emkornfield commented on code in PR #250:
URL: https://github.com/apache/parquet-format/pull/250#discussion_r1621091946
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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
+ // Number of elements stored. This is duplicated here to help in
+ // use-cases where knowing the total number of elements up front for
+ // computation would be useful.
+ 3: num_values
Review Comment:
For fixed width types PLAIN encoding gives us this data.
For variable width types, I wanted to solve this in a more general way with
the RANDOM_ACCESS_BYTE_ARRAY so that users could choose this to allow for
random access. In future iterations when we tackle improving for "point
lookup" use cases I imagine that would also help or be another option.
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