[GitHub] [incubator-iceberg] aokolnychyi commented on a change in pull request #135: Use big-endian byte order for UUIDs in Conversions

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aokolnychyi commented on a change in pull request #135: Use big-endian byte order for UUIDs in Conversions
URL: https://github.com/apache/incubator-iceberg/pull/135#discussion_r267127649
 
 

 ##########
 File path: api/src/main/java/com/netflix/iceberg/types/Conversions.java
 ##########
 @@ -98,7 +99,7 @@ public static ByteBuffer toByteBuffer(Type type, Object value) {
         }
       case UUID:
         UUID uuid = (UUID) value;
-        return ByteBuffer.allocate(16).order(ByteOrder.LITTLE_ENDIAN)
+        return ByteBuffer.allocate(16).order(ByteOrder.BIG_ENDIAN)
 
 Review comment:
   @rdblue I am afraid the order is correct but indices are not.
   
   Here is an example I tested:
   
   ```
   UUID randomUUID = UUID.randomUUID();
   System.out.println(randomUUID.toString());
   // abcc5e8d-81f3-4ea2-b624-a14ce8c513b9
   ByteBuffer buffer = Conversions.toByteBuffer(UUIDType.get(), randomUUID);
   Object value = Conversions.fromByteBuffer(UUIDType.get(), buffer);
   System.out.println(value);
   // abb624a1-4ce8-c513-b900-000000000000
   ```
   
   So the logic in `toByteBuffer` should really be:
   
   ```
         case UUID:
           UUID uuid = (UUID) value;
           return ByteBuffer.allocate(16).order(ByteOrder.BIG_ENDIAN)
               .putLong(0, uuid.getMostSignificantBits())
               .putLong(8, uuid.getLeastSignificantBits());
   ```
   
   The test that I added passes because UUIDs are represented as `fixed[16]` in Parquet and we invoke only `fromByteBuffer` in this case.
   
   Do we want to have a separate suite for `Conversions`?

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