wgtmac commented on code in PR #242:
URL: https://github.com/apache/parquet-format/pull/242#discussion_r1603555087


##########
README.md:
##########
@@ -113,6 +119,55 @@ chunks they are interested in.  The columns chunks should 
then be read sequentia
 
  ![File 
Layout](https://raw.github.com/apache/parquet-format/master/doc/images/FileLayout.gif)
 
+### Parquet 3
+
+Parquet 3 files have the following overall structure:
+
+```
+4-byte magic number "PAR1"
+4-byte magic number "PAR3"
+8-byte offset of File Metadata v3
+8-byte length of File Metadata v3

Review Comment:
   +1.
   
   Use header to store file-level metadata prohibits streaming write, 
especially when extending parquet to be appendable. For example, 
implementations can choose to append new row groups to an existing parquet file 
by simply generating a new FileMetaData containing both old and new row groups.



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