peterxcli commented on code in PR #4863:
URL: https://github.com/apache/datafusion-comet/pull/4863#discussion_r3546228635
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spark/src/main/scala/org/apache/comet/serde/maps.scala:
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@@ -75,8 +75,43 @@ object CometMapExtract extends
CometExpressionSerde[GetMapValue] {
}
}
+/**
+ * Shared support for the `spark.sql.mapKeyDedupPolicy` divergence between
Spark and Comet.
+ *
+ * Spark's `ArrayBasedMapBuilder` (used by `MapFromArrays` and
`MapFromEntries`) applies the
+ * policy on duplicate keys (`EXCEPTION` — the default, raising
`DUPLICATED_MAP_KEY` — or
+ * `LAST_WIN`, keeping the last occurrence). Comet's native `map` scalar has
no LAST_WIN path, so
+ * only the `EXCEPTION` mode agrees with Spark; `LAST_WIN` diverges and must
fall back. Duplicate-
+ * key data cases under `EXCEPTION` remain a separately tracked
user-observable divergence.
+ *
+ * Other map-building expressions (`CreateMap`, `MapConcat`, `TransformKeys`)
already delegate to
+ * Spark's own `doGenCode` via `CometCodegenDispatch`, so they inherit Spark's
dedup semantics for
+ * free and do not need this gate.
+ */
+private object MapKeyDedupPolicySupport {
+ private val LastWin = "LAST_WIN"
+
+ val incompatibleReason: String =
+ s"`${SQLConf.MAP_KEY_DEDUP_POLICY.key}` is set to `$LastWin`; Comet's
native map construction " +
+ "does not implement LAST_WIN dedup semantics."
+
+ def isLastWin: Boolean =
+ SQLConf.get.getConf(SQLConf.MAP_KEY_DEDUP_POLICY).equalsIgnoreCase(LastWin)
+}
+
object CometMapFromArrays extends CometExpressionSerde[MapFromArrays] {
+ override def getIncompatibleReasons(): Seq[String] =
+ Seq(MapKeyDedupPolicySupport.incompatibleReason)
+
+ override def getSupportLevel(expr: MapFromArrays): SupportLevel = {
+ if (MapKeyDedupPolicySupport.isLastWin) {
+ Incompatible(Some(MapKeyDedupPolicySupport.incompatibleReason))
+ } else {
+ Compatible(None)
+ }
+ }
Review Comment:
how about this:
```suggestion
private object MapKeyDedupPolicySupport {
val incompatibleReason: String =
s"`${SQLConf.MAP_KEY_DEDUP_POLICY.key}` is set to
`${SQLConf.MapKeyDedupPolicy.LAST_WIN}`; Comet's native map construction " +
"does not implement LAST_WIN dedup semantics."
def isLastWin: Boolean =
SQLConf.get.getConf(SQLConf.MAP_KEY_DEDUP_POLICY).toString.equalsIgnoreCase(
SQLConf.MapKeyDedupPolicy.LAST_WIN.toString)
```
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