Re: Chain or tree?

Hi all,

    I have used trees up to 25 GB without any problem - they are fast, efficient and easy to manage.

    Dimitri

-- 
        _/_/_/                             _/_/_/
       _/    _/   Dimitri  BOURILKOV      _/    _/
      _/    _/   University of Florida   _/_/_/
     _/    _/   bourilkov_at_phys.ufl.edu  _/    _/
    _/_/_/                             _/_/_/

Rene Brun wrote:


> Elemer,

> 

> The defaut maximum size for a Tree is 1.9 GBytes.

> ROOT can support Trees as large as you want providing your OS can manage 

> it and your disk is large enough.

> To change the default max value, call the static function 

> TTree::SetMaxTreeSize.

>    Long64_t maxTreeSize = 1000000000*100; //max size set to 100 GBytes

>    TTree::SetMaxTreeSize(maxtreeSize);

> Now all the Trees that you create can reach 100 GBytes.

> 

> Rene Brun

> 

> 

> Elemer Nagy wrote:

> 

>> Is it possible at all to have one single Tree of 1 TeraByte?
>> I thought the size of a Tree was limited to 2 Gbyte.
>>
>> Elemer
>>
>>
>> On Thu, 25 Oct 2007, Rene Brun wrote:
>>
>> Chiara,
>>
>> Let me put this way ::)
>> -It is better to have one single Tree of 1 GByte than a TChain of 1000 
>> files
>> with a 1 Mbyte Tree.
>> -It is better to have one TChain with 1000 files with a 1GByte Tree in 
>> each than
>> one single Tree of 1 TeraByte.
>>
>> Larger the Tree, larger the internal tables to address the Tree baskets.
>> Anyhow the overhead indiced by a TChain should be very small 
>> (opening/closing
>> files),
>> TChain has many advantages in case you want to parallelize the 
>> processing. The
>> individual files
>> can be on different nodes. You do not need a gigantic Tree on one 
>> single node
>> that will generate
>> I/O bottlenecks, etc.
>>
>> Rene Brun
>>
>> Chiara Zampolli wrote:
>>  
>>
>>> Dear all,
>>>
>>>    I was wondering whether there is a difference in performance (memory,
>>> mainly), in case one chains some trees written on files using a 
>>> TChain, or
>>> building a TTree with CopyEntries. I have tried to see what happens 
>>> using
>>> gSystem->GetMemInfo(), and also with "top", but it seems as if 
>>> there's no
>>> difference.... Am I wrong? BTW, which is the "best" solution?
>>>
>>>     Thanks in advance. Cheers,
>>>                         Chiara
>>>