pitrou commented on code in PR #196:
URL: https://github.com/apache/parquet-format/pull/196#discussion_r1243478036
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src/main/thrift/parquet.thrift:
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@@ -966,6 +985,23 @@ struct ColumnIndex {
/** A list containing the number of null values for each page **/
5: optional list<i64> null_counts
+
+ /**
+ * A list of Boolean values to determine pages that contain only NaNs. Only
+ * present for columns of type FLOAT and DOUBLE. If true, all non-null
+ * values in a page are NaN. Writers are suggested to set the corresponding
+ * entries in min_values and max_values to NaN, so that all lists have the
same
+ * length and contain valid values. If false, then either all values in the
+ * page are null or there is at least one non-null non-NaN value in the page.
+ * As readers are supposed to ignore all NaN values in bounds, legacy readers
+ * who do not consider nan_pages yet are still able to use the column index
+ * but are not able to skip only-NaN pages.
+ */
+ 6: optional list<bool> nan_pages
Review Comment:
> Since no total ordering is defined `boundary_order` shall not be either
`ASCENDING` or `DESCENDING` if there is any NaN page.
Hmm. I am not theoretically against this (as is: the underlying concern is
reasonable), but I'm worried that some corners of the Parquet format are more
and more becoming a smattering of special cases that implementations must be
extra careful to implement correctly.
That said, it should also be easy for an implementation to entirely ignore
`boundary_order`, and instead detect any existing ordering from the
`min_values` and `max_values` (this should be fast given that there is one
value per page). It might even be useful to deprecate `boundary_order` and
encourage implementations to derive the information themselves?
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