Unbearably slow TChain issues

ROOT
1

Hello,

I am trying to string lots of small files together and then do an analysis on that mass of data. I can make the program run, but its so slow as to be functionally unusable. Here is the relevant snippet:

TChain* events = new TChain("events");
TString list_file = "list.txt";
ifstream in;
in.open(list_file);
TString run_num;

while(true) {
        //Set up the string handling
         TString run_prefix = "Run0";
         //Read each individual line from list.txt into the variable run_num;
         in >> run_num;
         //If you reach the end of file or something otherwise is fucked up, quit the file.
         if(!in.good()) break;
         run_prefix+=run_num;
         //Set up the logic for the allpulses set of file. Each root file has one and only one associated with it.
         TString pulses = run_prefix;
         pulses+="_allpulses.root";
         //2Chainz
         TChain* run_chain = new TChain("events");
         TChain* pulse_chain = new TChain("pulse_info");
         run_prefix+=".root";
         TString run_file = "/file/path" + run_prefix;
         TString pulse_file = "/file/path" + pulses;
         //cout<<pulse_file<<std::endl;
         //Add all the chains together.
         pulse_chain->Add(pulse_file);
         run_chain->Add(run_file);
         events->Add(run_chain);
         events->AddFriend(pulse_chain);
         //Delete all the unnecessary objects to prevent a segmentation fault.
        delete run_chain, run_file, pulse_file, run_prefix;

Each event in the chain events is then put through the analysis. Does anyone know why this is unbearably slow?

2

Dear joshuacarey,

Can you elaborate more on what you mean by “unbearably slow”?
Did you check that the final “event” is what you wanted (w/ events->ls() or events->Print())?
How many data the final “events” contain?
How does it compare with processing a single file?

Also note that in your snippet run_file and pulse_file are not on the heap, so you should not ‘delete’ them.

G Ganis