wgtmac commented on code in PR #250:
URL: https://github.com/apache/parquet-format/pull/250#discussion_r1621567333


##########
README.md:
##########
@@ -118,6 +118,51 @@ 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)
 
+ ### PAR3 File Footers
+
+ PAR3 file footer footer format designed to better support wider-schemas and 
more control
+ over the various footer size vs compute trade-offs.  Its format is as follows:
+   - Serialized Thrift FileMetadata Structure
+   - (Optional) 4 byte CRC32 of the serialized Thrift FileMetadata.
+   - 4-byte length in bytes (little endian) of all preceding elements in the 
footer.
+   - 4-byte little-endian flag field to indicate features that require special 
parsing of the footer.
+     Readers MUST raise an error if there is an unrecognized flag.  Current 
flags:
+
+     * 0x01 - Footer encryption enabled (when set the encryption information 
is written before 
+        FileMeta structure as in the PAR1 footer).
+     * 0x02 - CRC32 of FileMetadata Footer.

Review Comment:
   I was thinking to leverage the features flag to continue the effort in 
https://github.com/apache/parquet-format/pull/164 which defines core features 
that the parquet file implements.



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