TTreeCache does not work for TBranch::GetEntry

ROOT
1

Hi,

I just found that I TTreeCache does not work for TBranch::GetEntry().

TTreeCache works for TTree::GetEntry,

TFile *f = TFile::Open("NTUP_TOPMU.3.root");
TTree *physics = (TTree*)f->Get("physics");
physics->SetCacheSize(10*1024*1024);
physics->SetCacheLearnEntries(1);
Int_t nevt=physics->GetEntries();
physics->SetBranchStatus("*",0);
physics->SetBranchStatus("RunNumber",1);
physics->SetBranchStatus("EventNumber",1);
for (Int_t i=0; i<nevt; i++) {
   physics->GetEntry(i);
}
physics->PrintCacheStats();

And I got the result:

But if I switched from TTree::GetEntry to TBranch::GetEntry, TTreeCache does not work:

TFile *f = TFile::Open("NTUP_TOPMU.3.root");
TTree *physics = (TTree*)f->Get("physics");  
physics->SetCacheSize(10*1024*1024);
physics->SetCacheLearnEntries(1);
Int_t nevt=physics->GetEntries();
physics->SetBranchStatus("*",0);
physics->SetBranchStatus("RunNumber",1);
physics->SetBranchStatus("EventNumber",1);
for (Int_t i=0; i<nevt; i++) {
   physics->GetBranch("RunNumber")->GetEntry(i);
   physics->GetBranch("EventNumber")->GetEntry(i);
}
physics->PrintCacheStats();

and got the result:

Obviously TTreeCache was not used at all.

According to the source code of TTree, TTree::GetEntry just reads in a list of branches via TBranch::GetEntry, plus reads in list of friends.

I tried ROOT 5.28.00g, 5.30.03 and 5.32.oo-rc2, and got the same result.

I can not understand why TTreeCache works for TTree::GetEntry but not for TBranch::GetEntry.

–Shuwei

2

Hi Shuwei,

In order to use the TTreeCache when using TBranch::GetEntry, you need to also explicitly move the TTree cursor by calling TTree::LoadTree.

Typically code calling TBranch::GetEntry looks like (as this code will work for both TTree and TChain):for (Long64_t i=0; i<physics->GetEntriesFast(); i++) { Long64_t localEntry = physics->LoadTree(i); physics->GetBranch("RunNumber")->GetEntry(localEntry); physics->GetBranch("EventNumber")->GetEntry(localEntry); }

Cheers,
Philippe.