SLB: Application of the relation table algorithm to store MVA score

Description

Application of Rec!4126 (merged) to SL sprucing lines. We use the relation table format to remove the duplicate pions persisted so far in the extra_outputs.

The tool implemented in Rec!4126 (merged) is relevant for the SL WG as it enables the possibility to rank offline the extra particles on the basis of the MVA score and pick, with proper functor implemented in the same MR, the desired candidate.

Impact on the BW

A negligible impact on the BW is expected, with a small reduction on the event size per SL line with selective persistency turned on. This is related to the removal of duplicated extra particles persisted offline.

Changes in BW in different configurations (evaluated on 10k minbias sample):

persistency	BW (GB/s)
extra tracks duplicated (current version)	0.181
extra tracks not duplicated	0.180

Current status

The current MR removes the duplicates from the Selection of particles from the rest of the event persisted during the sprucing. Adding the relation table between signal candidates and particles from the rest of the event, weighted by the MVA score, makes the test fail with the following error.

LHCb__SelectivePacker_cd1c82bb        ERROR bool LHCb::{anonymous}::{anonymous}::Item<KeyedContainer<ValueType, Mapping> >::emplace(const ValueType*) [with ValueType = LHCb::Particle; Mapping = Containers::KeyedObjectManager<Containers::hashmap>] : attempt to add to locked item (potential circular dependency?)
LHCb__SelectivePacker_cd1c82bb        ERROR Maximum number of errors ( 'ErrorMax':1) reached.
HLTControlFlowMgr                     FATAL Event failed in Node HltPackedBufferWriter/HltPackedBufferWriter_97f7c229
HLTControlFlowMgr                      INFO Application return code set to 3
HLTControlFlowMgr                     FATAL Event 861 on slot 0 failed!
HLTControlFlowMgr                     FATAL *** Too many consecutive failures 1, stopping now ***

Full log: log.txt

The persistency of the relation table is therefore turned off, we persist only a selection of extra particle and we re-build the relation table offline for doing the ranking

FYI: @graven, @sstahl, @mveghel, @decianm, @mfontana, @nskidmor