Baunsgaard commented on PR #1697:
URL: https://github.com/apache/systemds/pull/1697#issuecomment-1250334572

   I was thinking of the index-block design used in binary, but since the 
compression framework compress an entire matrix in CP i would have to decompose 
the compression into multiple blocks if we want this and, in CP, reading would 
have to combine them again. 
   
   I think this overcomplicate things unless we somehow make the compression 
able to combine different blocks with the same compression plan. 
   
   Furthermore if we write a compressed distributed block-indexed matrix to 
disk we get multiple blocks with different formats that would not be able to 
combine nicely in CP anyway. Enforcing that such a read should lead to SP 
instructions.
   
   In the end the problems make reading and writing the same way as binary 
blocks a bit challenging especially if you want same behavior.
   But i can suggest we always treat the compressed format as an index-block 
based file with a block size >= nCols && nRows ;)
   


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