How Merge root files
Ganga
The easiest way is to let ganga handle it with with the
RootMerger()
j=Job(t)
j.merger = RootMerger()
j.merger.files = ['out-file.root']
This worked fine for me for ages until the merging program this calls stayed at 100% forever and the python memory usage consumed everything available. So I had to merge the files manually...
Merging manually
The program hadd is the one that the root merger calls to merge the files
hadd ~/outputfile.root ~/input1.root ~/input2.root [...]
When running manually this segfaulted on my root file, it turned out to be because I had run
SetupProject Ganga at the beginning by starting a new session and doing
SetupProject DaVinci the hadd program no longer segfaulted.
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ThomasBird - 2010-08-04