emkornfield commented on code in PR #197:
URL: https://github.com/apache/parquet-format/pull/197#discussion_r1301968222
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src/main/thrift/parquet.thrift:
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@@ -191,6 +191,62 @@ enum FieldRepetitionType {
REPEATED = 2;
}
+/**
+ * Tracks a histogram of repetition and definition levels for either a page
or column chunk.
+ *
+ * This is useful for:
+ * 1. Estimating the size of the data when materialized in memory
+ * 2. For filter push-down on nulls at various levels of nested structures
and
+ * list lengths.
+ */
+struct RepetitionDefinitionLevelHistogram {
+ /**
+ * When present there is expected to be one element corresponding to each
repetition (i.e. size=max repetition_level+1)
+ * where each element represents the number of time the repetition level
was observed in the data.
+ *
+ * This value should not be written if max_repetition_level is 0.
+ **/
+ 1: optional list<i64> repetition_level_histogram;
+ /**
+ * Same as repetition_level_histogram except for definition levels.
+ *
+ * This value should not be written when max_definition_level is 0.
+ **/
+ 2: optional list<i64> definition_level_histogram;
+ }
+
+/**
+ * A structure for capturing metadata for estimating the unencoded,
uncompressed size
+ * of data written. This is useful for readers to estimate how much memory is
needed
+ * to reconstruct data in their memory model and for fine grained filter
pushdown on nested
+ * structures (the histogram contained in this structure can help determine
the
+ * number of nulls at a particular nesting level).
+ *
+ * Writers should populate all fields in this struct except for the exceptions
listed per field.
+ */
+struct SizeEstimationStatistics {
Review Comment:
Values are exact. would SizeStatistics be more meaningful from you
perspective?
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