emkornfield commented on code in PR #250:
URL: https://github.com/apache/parquet-format/pull/250#discussion_r1621089084
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src/main/thrift/parquet.thrift:
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@@ -1115,6 +1189,34 @@ union EncryptionAlgorithm {
2: AesGcmCtrV1 AES_GCM_CTR_V1
}
+/**
+ * Embedded metadata page.
+ *
+ * A metadata page is a data page used to store metadata about
+ * the data stored in the file. This is a key feature of PAR3
+ * footers which allow for deferred decoding of metadata.
+ *
+ * For common use cases the current recommendation is to use a
+ * an encoding that supported random access but implementations may choose
+ * other configuration parameters if necessary. Implementations
+ * SHOULD consider allowing configurability per page to allow for end-users
+ * to optimize size vs compute trade-offs that make sense for their use-case.
+ *
+ * Statistics for Metadata pages SHOULD NOT be written.
+ *
+ * Structs of this type should never be written in PAR1.
+ */
+struct MetadataPage {
+ // A serialized page including metadata thrift header and data.
+ 1: required binary page
+ // Optional compression applied to the page.
+ 2: optional CompressionCodec compression
Review Comment:
I think column data is at least 20 bytes per column? this means we get to
~1kb at 50 column and 4kb at at ~200 which I don't think are unreasonable.
What the relative compressibility is metadata is an open question. I will try
to measure this for wider schemas. For smaller structures that use this I
think the default would be not to compress.
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