[ROOT] tree->ChangeFile(....) and output rootfile larger than textfile.

From: zaldy (zaldy@neutrino.kek.jp)
Date: Thu Aug 07 2003 - 17:08:25 MEST 

Hi EveryOne,

I have two items which are new to my experience with root now, and I 
dont understand them very well. I'd appreciate very much your help.

FIRST: ROOT Tree too large ...
^^^^^^^^^^^^^^^^^^^^^^^^^^
Can someone tell me how to use the tree->ChangeFile(TFile * file)?

I just learned it from ROOT FAQ, that this is used when root tree size 
exceeds the 2GB limit. Bbut I don't know how to insert them along 
which line, or next to what line. Am having trouble saving a large root 
file greater than 2 GByte Limit.


SECOND: ROOT File Tree larger than the source file? 
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
I have a source file(text file), actually 2 columns, an integer and a 
Float

        Ch  Time 
i.e.,   4   20567.90
        8   38930.34
       15   24523.67 
       .............
       .............

There are about 380,000 lines of the above format. So I decided to create 
a tree 
like:    ...................
         ....................
         Int_t comp = 1;
        TFile * f     = new TFile("out.root","NEW");
        f->SetCompression(1);
        TTree * tree  = new TTree("T", "myTree");
        tree->SetAutoSave(1000000000);         

        tree->Branch("Ch",&Ch,"Ch/I");
        tree->Branch("Time",&Time,"Time/F");
        
        while(fgets(.......)) { 

        ........filling.....

        Int_t nb = 0;
        nb += tree->Fill(); 
        tree->AutoSave(); 
        tree->Print();
        tree->Write          
        ......... 
        }

But during implementation, I was disturbed that the output sizeof the root 
file is larger than the source text file by several (~5)factors. Do you 
know what is going on here? That  means that the way I created a tree is 
not "efficient"; and filling of the  tree takes some time. I figure out 
that obtaining a histogram by directly  filling the contents from the 
source file maybe faster than obtaining a  histogram from a rootproduced 
tree (later).

But having a root tree is still more advantageous. 
How do we rewrite the above script?

Thank you for bearing with me.


PS.
root version 3.05/05
gcc 3.2.2 RedHat 9
-- 

--------------------------------------------------------
                   Zaldy A. Nawang 
                   PS Users Room 2
                   Yon Gokan, 
                   E362, Neutrino Group, 
                   IPNS, KEK, 
                   Japan 
                    
                   e-mail: zaldy@neutrino.kek.jp
                   Tel. No. : (81) 029864 - 5387
--------------------------------------------------------

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