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EDM4hep Discussion
EDM4hep Live Notes
==================
Date: Oct 14, 2025
Indico: https://indico.cern.ch/event/1600615/
Connected: Juraj, Andreas, Andre, Juan, Thomas, Brieuc, Mateusz
Apologies:
### Upcoming workshops / conferences
https://github.com/orgs/key4hep/projects/4/views/1
## Progress and discussion
### Logo Poll
- **Final chance to vote**
- https://github.com/orgs/key4hep/discussions/3
## Podio
* https://github.com/AIDASoft/podio/pulls
* https://github.com/AIDASoft/podio/issues
* https://github.com/orgs/AIDASoft/projects/2/views/1
### New tag v01-05
* https://github.com/AIDASoft/podio/releases/tag/v01-05
* DD4hep v01-32 (and previous) cannot use this
* Need https://github.com/AIDASoft/DD4hep/pull/1480
### Merged PRs
- Add an indicator for subset collections to podio-dump [#855](https://github.com/AIDASoft/podio/pull/855)
- podio-merge-files: import later for faster help messages and use get_reader [#857](https://github.com/AIDASoft/podio/pull/857)
- Add documentation about some of the existing tools [#854](https://github.com/AIDASoft/podio/pull/854)
- Generate old POD versions into a version namespace [#803](https://github.com/AIDASoft/podio/pull/803)
### `isValid()` for collections does not return what one would think that it means
* https://github.com/AIDASoft/podio/issues/853
* https://github.com/AIDASoft/podio/pull/860
* Deprecate `isValid` and replace by `hasID` (same behavior, more approriate name)
* What to do with podio version once `isValid` is removed?
* Not ussed too much(?)
### `ROOTReader` cannot read a file that only contains subset collections
* https://github.com/AIDASoft/podio/issues/859
* Dictionaries not loaded if only subset collections are in file
* Not sure if there is an easy fix for this that doesn't tank performance
* Files with only subset collections are effectively useless, as there is no data to point to.
* [ ] Add a warning that a file only contains subset collections
### Add the possibility to extract collections from a Frame
* https://github.com/AIDASoft/podio/pull/856
* Feature request from Acts (Paul)
* Not sure if the actual problem they have is not better solved with an appropriate DD4hep ParticleHandler
* Aware of the existing functionality in podio to do the remapping (e.g. `clone`-ing collections and manually re-setting relations)?
* could also use the type lists that we generate to do some variadic template things?
* Might still be useful as an "expert feature"?
* Could be useful for RDataFrame for mutating a collection(?)
### Improve error messages when readers encounter problems
* https://github.com/AIDASoft/podio/pull/851
* https://github.com/AIDASoft/podio/issues/847
* https://github.com/AIDASoft/podio/issues/848
* Give users a bit more information than simply running into uncaught `std::bad_function_call`
* Can we do better for error recovery?
* For ROOT: we either get the full Frame or nothing, but we could probably do this on a collection basis as well(?)
* For SIO: we could tackle this on a collection basis (not done in PR yet)
* For `Frame` we already do the permissive way of returning an empty collectoin or a `nullptr` if not found.
* Do the same for the Readers for consistency
### Schema evolution
* Refactored testing in podio related to schema evolution quite extensively
* Several PRs in flight, need to clean them up and figure out the actually necessary changes
* https://github.com/AIDASoft/podio/pull/845 (**ready for review**)
* https://github.com/AIDASoft/podio/pull/828
### Make sure to not consume all available memory on garbage data
* ~~https://github.com/AIDASoft/podio/pull/842~~ https://github.com/AIDASoft/podio/pull/846
* Discovered in testing, where it can be mitigated [#836](https://github.com/AIDASoft/podio/pull/836)
* [ ] Try to make a reproducer and see if this is a ROOT issue
* [ ] Verify this crashes with debug builds (of podio) of Key4hep stack
* Can we try to store some "parity" information, e.g. the actual collection size to check whether what we read is correct?
* Might break with `size() == 0`, i.e. empty collections
* Not yet happened in the wild, only occured in testing so far, but once schema evolution is in place people might stumble over this
* Solve later?
* Can we catch this earlier?
* E.g. check information from ROOT file to see if things match
* No clear decision yet how to best handle this
* [x] Confirm that RNTuple is not affected
* [ ] Review and merge
## EDM4hep
* https://github.com/key4hep/EDM4hep/pulls
* https://github.com/key4hep/EDM4hep/issues
* https://github.com/orgs/key4hep/projects/5
### Merged PRs
- Use edm4hep.h in edm4hep2json to avoid hardcoding the types [#443](https://github.com/key4hep/EDM4hep/pull/443)
### Do not build and extra library for the old schemas
* https://github.com/key4hep/EDM4hep/pull/452
### Rework the generator related information structs
* https://github.com/key4hep/EDM4hep/pull/446
* https://github.com/key4hep/EDM4hep/issues/409
* Remove `GeneratorPdfInfo` / partially merge it into `GeneratorEventParameters`
* **Existing files with these datatypes will break**
* [x] Has anyone used these outside of k4GeneratorsConfig?
* [ ] Check if [podio#851](https://github.com/AIDASoft/podio/pull/851) can be used here to not break
* [x] Verify that we can indeed store all the necessary information in this class
* Keep in mind that we also have file and event level parameters to store more things
* Seems to be a rather minimal set. Adding new things is easier (schema evolution wise than removing /changing existing thigns)
* Not bumping schema version (has already been bumped for MCParticle changes)
## Converter & MarlinWrapper
## AoB
* ROOT release plan: https://indico.cern.ch/event/1590848/contributions/6704085/attachments/3146168/5586196/251001%20-%20ROOT%20Q3%202025%20Report.pdf (S13)
## Next meeting:
* Oct 28, 09:00
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