[ET Trac] [Einstein Toolkit] #1338: Rename Carpet output files

[Einstein Toolkit]

#1338: Rename Carpet output files
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  Reporter:  eschnett  |       Owner:  eschnett
      Type:  defect    |      Status:  new     
  Priority:  major     |   Milestone:          
 Component:  Carpet    |     Version:          
Resolution:            |    Keywords:          
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Comment (by hinder):

 Remember also that for multipatch data, the map is specified with an
 additional "." separator.  Whatever we decide, we must document it very
 clearly so that it is possible to modify analysis tools to do the right
 thing in every situation.  At the moment, the double-colon works on the
 vast majority of systems that are in active use with Carpet data. I agree
 it is not ideal, and that it should be possible to access and analyse
 Carpet data on Windows and using Windows file sharing, but unless the
 change is done carefully, this is going to cause immediate breakage and
 pain to existing tools and users, for a benefit which is likely small.
 So, if someone still wants to propose that the filename scheme is changed,
 please come up with a concrete proposal which addresses:

 1. ASCII
 2. HDF5
 3. Multipatch
 4. All currently-valid Cactus group and variable names
 5. One-file-per-group and one file per variable

 I had a look in the CarpetIOHDF5 source code, and couldn't find the
 function that constructs the filename; is this done at a higher level in
 Cactus or Carpet and then passed in to OutputVarAs?

 From looking at my simulations directory, it looks like the colon is only
 used when outputting one file per group, and in that case the double colon
 is used to separate an implementation name prefix from the group name.  Is
 that correct?

 Roland: I don't understand your "grid" example.  When would filenames like
 this be generated?  "grid" is the implementation, and the group is called
 "coordinates", so the current name would be
 "grid::coordinates.x.file_0.idx.h5", wouldn't it?  Is there another
 filename scheme where the variable name is used with the implementation
 name?

 Frank: Is it really true that you can have '-' or '.' in implementation
 and variable names?  Don't variable names have to be valid C and Fortran
 identifiers?    Maybe not implementation names.  We need to be able to
 distinguish between <variable> and <implementation>::<group>.  Since
 variables surely cannot have '-', it seems that <implementation>-<group>
 should be unambiguous.

 This issue would be less important if Cactus had a mechanism for writing a
 metadata file describing what had been output.  This could then be read by
 analysis tools, and they wouldn't have to guess from filenames.  I will
 open a ticket for this (I thought there was one already, but I can't find
 it).  This would not solve the problem completely, as any time the output
 is ambiguous, it would also be possible for there to be a collision
 between two different output filenames, but it would take the guesswork
 out of writing analysis tools.

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Ticket URL: <https://trac.einsteintoolkit.org/ticket/1338#comment:17>
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