Reduce memory churn at Geant4 initialisation of geometry

[civanch]

PR description:

Reduced number of copies of geometry objects during initialisation of Geant4 geometry.
Correctness of this PR should be confirmed by identical results.

PR validation:

private runs

if this PR is a backport please specify the original PR:

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• verify that the PR is really intended for the chosen branch
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[cmsbuild]

The code-checks are being triggered in jenkins.

[cmsbuild]

The code-checks are being triggered in jenkins.

[cmsbuild]

+code-checks

Logs: https://cmssdt.cern.ch/SDT/code-checks/cms-sw-PR-27519/10879

• This PR adds an extra 16KB to repository

[cmsbuild]

A new Pull Request was created by @civanch (Vladimir Ivantchenko) for master.

It involves the following packages:

SimG4Core/Geometry

@cmsbuild, @civanch, @mdhildreth can you please review it and eventually sign? Thanks.
@makortel this is something you requested to watch as well.
@davidlange6, @slava77, @fabiocos you are the release manager for this.

cms-bot commands are listed here

[civanch]

please test

[cmsbuild]

The tests are being triggered in jenkins.
https://cmssdt.cern.ch/jenkins/job/ib-run-pr-tests/1466/console Started: 2019/07/14 16:10

[cmsbuild]

+1
Tested at: 6105757
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-480a93/1466/summary.html

[cmsbuild]

Comparison job queued.

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-480a93/1466/summary.html

Comparison Summary:

• No significant changes to the logs found
• Reco comparison results: 2 differences found in the comparisons
• DQMHistoTests: Total files compared: 32
• DQMHistoTests: Total histograms compared: 3081858
• DQMHistoTests: Total failures: 2
• DQMHistoTests: Total nulls: 0
• DQMHistoTests: Total successes: 3081534
• DQMHistoTests: Total skipped: 322
• DQMHistoTests: Total Missing objects: 0
• DQMHistoSizes: Histogram memory added: 0.0 KiB( 31 files compared)
• Checked 133 log files, 14 edm output root files, 32 DQM output files

[civanch]

+1

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next master IBs (tests are also fine). This pull request will now be reviewed by the release team before it's merged. @davidlange6, @slava77, @smuzaffar, @fabiocos (and backports should be raised in the release meeting by the corresponding L2)

[fabiocos]

In the total RSS seen in wf 11624. there is a small reduction from <Metric Name="PeakValueRss" Value="523.309"/> to <Metric Name="PeakValueRss" Value="513.125"/> . Is this the expected effect?

[civanch]

@fabiocos , yes, such type small effect is expected. Another improvement - simplification of the code.

[fabiocos]

+1