Re: ROOT file_ids and Bundle_ids

[Arie Shoshani <arie@math.lbl.gov>]

>    DMM:
> 
>    I expressed my concerns last month about faking Objectivity into 
>    generating db numbers as fileids for ROOT files, and I thought that 
>    Doug and Torre, among others, shared my concerns.  By the way, 
>    implementing that deception may involve some subtleties.
> 
>    My understanding is that David Zimmerman is working on a method for 
>    generating consistent fileids for ROOT and Objectivity files, with 
>    a simple interface for use by Storage Manager components to translate 
>    from ids to names.  If he does not have time for this, I will volunteer 
>    to do it.

For MDC2, it does not matter to the Storage Manager how file_ids are 
assigned, only that they are 16 bit file_ids (similar to the Objectivity 
file_ids).  The actual file_name is needed by the cache manager and as long 
as it has some way of getting it, that's OK.  So, your plan is fine as long 
as there is a way to get file_names from file_ids.


> >  2)  All file names (including path_names if more that a single 
> >  directory is used) will be retrieved from the Objectivity catalog.
> >  
> 
>    DMM:
> 
>    I would be happier if we could amend this to say "will be retrieved 
>    from the Objectivity federation."

That's fine.

 
> >  3)  We assume files can be in different directories.  However, the same 
> >  directory structure will exist beyond a root-path in HPSS as in Unix.
> >  (e.g. suppose the Objectivity root-path is o1/o2/o3 and HPSS root-path 
is 
> >  h1/h2, then a file in Objectivity directory o1/o2/03/x/y/z/file_name, 
> >  will be in the HPSS directory as h1/h2/x/y/z/file_name.)  Thus, given 
the 
> >  objectivity path, the HPSS path can be generated.
> >  
> 
>    DMM:
> 
>    I'm not sure I understand this.  Do you mean that I can have an 
>    arbitrary number of prefix pairs:
> 
>    o1/o2/o3    corresponds to HPSS h1/h2
>    o1/o2/o4    corresponds to HPSS h1/h3
>    o1/o5/06    corresponds to HPSS h1/h4
>    o7/o8       corresponds to HPSS h5/h6/h7
>    ..., 
>  
>    or that I can have only one, so that the HPSS directory structure 
>    must (after substituting prefixes) precisely mirror the disk directory 
>    structure?

The latter is correct.  i.e. all prefixes uare the same and the Objectivity 
and HPSS subdirectories appended to the prefixes are the same.  Thus, if the 
prefix:  o1/o2/o3    corresponds to HPSS h1/h2,
Then files:
o1/o2/o3/x/file1    corresponds to HPSS h1/h2/x/file1,
o1/o2/o3/x/file2    corresponds to HPSS h1/h2/x/file2, etc.

(where x can be sunstituted with any subdirectory path.)

  
> >  4)  The QM will pass to the EI only the bundle_id and the set of 
> >  event_ids that qualify for this bundle.  The EI will return this 
> >  bundle_id when releasing the bundle.
> >  
> 
>    DMM:
> 
>    Can Alex or Henrik comment on this:  How difficult would it be for MDC2 
to 
>    support an interface that takes a bundle_id as input and returns the 
>    corresponding filelist (fileids or filenames)?  If this is done, I think 
>    I can live with the bundle_id approach for the OOI in MDC2.  

As Alex said: we can return file_ids for the bundle (or he can provide an
interface so the EI can get it), but the key point is that we need a unique 
though temporary) id for the bundle returned to the QM when the EI is done 
with that bundle.

Let us know how you decide to proceed with ROOT file_id assignment.

Thanks, Arie.