jiwen624 commented on code in PR #57272:
URL: https://github.com/apache/spark/pull/57272#discussion_r3591157939
##########
sql/catalyst/src/main/java/org/apache/spark/sql/catalyst/expressions/CollatedString.java:
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@@ -17,34 +17,37 @@
package org.apache.spark.sql.catalyst.expressions;
+import java.util.Arrays;
+
/**
* A DataSketches ItemsSketch item for non-binary collated strings
(SPARK-58069).
* <p>
* Equality and hashing are driven solely by the collation {@code key}, so
that collation-equal
* strings (e.g. {@code 'HELLO'} and {@code 'hello'} under {@code UTF8_LCASE})
are counted as a
* single item. The {@code original} field retains an actual input value to
return in the result,
* mirroring how {@code mode()} returns a real value rather than the
normalized collation key.
+ * <p>
+ * The {@code key} is the raw collation sort-key bytes (SPARK-58096). ICU sort
keys are arbitrary
+ * bytes, not valid UTF-8, so decoding them to a {@code String} is lossy: two
collation-distinct
+ * values whose keys differ only within invalid-byte regions would decode to
the same {@code String}
+ * and be incorrectly merged. Keying on the bytes directly avoids that
over-merge.
*/
public class CollatedString {
- private final String key;
+ private final byte[] key;
private final String original;
- public CollatedString(String key, String original) {
+ public CollatedString(byte[] key, String original) {
this.key = key;
this.original = original;
}
- public String key() {
Review Comment:
Dropped the unused key() accessor: nothing reads it, and exposing the raw
sort-key byte[] leads to a risk of it being mutated externally.
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