anoopj commented on code in PR #18585:
URL: https://github.com/apache/iceberg/pull/18585#discussion_r4343060091
##########
format/spec.md:
##########
@@ -1008,15 +1007,30 @@ For example, stats for an optional `geometry` field
named `location` with field-
10_816: optional double z;
10_817: optional double m;
}
- 10_804: optional long value_count;
- 10_805: optional long null_value_count;
- 10_807: optional long total_bytes;
- // tight_bounds and nan_value_count are omitted for geo types
+ 10_803: optional long value_count;
+ 10_804: optional long null_value_count;
+ 10_806: optional long total_bytes;
+ // nan_value_count is omitted for geo types
}
```
For `variant`, both bounds are unshredded `variant` that store variant field
bounds by normalized JSON paths as field names. See [Bounds for
Variant](#bounds-for-variant) for details on producing these bounds.
+###### Stats Tightness
+
+Statistics are _tight_ when the bounds, `null_value_count`, and
`nan_value_count` are exact for the live rows of a file:
+
+* `lower_bound` and `upper_bound` for fixed-length types are equal to the
minimum and maximum of the live values.
+* `null_value_count` and `nan_value_count` are the counts across the live rows.
+
+Bounds for `string` and `binary` are never tight because they may be truncated
when written. Bounds for `geometry` and `geography` are a bounding box, not
exact minimum and maximum values.
Review Comment:
Added the qualifying phrase.
Geo - they are never tight like string/binary bounds. Clarified that as
well.
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