void plot_db_stat(const char* filename) {

  TFile* f;

  f = (TFile*) gROOT->GetListOfFiles()->FindObject(filename);
  if (! f) {
    f = new TFile (filename);
  }

  TTree* tree = (TTree*) f->Get("dbstat");

  TCanvas* c1 = new TCanvas("c_db_stat","DB statistics",0,0,600,800);
  c1->Divide(1,2);
  c1->cd(1);
  gPad->SetLogy(1);
  tree->Draw("fTimeGets");
  c1->cd(2);
  tree->Draw("fTimeGets:fTableNumber");
}