JFinis commented on code in PR #196:
URL: https://github.com/apache/parquet-format/pull/196#discussion_r1243910046
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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:
> your idea sounds good but it is not that easy, unfortunately. Since no
total ordering is specified NaN values can get before negative infinity or
after positive infinity. An implementation that currently writes NaN values to
column indexes will break in this scenario.
@gszadovszky I don't fully understand your argument here. We just want to
make sure that a legacy reader who doesn't know the new semantics yet will
definitly *never filter* an only-NaN page. By using min=-Infinity and
max=Infinity, we basically write bounds that are as maximal as they can get, so
no legacy implementation should ever filter this page, which is the goal for
correctness.
Could you elaborate how you think an implementation would break? Maybe with
an example?
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