[Octave-bug-tracker] [bug #55427] save -v7 exits with "error compressing data element"

[Philip Nienhuis]

Follow-up Comment #15, bug #55427 (project octave):

Using the 6.2.93 nightly from July 3, I tried "save -v7" with a bunch of large
data structures I have lying around on my laptop:

>> whos
Variables visible from the current scope:

variables in scope: top scope

   Attr Name        Size                     Bytes  Class
   ==== ====        ====                     =====  =====
        ans        95x1                        804  cell
        divers      1x148                158144931  struct
        gis         1x1                   55582705  struct
        gr          1x1                   65228745  struct

Total is 245 elements using 278957185 bytes


(ans = "fieldnames (gr)")
During "save -v7 test.mat divers gis gr" I got no errors (nice!) but after
loading the resulting 58 MB file in Matlab r2014a, I get:

>> whos
  Name         Size                 Bytes  Class     Attributes

  ans         95x1                  12248  cell                
  divers       1x148            158468902  struct              
  gis          1x1              213452354  struct              
  gr           1x1               81220402  struct              


where to my surprise some structs occupy much more memory (in bytes) than in
Octave.
I'd have to dive deeper into it to find out why (the deeply nested) structs
'gis' and 'gr' got blown up that much, but that'll be a lengthy affair I'm
afraid. Or maybe Octave is just much more memory-efficient?
(Running "pack" at the Matlab command line didn't change even just one byte of
the occupied memory sizes, as can be expected when loading a .mat file in a
pristine Matlab session.)

When I'm back I can try bigger struct arrays - at work we got some 140+ MB
.mat files created with Matlab using "-v7". It's those files with which I hit
this bug.


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