pitrou commented on code in PR #185:
URL: https://github.com/apache/parquet-format/pull/185#discussion_r1041067303
##########
README.md:
##########
@@ -144,6 +144,38 @@ documented in [LogicalTypes.md][logical-types].
[logical-types]: LogicalTypes.md
+### Sort Order
+
+Parquet stores min/max statistics at several levels (e.g. RowGroup, Page Index,
+etc). Comparison for values of a type follow the following logic:
Review Comment:
```suggestion
Parquet stores min/max statistics at several levels (such as Column Chunk,
Column Index and Data Page). Comparison for values of a type obey the
following rules:
```
##########
README.md:
##########
@@ -144,6 +144,38 @@ documented in [LogicalTypes.md][logical-types].
[logical-types]: LogicalTypes.md
+### Sort Order
+
+Parquet stores min/max statistics at several levels (e.g. RowGroup, Page Index,
+etc). Comparison for values of a type follow the following logic:
+
+1. Each logical type has a specified comparison order. If a column is
+ annotated with an unknown logical type, statistics may not be used
+ for pruning data. The sort order for logical types is documented in
+ the [LogicalTypes.md][logical-types] page.
+2. For primitives the following sort orders apply:
+
+ * BOOLEAN - false, true
+ * INT32, INT64, FLOAT, DOUBLE - Signed comparison. Floating point values
are
+ not totally ordered due to special case like NaN. They require special
+ handling when reading statistics. The details are documented in
parquet.thrift in the
+ `ColumnOrder` union. They are summarized
Review Comment:
Need to synchronize this with the final wording from `parquet.thrift`.
##########
README.md:
##########
@@ -144,6 +144,38 @@ documented in [LogicalTypes.md][logical-types].
[logical-types]: LogicalTypes.md
+### Sort Order
+
+Parquet stores min/max statistics at several levels (e.g. RowGroup, Page Index,
+etc). Comparison for values of a type follow the following logic:
+
+1. Each logical type has a specified comparison order. If a column is
+ annotated with an unknown logical type, statistics may not be used
+ for pruning data. The sort order for logical types is documented in
+ the [LogicalTypes.md][logical-types] page.
+2. For primitives the following sort orders apply:
Review Comment:
```suggestion
2. For primitive types, the following rules apply:
```
##########
src/main/thrift/parquet.thrift:
##########
@@ -902,6 +902,13 @@ union ColumnOrder {
* - 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.
+ *
+ * When writing statistics the following rules should be followed:
+ * - NaNs should not be written to min or max statistics fields.
+ * - Only -0 should be written into min statistics fields (if only
+ * +0 is present in the column it should be converted to -0.0).
+ * - Only +0 should be written into a max statistics fields (if
+ * only -0 is present it must be convereted to +0).
Review Comment:
Suggestion to make wording clearer.
```suggestion
* - 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.
```
##########
README.md:
##########
@@ -144,6 +144,38 @@ documented in [LogicalTypes.md][logical-types].
[logical-types]: LogicalTypes.md
+### Sort Order
+
+Parquet stores min/max statistics at several levels (e.g. RowGroup, Page Index,
+etc). Comparison for values of a type follow the following logic:
+
+1. Each logical type has a specified comparison order. If a column is
+ annotated with an unknown logical type, statistics may not be used
+ for pruning data. The sort order for logical types is documented in
+ the [LogicalTypes.md][logical-types] page.
+2. For primitives the following sort orders apply:
+
+ * BOOLEAN - false, true
+ * INT32, INT64, FLOAT, DOUBLE - Signed comparison. Floating point values
are
Review Comment:
I would suggest making a separate list item for floating-point:
```suggestion
* INT32, INT64 - Signed comparison.
* FLOAT, DOUBLE - Signed comparison with special handling of NaNs
and signed zeros. The details are documented in...
```
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