JFinis commented on code in PR #196:
URL: https://github.com/apache/parquet-format/pull/196#discussion_r1146080282
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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:
To this suggestion:
> Seems it's a little strict here? Just ingore min-max seems ok?
Note that the line you mentioned here just tells a reader that they *can*
rely on this information, and therfore could, e.g., skip this page if a
predicate like `x = 12.34` was used. They can of course also opt to ignore this
information and not skip but rather scan the page. If we removed this, a reader
couldn't do the skip here.
I guess this is related to your general suggestion: How do we detect
only-NaN pages? Depending on what we do for that, this line will be adapted
accordingly.
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