want to have your OADB data locally, you can download it from lxplus:

export OADB_PATH=/path/to/my/local/oadb
rsync -av --delete cern_user@lxplus.cern.ch:/eos/experiment/alice/analysis-data/ $OADB_PATH/

Trailing slashes are important to rsync! Do not forget them!

Note that the variable $OADB_PATH must be exported to the environment where you run your local analysis in order to make it visible to the job.

Accessing the OADB from code

In order to profit from the separate storage for large files we have created an interface in AliRoot to allow transparent access to OADB files using a relative path. For instance, if you want to access the following large OADB data file:

PWGLF/FORWARD/CORRECTIONS/data/fmd_corrections.root

you can do:

TFile::Open(AliDataFile::GetFileNameOADB("PWGLF/FORWARD/CORRECTIONS/data/fmd_corrections.root"))

The static function AliDataFile::GetFileNameOADB returns the first accessible full URL of the OADB file by finding the first match from the following ordered list of paths:

  1. $OADB_PATH/<file>
  2. $ALICE_DATA/OADB/<file>
  3. $ALICE_PHYSICS/OADB/<file>
  4. /cvmfs/alice.cern.ch/data/prod/v5-XX-YY-01/OADB/<file> (for Grid jobs, or with CVMFS installed)
  5. /cvmfs/alice.cern.ch/data/analysis/YYYY/vAN-YYYYMMDD/OADB/<file> (for Grid jobs, or with CVMFS installed)
  6. root://eospublic.cern.ch//eos/experiment/alice/analysis-data/OADB/<file>

This means that for laptop analysis it will always be possible to access data files, somehow, and in a transparent fashion.

Non-OADB data files

The same EOS path has also PWG-specific directories, outside the OADB one, for other analysis-specific data. The following interface can be used to access files from there:

TFile::Open(AliDataFile::GetFileName("PWGMM/my_large_data.root"))

Note the difference between GetFileName() and GetFileNameOADB().

In this case, the file will be searched in the following locations in order:

  1. $ALICE_DATA/<file>
  2. $ALICE_PHYSICS/<file>
  3. /cvmfs/alice.cern.ch/data/prod/v5-XX-YY-01/<file> (for Grid jobs, or with CVMFS installed)
  4. /cvmfs/alice.cern.ch/data/analysis/YYYY/vAN-YYYYMMDD/<file> (for Grid jobs, or with CVMFS installed)