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Read MC kinematics per event in MatchITSTPCQC and fix a reader leak - #15914
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This fixes a memory leak in the MCKinematicsReader destructor. - The destructor never deleted the per-event track vectors that are still cached.
This reduces the memory of the MC mode of the ITS-TPC matching QC from the size of all kinematics of the TF to that of the largest event. - The physical-primary flag of all needed labels is now resolved event by event. - Each event is released after use, whereas before every touched event stayed cached. - The histograms are unchanged (92 compared bin by bin, same entries). Peak memory of the `o2-qc` task on one PbPb timeframe of 8 orbits (28 signal events, 75.6M MC tracks): | | before | after | |---|---:|---:| | `o2-qc` device (PSS) | 5.6 GB | 1.45 GB | | task total (PSS) | 7.1 GB | 2.9 GB | | wall time | 35 s | 41 s | Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
This makes the MCKinematicsReader non-copyable. - The destructor deletes the cached track vectors, so an implicit copy would free them twice. - No copy of a reader exists in AliceO2.
shahor02
approved these changes
Oct 8, 2026
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This PR reduces the memory of the MC mode of the ITS-TPC matching QC by reading the MC kinematics one event at a time, and fixes a leak in the
MCKinematicsReaderdestructor.MatchITSTPCQCcached the tracks of every event it touched, only to evaluateisPhysicalPrimaryfor a single track each. For PbPb with Geant4 a signal event holds about 2.7 million MC tracks, so the cache grows to several GB. Separately, the destructor ofMCKinematicsReadernever deleted the per-event track vectors that were still cached, which shows as 3.9 GB leaked at exit in heaptrack.The physical-primary flag of all labelled tracks is now resolved event by event, and each event is released after use. The destructor now deletes what is left in the cache, and since the reader owns these vectors its copy operations are deleted. The effect on one timeframe of 8 orbits (nightly MC
LHC22k4_nightly, run 311511, 28 signal events, 75.6M MC tracks):o2-qcdevice (PSS)This task is one of three that run together in the QC pass of these jobs and bring it to a median of 27 GB; the other two are in a companion QualityControl PR.
Note that the histograms are unchanged: the 92 histograms of the task have identical bin contents and entries before and after.
The measurements use the recompiled files preloaded into
o2-qcof the CVMFS dailyv20261007-1. The branch is not yet built on currentdev.Assisted by Claude Code.