pitrou commented on code in PR #197:
URL: https://github.com/apache/parquet-format/pull/197#discussion_r1313375622
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src/main/thrift/parquet.thrift:
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@@ -191,6 +191,74 @@ enum FieldRepetitionType {
REPEATED = 2;
}
+/**
+ * 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 times 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 if max_definition_level is 0 or 1.
Review Comment:
Is it really important to save a bit of metadata size if there are two
definition levels? Special cases like this generally makes implementing the
spec more cumbersome. This is not a bean-counting contest.
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