rdblue commented on code in PR #18604:
URL: https://github.com/apache/iceberg/pull/18604#discussion_r4461921050
##########
core/src/main/java/org/apache/iceberg/StatsUtil.java:
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@@ -325,4 +336,194 @@ private static boolean isScalar(Schema schema,
Map<Integer, Integer> parentIndex
return true;
}
+
+ /**
+ * Lower and upper bounds for source values in a partition from an
order-preserving transform.
+ *
+ * <p>Every source value that transforms to the partition is >= lower and <=
upper. Upper is null
+ * when unbounded. Both bounds are inclusive.
+ *
+ * <p>For most transforms, lower and upper are the values in the partition.
Exceptions:
+ *
+ * <ul>
+ * <li>For string and binary truncate, upper is the next prefix when it
exists, so upper can
+ * truncate to the next partition. That still covers every value that
truncates to the
+ * partition.
+ * <li>For time transforms, lower starts one unit earlier when the
partition value is <= 1970 to
+ * handle older writers that rounded pre-1970 values toward zero.
Review Comment:
Would be nice to link to the issue or PR. I'm familiar with the problem that
was fixed and I'm not quite sure what "older writers rounded pre-1970 values
toward 0" quite means. It wasn't rounding, it was a correctness bug in the
calculation.
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