JFinis commented on code in PR #196:
URL: https://github.com/apache/parquet-format/pull/196#discussion_r1146095493
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README.md:
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@@ -163,18 +163,25 @@ following rules:
[Thrift definition](src/main/thrift/parquet.thrift) in the
`ColumnOrder` union. They are summarized here but the Thrift definition
is considered authoritative:
- * NaNs should not be written to min or max statistics fields.
- * If the computed max value is zero (whether negative or positive),
- `+0.0` should be written into the max statistics field.
- * If the computed min value is zero (whether negative or positive),
- `-0.0` should be written into the min statistics field.
-
- For backwards compatibility when reading files:
- * If the min is a NaN, it should be ignored.
- * If the max is a NaN, it should be ignored.
- * If the min is +0, the row group may contain -0 values as well.
- * If the max is -0, the row group may contain +0 values as well.
- * When looking for NaN values, min and max should be ignored.
+ * The following compatibility rules should be applied when reading
statistics:
+ * If the nan_count field is set to > 0 and both min and max are
Review Comment:
TBH: I would actually love to have a `num_values` list in the column index.
We have the same in the statistics, Iceberg does the same, and not needing
min=max=NaN for only-NaN checking would actually be much more elegant IMHO.
I just didn't want to suggest adding another list to each column index for
the added space cost. However, given that these indexes are negligibly small in
comparison to the data, I think actually no one would mind that extra space. If
the consensus is that this is preferrable, I'm happy to adapt the commit to
that.
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