TRef and TChain::Merge

ROOT
1

Hi,

I’m having a strange behaviour when merging together big trees (with complex structure). I cannot reproduce the problem with smaller trees and/or simpler structures, so I cannot give a running example, sorry. Any ideas or suggestions are welcome, though.

When merging several big trees (285) the output file automatically splits into 5 files 1.9GB each. When reading back the files, everything is OK for the 4 first files, but in the last file, and only for one particular branch of the last file, which contains a TClonesArrray of TRef, pointers are lost when trying to read the objects:

Error: illegal pointer to class object b 0x0 1214

I know that TRef are very special objects (also TClonesArrays). Is there a particular thing I need to worry about when merging trees with TRef? I am simply doing

TChain ch(“T”);
ch.Add("*.root");
ch.Merge(“all.root”);

and then quit root. Any ideas? Thanks!

PS: This is ROOT 4.00/08 on linux.

2

Could you try:

Long64_t maxsize = 100000000; //100GB maxsize *= 100; //to bypass some compiler limitations with big constants TTree::SetMaxTreeSize(maxsize); TChain ch("T"); ch.Add("*.root"); ch.Merge("all.root",0,"keep fast");
or simply use the standard tool hadd to merge ROOT files

hadd -f all.root *.root
Rene

3

Rene,

Thank you for the suggestion. I still get the same problem, though. I will get around without merging the trees. It’s not a big deal. It is just funny that I can perfectly access all the information on the file, but the TRef point nowhere (and this only happen for the last entries of the tree).

Thanks anyway,
Carlos

4

To make progress with this case, we will need access to the smallest possible set of files and a script reproducing the problem.

Rene