Loop() method runs slow

ROOT
1

Hi,
I have thousands of root files with my desired branches in it. I generated a class from MakeClass method of root and read all the file in the Loop() method. The root files are added in a TChain so that I can read them all in one go. But this takes a lot of time (> 10 hours).

But if create some short root files combining the above root files (where I have only few branches in it) then the Loop() method runs within an < 1/2 hour.

I am accessing the same variable in either case inside the Loop() method.

Is there a way so that it can be faster in the 1st case so that I do not have to go through 2nd case?

Any suggestions are welcome.
with best regards,
sushil

2

Just to forgot to mention that I create ans shared object to run the code.

-sushil

3

It is likely that you are always reading all the branches of your Tree where in fact you should only read the branches that you use.
-call mytree.SetBranchStatus("*",0), then mytree.SetBranchStatus(“branchName”,1) for all the branches that you want to activate, then mytree.GetEntry(i)
-or better solution if you read only a fee branches, call branch.GetEntry(i) instead of mytree.GetEntry(i)
-see also how to use the TreeCache in the 5.26 release notes

Rene

4

Hi Rene,

I try SetBranchStatus("bname",0) for those branch which are not needed in loop method. It improves a bit but still taking a lot of time compare to case where I have few branches and combining them to a single file.

I tried these llines also :

Long64_t nentries = fChain->GetEntriesFast();
fChain->SetCacheSize(10000000);
fChain->AddBranchToCache("*");

But it complaints;
class TTree’ has no member named 'AddBranchToCache

I am using FNAL cluster where root 5.22 is available so do not know I can make it work there.

Thanks.
with best regards,
sushil

5

you must use 5.26 or newer

Rene