Re: [ROOT] TFolder or TDirectory?

From: Rene Brun (Rene.Brun@cern.ch)
Date: Sat Jan 12 2002 - 21:37:57 MET


Hi Christian,

Considering that the update frequency is very low: only a few hundred
times per week, and that the total size of the information is also
very small (you said about 20,000 employes: considering 100 bytes
per employee, this makes around 2 MBytes), I would recommend
 - to use the TFolder structure in memory with the hierarchy
   as you described it in your original mail.
 - to write the top folder with folder->Write at each transaction
   as a new key in the same file or in a different file.

The time for one transaction should be below 1 second.

Rene Brun

On Sat, 12 Jan 2002, cstrato@EUnet.at wrote:

> Dear Rene
> 
> Thank you for your reply, here is what I intend to do:
> I want to create a TFile, which should organize experiments in a
> hierarchical structure. The “employee” folder should contain references
> to TTrees and some additional information as objects. The TTrees
> themselfs containing the data will be stored in different TFiles.
> Access to the TTrees should be handled from this main file.
> The update frequency is low, e.g. hundred experiments per week each
> containing about hundred TTrees.
> 
> Although some of your slides suggest MySQL as Run/File catalog for
> the Event Store I must admit that I do not believe in RDBMS.
> Browsing the book “The Object Data Standard: ODMG 3.0” from the
> members of the ODMG, one can see that most classes described in the
> book are already implemented in ROOT. One of the few classes missing
> is class TTransaction {begin(), commit(), abort()}.
> I have already started  to implement this class in a way which is
> sufficient
> for my purposes, and it seems to work fine.
> 
> My main problem is to implement a hierarchical structure in the main
> file which is not only browsable but also searchable.
> 
> Best regards
> Christian
> 
> 
> Rene Brun wrote:
> 
> > Hi Christian,
> >
> > It is difficult to give you an advice without knowing a more
> > precise configuration and access patterns.
> >  What is the update frequency? one per millisecond, second, month ?
> >  What is the real population in each node?
> >
> > It is also not clear to me what are the operations you need to
> > perform: in memory only, on disk only, on both.
> >
> > ROOT I/O is not an alternative to a pure conventional relational
> > data base to describe eg, employee/organisation type of relations.
> > May be a tool like MySQL is more adapted to this task.
> >
> > Rene Brun
> >
> > On Sun, 6 Jan 2002, cstrato@EUnet.at wrote:
> >
> > > Dear Rooters!
> > >
> > > Maybe you can give me some advice whether to use TFolder or TDirectory
> > > when storing large amounts of TObjects in a TFile.
> >
> > >
> > > Thank you in advance
> > >
> > > Best regards
> > > Christian
> > > ----------------------------------
> > > C.h.r.i.s.t.i.a.n  S.t.r.a.t.o.w.a
> > > V.i.e.n.n.a,  A.u.s.t.r.i.a
> > >
> > >
> 



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