Re: [ROOT] Size of root file after writing a subset of a tree

From: Rene Brun (Rene.Brun@cern.ch)
Date: Tue Jan 27 2004 - 19:00:39 MET


Hi Frank,

Could you send the result of 

chain1->Print();
xtree0->Print();

Rene Brun


Frank Winklmeier wrote:
> 
> Hi Rene,
> 
> sorry about that. Here it is:
> 
> TChain *chain1 = new TChain("xtree");
> chain1->Add("/hep42/frank/root/xjpsi-*.root");
> 
> TFile f1("/hep42/frank/root/xjpsi-B0.root","recreate");
> TTree *xtree0 = chain1->CopyTree("m0B0>0");
> f1.Write();
> 
> Frank
> 
> On Tue, 27 Jan 2004, Rene Brun wrote:
> 
> > Frank,
> >
> > Please send your real code. In your snippet you have
> > TFile f("subset.root");
> > this should be
> > TFile f("subset.root","recreate");
> >
> > Rene Brun
> >
> > Frank Winklmeier wrote:
> > >
> > > Hi,
> > >
> > > I want to select a subset of a tree which is split over several files and
> > > save this subset to one new file. Everything works fine but the resulting
> > > file size is much bigger than the sum of the input files.
> > >
> > > I start with:
> > >
> > > TChain *chain = new TChain("tree");
> > > chain->Add("data-*.root");
> > >
> > > // there is data-1 to data-21, each about 13 MB
> > >
> > > TFile f("subset.root");
> > > TTree *subtree = chain->CopyTree("m0b0>0");
> > > f.Write();
> > >
> > > The resuling size of subset.root is about 560 MB !!!
> > > But the total size of the (unfiltered) input is only about 270 MB.
> > > The compression level is 1 in all the files.
> > > The selection criteria "m0b0>0" selects about 50% of all entries.
> > > I am using RooT version 3.10-01 on RH9.
> > >
> > > How is that possible? Why is the compression so much worse for the subset?
> > >
> > > Thanks,
> > > Frank
> >



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