Re: Chain or tree?

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
>>
>>
>
>
>
>
Received on Thu Oct 25 2007 - 15:13:00 CEST