Github user cloud-fan commented on a diff in the pull request: https://github.com/apache/spark/pull/20450#discussion_r165242689 --- Diff: sql/core/src/main/java/org/apache/spark/sql/vectorized/ColumnVector.java --- @@ -215,10 +215,18 @@ public final ColumnarRow getStruct(int rowId) { /** * Returns the map type value for rowId. + * + * In Spark, map type value is basically a key data array and a value data array. A key from the + * key array with a index and a value from the value array with the same index contribute to + * an entry of this map type value. + * + * To support map type, implementations must construct an {@link ColumnarMap} and return it in --- End diff -- This is very minor, may not worth to wait for another QA round. Maybe we can fix it in your "return null" PR?
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