wgtmac commented on issue #50622:
URL: https://github.com/apache/arrow/issues/50622#issuecomment-5065701101

   > unsigned Arrow storage can never round trip (Arrow Uint -> Parquet INT -> 
Arrow Int)
   
   I think this is possible. I'm not familiar with arrow-rs. For arrow-cpp, the 
Parquet writer serializes the Arrow schema into footer when the writer property 
`store_schema` is enabled (which is the default value) and then Parquet reader 
deserializes that schema to restore their original form on read.
   
   > Null -> Null: the shredding table has no null row
   
   This is a good argument. Parquet indeed has a UNKNOWN logical type to 
represent a column with no known type. It would be useful when user-hinted 
column cannot be shredded. So it seems like a missing piece in the Parquet 
shredding spec?
   
   cc @zeroshade @alamb 


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