JFinis commented on code in PR #196:
URL: https://github.com/apache/parquet-format/pull/196#discussion_r1242530201
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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:
@mapleFU From just reading the spec, I don't think we should have a backward
compatibility problem, as legacy readers are already compelled to ignore NaNs
if they find them anywhere. Thus, a legacy reader would ignore the NaN it finds
in the column index and just not filter that page.
Also note that regardless of whether we do (1), (2), or (3) [we basically
**have to** write NaN into min and
max](https://github.com/apache/parquet-format/pull/196#issuecomment-1491890773).
We have to write a valid value and every value except NaN would simply be
wrong, if a page contains only NaNs. The approaches would just differ in what
we write **in addition**, so to a legacy reader that wouldn't read anything new
fields, the three approaches would be equal.
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