Splitting big root files to smaller ones

ROOT
1

Hi experts,
I have a big root file containing a tree which has more than 5million
entries in it.
When I try to call tree->GetEntries(); since the number of entries
is so large it takes a long time and finally because it overloads the memory it aborts and simply goes out of ROOT.
Is there any way to split a big root file to smaller files.
Thanks,
Majid

2

he time to call tree->GetEntries must be independent of teh Tree size.
You must have another problem. My guess is that you have created
a memory resident tree.
Could you send the output of tree->Print() ?

Rene

3

Hi Rene,
I have copied the output of root tree show and print.
When I run it on a pc with 512MB RAM it works after a long time but
with lxplus it crashes.
Cheers,
Majid

[lxplus055] ~/scratch0/newtest/HTBDAQ_data/tools > root
  *******************************************
  *                                         *
  *        W E L C O M E  to  R O O T       *
  *                                         *
  *   Version   4.03/02  10 February 2005   *
  *                                         *
  *  You are welcome to visit our Web site  *
  *          http://root.cern.ch            *
  *                                         *
  *******************************************

FreeType Engine v2.1.3 used to render TrueType fonts.
Compiled for linux with thread support.

CINT/ROOT C/C++ Interpreter version 5.15.159, Nov 14 2004
Type ? for help. Commands must be C++ statements.
Enclose multiple statements between { }.
 fdlopen 
root [0] TFile f("min15E.root");
root [1] t->Print();
[lxplus055] ~/scratch0/newtest/HTBDAQ_data/tools > root
  *******************************************
  *                                         *
  *        W E L C O M E  to  R O O T       *
  *                                         *
  *   Version   4.03/02  10 February 2005   *
  *                                         *
  *  You are welcome to visit our Web site  *
  *          http://root.cern.ch            *
  *                                         *
  *******************************************

FreeType Engine v2.1.3 used to render TrueType fonts.
Compiled for linux with thread support.

CINT/ROOT C/C++ Interpreter version 5.15.159, Nov 14 2004
Type ? for help. Commands must be C++ statements.
Enclose multiple statements between { }.
dlopen 
root [0] TFile f("min15E.root");
root [1] t->Show(1);
[lxplus055] ~/scratch0/newtest/HTBDAQ_data/tools > ls -l min15E.root
-rw-r--r--    1 hashemim zh       75244574 Apr 21 17:02 min15E.root
[lxplus055] ~/scratch0/newtest/HTBDAQ_data/tools >
4

You forgot to include the result of tree->Print()

Rene

5

Hi Rene,
No it is correct.
I mean it takes a long time and then just simply the ROOT session
is killed and it goes to shell command prompt without any output.
Cheers,
Majid

6

OK, this confirms my initial guess. You have create a memory-resident
Tree on a machine with a lot of memory, saved it to a file.
Now you are trying to read it on a machine with less memory.

A memory-resident tree is typically generated by mistake with

TTree *T = new TTree(“T”,…)
TFile *f = new TFile(…);
instead of
TFile *f = new TFile(…)
TTree *T = new TTree(…

Rene

7

Dear Rene,

I have a big root file in my remote area and I want to copy it to my local system but problem is I am seeing disk quota exceed so Could you give any hints how to splits it into number of small root files sothat I can copy easily and later I can add it by TChain.

Thanks in advance,
Nibedita.