[GitHub] [parquet-format] gszadovszky commented on a diff in pull request #196: PARQUET-2249: Add nan_count to handle NaNs in statistics

["gszadovszky (via GitHub)" <gi...@apache.org>]

gszadovszky commented on code in PR #196:
URL: https://github.com/apache/parquet-format/pull/196#discussion_r1237651846


##########
src/main/thrift/parquet.thrift:
##########
@@ -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:
   I would vote on (1) because it would not store redundant data. I think `nan_pages` is not necessary. Meanwhile, we have to take care of the [boundary_order](https://github.com/apache/parquet-format/blob/master/src/main/thrift/parquet.thrift#L976) as well. Since no total ordering is defined `boundary_order` shall not be either `ASCENDING` or `DESCENDING` if there is any NaN page.



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