JFinis commented on code in PR #196:
URL: https://github.com/apache/parquet-format/pull/196#discussion_r1243710422
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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:
@pitrou That shouldn't be a problem. That's why this approach would require
alternative (2) or (3). In these alternatives nan_pages / value_counts would be
used to find only-NaN pages. If these indicate that the page is only NaN, the
min/max can be ignored and a reader can assume that the only values in the page
are NaNs. Old readers who don't understand these new fields yet would treat the
page simply as "maximum value range; cannot filter".
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