voonhous commented on code in PR #20458:
URL: https://github.com/apache/hudi/pull/20458#discussion_r4462705628
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hudi-spark-datasource/hudi-spark-common/src/main/scala/org/apache/spark/sql/HoodieSparkTypeUtils.scala:
##########
@@ -37,16 +37,29 @@ object HoodieSparkTypeUtils {
def isCastPreservingOrdering(from: DataType, to: DataType): Boolean =
(from, to) match {
// NOTE: Casting between String and Numeric types re-orders elements
(for ex, "10" < "9"
- // lexicographically)
- case (StringType, _: NumericType) => false
- case (_: NumericType, StringType) => false
+ // lexicographically). These match by type, so that collated
strings on Spark 4 are
+ // rejected as well
+ case (_: StringType, _: NumericType) => false
+ case (_: NumericType, _: StringType) => false
// NOTE: Timestamps format in the session time zone, so local time
repeats across a DST
// fall-back (for ex, 01:30 EDT is followed by 01:10 EST) and the
strings re-order
- case (TimestampType, StringType) => false
+ case (TimestampType, _: StringType) => false
+ // NOTE: On Spark 4 StringType carries a collation, and casting to a
different collation changes
+ // the sort order (for ex, "B" < "a" in UTF8_BINARY but "a" < "B"
in UTF8_LCASE). Equality
+ // also compares the char/varchar length constraint, so those
casts are conservatively
+ // rejected too. On Spark 3 StringType is a singleton, making this
arm trivially true
+ case (fromStr: StringType, toStr: StringType) => fromStr == toStr
Review Comment:
Not reachable today: Hudi rejects collated string columns at schema
conversion, so `CREATE TABLE ... name STRING COLLATE UTF8_LCASE USING hudi` and
a DataFrame write with a collated column both fail before any stats are written:
```
IncompatibleSchemaException: Unexpected Spark DataType:
StringType(UTF8_LCASE)
at HoodieSparkSchemaConverters.toHoodieTypeNested
```
The mechanism is real though: Spark 4.1 still hands `col = 'a'` on a
collated column to `HoodieFileIndex`, so data skipping needs a collation guard
before the converter accepts collations. Added that to the #19445 checklist.
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