Re: [ROOT] Wierd I/O Speed Behaviour

From: Rene Brun (Rene.Brun@cern.ch)
Date: Fri Sep 27 2002 - 19:10:05 MEST


Hi Roger,

Could you move to version 3.03/09 and tell me if this symptom persists?
If it does, please send me the result of
  tree.Print();
for your old and new Trees

Rene Brun

On Fri, 27 Sep 2002, Roger Moore wrote:

> Converting some analysis code from using a ROOT-tuple to using a ROOT Tree
> (i.e. from individual variables in arrays to real objects) I've noted some
> very strange behaviour with the readout speed.
> 
> With the old ROOT-tuple I could vastly increase the speed of the code by
> turning off all branches and then just turning back on the branches that I
> was interested in looking at.
> 
> However with the shift to the ROOT-Tree whose branches consist of
> TClonesArray the exact reverse is true! When I turn off all the branches
> except the one I am interested in the GetEntry() method of the tree takes
> 50-60ms to execute. However when I to not turn the branches off the time
> taken for GetEntry() drops to ~3ms/event.
> 
> Does anyone understand what is going on here? I don't see how not
> unpacking a branch can possibly slow the code down!
> 
> I'm using ROOT 3.03/07 and in both cases I only do SetBranchAddress (to a
> TClonesArray) for the branches I am interested in reading out.
> 
> Roger
> 



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