Make a huge root file

Dear experts,
I have many root file with a total of 300GB. When I merge at then end it does not work, probably the merge file become too big. Do you know how I can do that?


The better answer is actually a question: Why would you want to do that?! I’d recommend ~500 MB to 1 GB per file. See also Can I disable the maximum root file size?

Dear behrenhoff,
well as physicist we manipulate many files right?.. So I need these files.

Dear Behrenhoff,
is it possible to disable the maximum root file size while doing “hadd file.root huge1.root huge2.root”? or should I wrote a code?

Still, why do you want to join? “I need the files” is not a reason for joining.

What contents do you want to join?

Trees? In that case: just don’t join / or just join a few files! (you can use a TChain)
Histograms? Use hadd -T to exclude trees from the join.

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Dear behrenhoff,
I have many root files in a directory, I currently have a code which take 1 root file to plot the tree variables. Maybe I could do a of loop the root file instead of nerging them… Is there an example how to do that?

See TChain


Dear behrenhoff and pamputt,

yes “TChain” is the best option in my case. Thank you for your help.


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