Hadd of root files gets "Killed"

Dear Experts,

I’m running into troubles when trying to use hadd to merge some root files I have.
After hanging for a while, I get the following error:


and an empty output file.
I have 520 root files with a total size of 11GB.
They live in the following directory on EOS at CERN:


I tried to use the “-n 50” option to open small chunks of 50 files, but this didn’t fix the issue.
Am I going in the right direction? Or should I try something different?


UPDATE: the merging worked if I use the “extreme” option -n 1 (i.e, only one file opened each time). I guess that there should be some optimal point (5, 10 files or similar).

Most likely with too many files open at once, the memory use of hadd is too large for your system.


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