10–13 Sept 2018
Academy of Sciences and Arts (Akademija nauka i umjetnosti Bosne i Hercegovine)
Europe/Sarajevo timezone
FUN WITH DATA!

Reliable Histogram Aggregation for the LHCb software trigger

12 Sept 2018, 16:45
15m
Academy of Sciences and Arts (Akademija nauka i umjetnosti Bosne i Hercegovine)

Academy of Sciences and Arts (Akademija nauka i umjetnosti Bosne i Hercegovine)

7, Bistrik Sarajevo 71000, Bosnia and Herzegovina https://goo.gl/maps/Ct9jKrSER4z
Presentations Experiments Perspective

Speaker

Dr Roel Aaij (Nikhef National institute for subatomic physics (NL))

Description

The second stage of the LHCb software trigger application consists of an
up-front event reconstruction followed by approximately 500 independent
event selections. Monitoring of the performance of the reconstruction and
selections is crucial to detect and address issues that may appear as soon
as possible. To this end, each process produces approximately $3 * 10^3$
monitoring histograms, resulting in $1.35 * 10^8$ histograms that need to
be aggregated. To achieve this, a tiered architecture of monitoring
infrastructure tasks has been put in place, which separately propagates
histogram descriptions and histogram increments using ØMQ. As this separation
is not possible with ROOT, it is based on standard containers and a few
custom classes serialized using boost::serialization.

As a result of the asynchronous processing, different nodes may process
data from different data-taking intervals. This results in up to $5 * 10^{5}$
ROOT histograms, belonging to 300 data-taking intervals, that need to be
written to a single file per interval every few minutes. Improvements in
ROOT's parallelization have allowed simplification of the code, but some
bottlenecks are still present.

Primary author

Dr Roel Aaij (Nikhef National institute for subatomic physics (NL))

Co-author

Mr Stefano Petrucci (University of Edinburgh, CERN)

Presentation materials