Hi,
these kind of issues are usually due to a multi-thread snapshot of a ROOT file with highly suboptimal clustering (e.g. each entry of the input TTree is zipped by itself).
What happens in those cases is that reading takes much less than writing entries, so (uselessly large) unwritten buffers of data start accumulating in memory. See ROOT-9133.
So let’s check if you are indeed seeing ROOT-9133.
@Eddy_Offermann do you see elevated RAM usage when executing the macro with root -l -b -q or only when executing with EnableImplicitMT (i.e. root -l -b -q -t)? (will be running it myself asap)
@vfranco can you confirm that removing EnableImplicitMT() from your macro “fixes” the issue?
If yes, you can either check the clustering of your file with
TTree *t = nullptr;
file.GetObject("treename", t);
auto it = t->GetClusterIterator(0);
for (auto entry = it.GetStartEntry(); entry != t->GetEntries(); entry = it.GetNextEntry())
std::cout << entry << std::endl;
or something similar (have not tested the code but should give you an idea)
or as @Danilo suggests you can share your file with us.
Cheers,
Enrico