Revisit use of HitPattern in DataFormats/Scouting

[makortel]

#31962 added use of complex data structure reco::HitPattern in Run3ScoutingMuon. It was agreed to revisit that usage before the data taking of Run3 to either remove the usage (as too heavy for production use), or replace with e.g. a frozen version of HitPattern that could be easy to guarantee to be read in any later release.

The purpose of this issue is to act as a reminder.

[cmsbuild]

A new Issue was created by @makortel Matti Kortelainen.

@Dr15Jones, @dpiparo, @silviodonato, @smuzaffar, @makortel, @qliphy can you please review it and eventually sign/assign? Thanks.

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[makortel]

assign core,hlt

[cmsbuild]

New categories assigned: core,hlt

@Dr15Jones,@smuzaffar,@makortel,@Martin-Grunewald,@fwyzard you have been requested to review this Pull request/Issue and eventually sign? Thanks

[makortel]

Any news yet on whether HitPattern like information will be needed for Run3ScoutingMuon? @jsalfeld

[jsalfeld]

@mmasciov wanted to check

(cc'ing @dsperka )

[silviodonato]

I remember about this issue. Thank you Matti and Jakob for raising this up. I will keep this in mind that this need to be solved much before the data taking.
cc @acostad

[makortel]

Is there any chance this question could be resolved already for 12_1_0?

[mmasciov]

@makortel: if it is OK with you, given that recent measurements by @dsperka showed that HitPattern for Run3ScoutingMuon shall not be heavy at all, I'll go with option (2). I.e., I'll make a frozen copy of HitPattern for scouting, and use such copy in Run3ScoutingMuon.

[mmasciov]

As for the timeline, this option should be fast, and in time for 12_1_0 (before 19th of October).

[makortel]

Thanks @mmasciov, that option is fine. For the record, could you give pointer to

@dsperka showed that HitPattern for Run3ScoutingMuon shall not be heavy at all

?

[mmasciov]

The latest slides showing that muons are little in size should be: https://indico.cern.ch/event/1066775/contributions/4492263/attachments/2301466/3914859/scouting_event_content_xpog.pdf
However, @dsperka may have more recent/accurate numbers.

[VinInn]

If possible I would change current HitPattern to

template<int N>
HitPatternT;

and then have to aliases
using HitPattern = HitPatternT<kOfflineHitPatternSize>;
and
using HitPatternScouting = HitPatternT<kScoutingHitPatternSize>;

if (kScoutingHitPatternSize==kOfflineHitPatternSize) memcpy is enough
if (kScoutingHitPatternSize<kOfflineHitPatternSize) a custom copy constructor should work.
I do not expect kScoutingHitPatternSize>kOfflineHitPatternSize will ever happen....

up to the expert to guess the proper versioning mechanism for the offline version

[slava77]

if the past can be a reference for possible developments, the size of the array is not the only thing that can change; other data members (indices) can change as well.

[missirol]

+hlt

• addressed by @mmasciov in Revisit usage of HitPattern in DataFormats/Scouting #37149

[makortel]

+core

[cmsbuild]

This issue is fully signed and ready to be closed.