Re: [PR] [Variant] Preserve `UUID` extension type metadata for Parquet writer [arrow-rs]

["alamb (via GitHub)" <gi...@apache.org>]

alamb commented on code in PR #10015:
URL: https://github.com/apache/arrow-rs/pull/10015#discussion_r3348885650


##########
parquet-variant-compute/src/variant_array.rs:
##########
@@ -868,6 +868,20 @@ impl TryFrom<&StructArray> for ShreddingState {
     }
 }
 
+/// Build the `typed_value` [`FieldRef`] for a shredded column.
+///
+/// The Variant spec maps `FixedSizeBinary(16)` exclusively to UUID, so any

Review Comment:
   can you add a reference to this part of the spec?



##########
parquet-variant-compute/src/variant_array.rs:
##########
@@ -868,6 +868,20 @@ impl TryFrom<&StructArray> for ShreddingState {
     }
 }
 
+/// Build the `typed_value` [`FieldRef`] for a shredded column.
+///
+/// The Variant spec maps `FixedSizeBinary(16)` exclusively to UUID, so any

Review Comment:
   https://parquet.apache.org/docs/file-format/types/variantshredding/ says
   
   > Shredded values must use the following Parquet types:
   
   
   Variant Type | Parquet Physical Type | Parquet Logical Type
   -- | -- | --
   ... | ... | ...
   uuid | FIXED_LEN_BYTE_ARRAY[len=16] | UUID
   
   
   But I didn't see it say the other way around that any FIXED_LEN_BYTE_ARRAY was always UUID 🤔 
   
   



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