Re: Cloning trees with TChain: drastic performance loss

Hi Alexander,

Not really. The 1st one is (in this case) just a thin wrapper around the 2nd one.

Cheers,
Philippe.

On 5/16/11 11:27 AM, Alexander Mann wrote:
>
> Hi Philippe,
>
> oh, indeed, thanks for spotting this!
>
> Is one of those variants
>
> > collChain->GetEntry(jentry);
> > collChain->GetTree()->GetEntry(ientry);
>
> recommended over the other?
>
> cu,
> Alexander
>
>
> On 05/16/2011 06:06 PM, Philippe Canal wrote:
>> Hi Alexander,
>>
>> Instead of
>>
>> Long64_t ientry = collChain->LoadTree(jentry);
>> collChain->GetEntry(ientry);
>>
>> you meant:
>>
>> Long64_t ientry = collChain->LoadTree(jentry);
>> collChain->GetEntry(jentry);
>>
>> or
>>
>> Long64_t ientry = collChain->LoadTree(jentry);
>> collChain->GetTree()->GetEntry(ientry);
>>
>> The value returned by LoadTree is the entry number within the current
>> TTree and
>> must be used only on the TBranch object or on the underlying TTree.
>>
>> The code as-is is not only slow but also only look at the data in the
>> first TTree.
>>
>> Cheers,
>> Philippe.
>>
>> On 5/16/11 10:58 AM, Alexander Mann wrote:
>>>
>>> Hi Philippe,
>>>
>>> I don't see anything that could trigger such a behaviour, but maybe I
>>> am missing something. This is the main loop of my code:
>>>
>>> // connect branches
>>> TBranch *b_runno;
>>> collChain->SetBranchAddress("RunNumber", &runno, &b_runno);
>>> TBranch *b_evno;
>>> collChain->SetBranchAddress("EventNumber", &evno, &b_evno);
>>>
>>> //Create a new file + a clone of old tree in new file
>>> TFile *newfile = new TFile(outFile.c_str(), "recreate");
>>> TTree *newtree = collChain->CloneTree(0);
>>>
>>> // do cloning
>>> time_t stimee = time(NULL);
>>> cout << "Start cloning tree at " << stimee << "..." << endl;
>>> long stepsize = nentries / 100;
>>> long stepleft = stepsize;
>>> long evwritten = 0;
>>> for (Long64_t jentry = 0; jentry < nentries; ++jentry) {
>>> stepleft = 1;
>>> if (--stepleft == 0) {
>>> stepleft = stepsize;
>>> cout << jentry << "/" << nentries << " (" << evwritten << ", " <<
>>> currtime() << ")\r";
>>> fflush(stdout);
>>> }
>>> Long64_t ientry = collChain->LoadTree(jentry);
>>> collChain->GetEntry(ientry);
>>> if (vec_evnos[runno].find(evno) != vec_evnos[runno].end()) {
>>> newtree->Fill();
>>> ++evwritten;
>>> }
>>> }
>>> cout << endl;
>>>
>>> I am using ROOT 5.26.00e and running over quasi-local files. If you
>>> prefer I can send you a test case including the complete macro.
>>>
>>> cu,
>>> Alexander
>>>
>>>
>>> On 05/16/2011 05:46 PM, Philippe Canal wrote:
>>>> Hi Alexander,
>>>>
>>>> LoadTree should be most of the time 'immediate'. The behavior you
>>>> describe usually indicates that some other portion of the code is
>>>> directly or indirectly doing another call to LoadTree with a totally
>>>> different entry number
>>>> ( 0 or GetEntries()-1 are the most typical). This result is having to
>>>> open the file and load the TTree object every entry (and this is a
>>>> 'slow' operation).
>>>>
>>>> Cheers,
>>>> Philippe.
>>>>
>>>> On 5/16/11 10:41 AM, Alexander Mann wrote:
>>>>>
>>>>> Hi,
>>>>>
>>>>> I am using a slightly modified version of some standard ROOT example
>>>>> code from
>>>>>
>>>>> http://root.cern.ch/root/html/tutorials/tree/copytree3.C.html
>>>>>
>>>>> to skim TTrees. The main difference is that I am using TChain instead
>>>>> of TTree, and therefore I am using
>>>>>
>>>>> Long64_t ientry = collChain->LoadTree(jentry);
>>>>> collChain->GetEntry(ientry);
>>>>>
>>>>> This works fine, but after ~500 events (which is probably all from the
>>>>> first file in the TChain) the speed abruptly decreases from about 27
>>>>> events/s to 0.05 events/s, spent in equal parts in LoadTree and
>>>>> GetEntry as it seems.
>>>>>
>>>>> Is there something I can do about this?
>>>>>
>>>>> cu,
>>>>> Alexander
>>>>>
>>>
>
Received on Mon May 16 2011 - 21:00:20 CEST