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GeezerVison is showing github.com — Share the scaled TPC distortions between digitizers through a file by sawenzel · Pull Request #16091 · AliceO2Group/AliceO2

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@sawenzel

@sawenzel sawenzel commented Nov 9, 2026 •
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This PR adds the option --tpc-distortion-file to the TPC digitizer, so that the distortions scaled to the instantaneous luminosity are computed only once per job.

With distortion type 2, every digitizer lane recalculates the scaled distortions from the CCDB maps in every timeframe. In Pb-Pb this takes about 3 minutes of CPU per lane and timeframe and, together with the correction maps it needs, more than 1 GB of memory per lane.

With the option, the first digitizer computes the scaled distortions and writes them to the file; the other lanes and the later timeframes of the job read it in under a second. The file is keyed on the ETags of the two CCDB maps, TPCCorrMap.lumiInst and the mean-luminosity overrides, and a lock file makes sure that only one process computes. In addition, the correction maps are now released after the recalculation, since only the distortions are used for the digitization.

The effect for one Pb-Pb timeframe (run 572106) with 8 lanes:

peak PSS wall time
before 15.1 GiB 216 s
corrections released, no file 11.9 GiB 221 s
with file, first timeframe (computed with 8 threads) 11.0 GiB 77 s
with file, later timeframes 10.8 GiB 48 s

Note that the digits do not change: with and without the file they are identical to those of the current digitizer, and without the option the only change is the released correction maps. The use in O2DPG is prepared in AliceO2Group/O2DPG#2541, and the multithreaded digitizer of #16090 will use the same file once both are merged.

https://its.cern.ch/jira/browse/O2-7309

Assisted by Claude Code.

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sawenzel and others added 2 commits November 9, 2026 16:50
@sawenzel @claude
Release the TPC distortion corrections after the recalculation
e070a1f 
This frees memory in the TPC digitizer that is not needed after the recalculation of the scaled distortions.

- The digitizer only uses the global distortions of the main map.
- The global corrections of the main and the derivative map are now released after the recalculation.

https://its.cern.ch/jira/browse/O2-7309

Co-Authored-By: Claude Opus 5.5 <[email protected]>
@sawenzel @claude
Share the scaled TPC distortions between digitizers through a file
ce4daee 
This adds the option --tpc-distortion-file to the TPC digitizer, so that the scaled distortions of a job are computed only once.

- The first digitizer computes the scaled distortions and writes them to the file.
- The other lanes and later timeframes read the file instead of recomputing.
- The file is keyed on the ETags of the CCDB maps, TPCCorrMap.lumiInst and the mean-luminosity overrides.
- A file written for other inputs is replaced.
- A lock file serialises the digitizers of different processes.
- Without a usable lock or ETag the distortions are computed as before.

https://its.cern.ch/jira/browse/O2-7309

Co-Authored-By: Claude Opus 5.5 <[email protected]>
@sawenzel sawenzel mentioned this pull request Nov 9, 2026
Share the scaled TPC distortions between the digitizers of a job AliceO2Group/O2DPG#2541
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@shahor02 shahor02 Awaiting requested review from shahor02 shahor02 will be requested when the pull request is marked ready for review shahor02 is a code owner
@davidrohr davidrohr Awaiting requested review from davidrohr davidrohr will be requested when the pull request is marked ready for review davidrohr is a code owner
@wiechula wiechula Awaiting requested review from wiechula wiechula will be requested when the pull request is marked ready for review wiechula is a code owner

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@sawenzel
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