[ROOT] Performace Tree Reading

From: Norbert Danneberg (norbert.danneberg@psi.ch)
Date: Mon Nov 20 2000 - 16:49:51 MET 

Hi , 

I recently changed my code to use Eventlists before looping over a TChain.
First I create a Eventlist via TChain::Draw(">>elis","selction") 
Second I read from the Tree only entries which are in the eventlist 
via 
for (Int_t i =0; i< NSelectedEvents; i++){
    GetEvent(MyList->GetEntry(i));
}
The list contains approx 10 percent of the events in the TChain. (20 Mio)
It seems that the correct events are extracted from the tree, but 
the performace does not improve. The running process uses approx
only 18 - 20 percent of the availible CPU time. I guess root tries to
find the entry but since ist is not the next in the tree but somwhere 
else it has to access the disk for each GetEntry().

Does it help to increase the BasketBuffer Size ? 
Or maybe fmaxvirtual size ?


Thanks

Norbert

-- 

Norbert Danneberg

ETH Zurich - Institute for Particle Physics
  Laboratory for Nuclear Physics          Phone.: +41-1-633-2034
  Hoenggerberg                            Fax.:   +41-1-633-1067
  CH-8093 Zurich  


ETH Zurich - Institute for Particle Physics
  Paul Scherrer Institute                 Phone.: +41-56-310-3284
  CH-5232 Villigen PSI                    Fax.:   +41-56-310-4362

email: Norbert.Danneberg@psi.ch

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