[ET Trac] [Einstein Toolkit] #1584: CarpetIOHDF5 should support extensible datasets

[Einstein Toolkit]

#1584: CarpetIOHDF5 should support extensible datasets
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 Reporter:  hinder       |       Owner:  eschnett           
     Type:  enhancement  |      Status:  new                
 Priority:  minor        |   Milestone:                     
Component:  Carpet       |     Version:  development version
 Keywords:               |  
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 Currently, CarpetIOHDF5 outputs one dataset per iteration.  This makes
 sense for gridfunctions, as the datasets are typically large and can
 change shape if there is regridding.  However, for grid arrays, the size
 is fixed from one iteration to the next, and there are often only a few
 values of interest. This means that output consists of hundreds of
 separate datasets, all of the same shape, and each with only a handful of
 elements.

 HDF5 supports "extensible datasets"
 <http://www.hdfgroup.org/HDF5/Tutor/extend.html>.  These are datasets
 which can be extended with new data in some directions after being first
 created.  I propose that CarpetIOHDF5 should support output of grid arrays
 using this format.  Multipole already does this.  We would add a dimension
 for "iteration" and extend the dataset in that dimension when new output
 is available.  This would mean that a grid array could be read from a
 single dataset, rather than having to loop over all iterations.

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Ticket URL: <https://trac.einsteintoolkit.org/ticket/1584>
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