asolimando commented on PR #24027:
URL: https://github.com/apache/datafusion/pull/24027#issuecomment-5191584458

   > This looks good to me overall, just one small test comment.
   > 
   > I'm not sure I fully understand the existing behavior that always 
downgrades non-primitive schemas to inexact, but I also recall that it doesn't 
make a huge difference.
   
   Hey Adam, my understanding is that non-primitive types (composite types, 
arrays, list, maps) contribute a varying amount of bytes, depending on the size 
of the collection, which cannot be really known, so it's inexact by nature.
   
   Primitive types, on the contrary, are tied to a fixed byte-size which can be 
computed exactly (so given a schema composed only by primitive types, you can 
tell how many bytes a single row takes, and total byte size is row byte size 
times number of rows).


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