Process killed when merging big jobs

[bundocka]

Description

When merging many sub jobs/root files from large datasets (typically around 300 I think), process is killed after some time. Need to have an easy way to split merging up into steps as takes too long when many root files need to be merged.

Steps/code to reproduce issue

cmsl1t -c all2017.yaml -r --hist-files '

Expected results

Produces merged root file and plots.

Actual results

"Killed"