emkornfield commented on code in PR #197:
URL: https://github.com/apache/parquet-format/pull/197#discussion_r1150299027
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src/main/thrift/parquet.thrift:
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@@ -223,6 +223,17 @@ struct Statistics {
*/
5: optional binary max_value;
6: optional binary min_value;
+ /** The number of bytes the row/group or page would take if encoded with
plain-encoding */
+ 7: optional i64 plain_encoded_bytes;
+ /**
+ * When present there is expected to be one element corresponding to each
repetition (i.e. size=max repetition_leve)
+ * where each element represens the count of the number of times that
level occurs in the page/column chunk.
+ */
+ 8: optional list<i64> repetition_level_histogram;
Review Comment:
So some simple examples in from Arrow (my rep/def level calculations are
rusty so please double check to make sure they make sense):
1. If all you have are nested structures (say 3 nullable levels), then the
number of null values at the leaf is the sum of the first 3 elements of the
definition level histogram. Individual level nullability for Arrow isn't super
important because it always leaves the space for nulls so it is pretty much
square. You could however determine that there are no nulls at the second
level of nesting by checking the appropriate histogram box (and potentially
save the allocation of the bit vector in that case)
2. If you have two nested lists and assuming lists and elements are not
nullable. The number of inner nested lists is `rep_hist[0] - def_hist[0] +
{rep_hist[1]` (outer list starts - empty outer lists + inner list starts).
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