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Forum: Analysis
Re: Question Maximum number of graphs in an ntuple (Patrick Asenov)
Date: 20 Aug, 2018
From: Guy Barrand <Guy Barrand>

  Hi Patrick

> Does anyone know what is the maximum number of plots that I can save in a single ntuple in ROOT?
> I'm interested in storing 266240 graphs (regarding the pixels of two detector modules) in one place.

 It is not clear for us what you want to know or do...

 If it is about the number of TGraph objects that you can store in a TTree attached to a TFile, by using ROOT
itself (within a Geant4 context or not), then this is a question to be asked in the ROOT forum. (From what
I know of the ROOT/IO, if you arrange to store your TGraph objects in one branch, the only limit should
be on the size of the file on the file system, which is... large).

 Within Geant4/analysis and g4tools/wroot code, right now we store only histograms and flat ntuples
(no plots and TGraph equivalent).

 Anyway, if you intend to book/handle a flat ntuple with 266240 columns (!), you have to use (attempt
to use !) the "row-wise" mode introduced in Geant4/10.5. With a column-wise mode, where each column is
mapped on a branch and for which a default buffer of 32K is created, you will explode your memory...
(266240*32K is around 8.5 Gbytes).

  Regards. Guy

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1 Ok: Re: Maximum number of graphs in an ntuple   (Patrick Asenov - 21 Aug, 2018)
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