[SPARK-31019][SQL] make it clear that people can deduplicate map keys

docs/sql-migration-guide.md

@@ -49,7 +49,7 @@ license: |
 
   - In Spark version 2.4 and earlier, float/double -0.0 is semantically equal to 0.0, but -0.0 and 0.0 are considered as different values when used in aggregate grouping keys, window partition keys and join keys. Since Spark 3.0, this bug is fixed. For example, `Seq(-0.0, 0.0).toDF("d").groupBy("d").count()` returns `[(0.0, 2)]` in Spark 3.0, and `[(0.0, 1), (-0.0, 1)]` in Spark 2.4 and earlier.
 
-  - In Spark version 2.4 and earlier, users can create a map with duplicated keys via built-in functions like `CreateMap`, `StringToMap`, etc. The behavior of map with duplicated keys is undefined, e.g. map look up respects the duplicated key appears first, `Dataset.collect` only keeps the duplicated key appears last, `MapKeys` returns duplicated keys, etc. Since Spark 3.0, new config `spark.sql.legacy.allowDuplicatedMapKeys` was added, with the default value `false`, Spark will throw RuntimeException while duplicated keys are found. If set to `true`, these built-in functions will remove duplicated map keys with last wins policy. Users may still read map values with duplicated keys from data sources which do not enforce it (e.g. Parquet), the behavior will be undefined.
+  - In Spark version 2.4 and earlier, users can create a map with duplicated keys via built-in functions like `CreateMap`, `StringToMap`, etc. The behavior of map with duplicated keys is undefined, e.g. map look up respects the duplicated key appears first, `Dataset.collect` only keeps the duplicated key appears last, `MapKeys` returns duplicated keys, etc. Since Spark 3.0, Spark will throw RuntimeException while duplicated keys are found. Users can set `spark.sql.mapKeyDedupPolicy` to LAST_WIN to deduplicate map keys with last wins policy. Users may still read map values with duplicated keys from data sources which do not enforce it (e.g. Parquet), the behavior will be undefined.
 
   - In Spark version 2.4 and earlier, partition column value is converted as null if it can't be casted to corresponding user provided schema. Since 3.0, partition column value is validated with user provided schema. An exception is thrown if the validation fails. You can disable such validation by setting `spark.sql.sources.validatePartitionColumns` to `false`.
 

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/ArrayBasedMapBuilder.scala

@@ -21,7 +21,6 @@ import scala.collection.mutable
 
 import org.apache.spark.sql.catalyst.InternalRow
 import org.apache.spark.sql.internal.SQLConf
-import org.apache.spark.sql.internal.SQLConf.LEGACY_ALLOW_DUPLICATED_MAP_KEY
 import org.apache.spark.sql.types._
 import org.apache.spark.unsafe.array.ByteArrayMethods
 
@@ -49,8 +48,7 @@ class ArrayBasedMapBuilder(keyType: DataType, valueType: DataType) extends Seria
   private lazy val keyGetter = InternalRow.getAccessor(keyType)
   private lazy val valueGetter = InternalRow.getAccessor(valueType)
 
-  private val allowDuplicatedMapKey =
-    SQLConf.get.getConf(LEGACY_ALLOW_DUPLICATED_MAP_KEY)
+  private val mapKeyDedupPolicy = SQLConf.get.getConf(SQLConf.MAP_KEY_DEDUP_POLICY)
 
   def put(key: Any, value: Any): Unit = {
     if (key == null) {
@@ -67,13 +65,17 @@ class ArrayBasedMapBuilder(keyType: DataType, valueType: DataType) extends Seria
       keys.append(key)
       values.append(value)
     } else {
-      if (!allowDuplicatedMapKey) {
-        throw new RuntimeException(s"Duplicate map key $key was founded, please check the input " +
-          "data. If you want to remove the duplicated keys with last-win policy, you can set " +
-          s"${LEGACY_ALLOW_DUPLICATED_MAP_KEY.key} to true.")
+      if (mapKeyDedupPolicy == SQLConf.MapKeyDedupPolicy.EXCEPTION.toString) {
+        throw new RuntimeException(s"Duplicate map key $key was found, please check the input " +
+          "data. If you want to remove the duplicated keys, you can set " +
+          s"${SQLConf.MAP_KEY_DEDUP_POLICY.key} to ${SQLConf.MapKeyDedupPolicy.LAST_WIN} so that " +
+          "the key inserted at last takes precedence.")
+      } else if (mapKeyDedupPolicy == SQLConf.MapKeyDedupPolicy.LAST_WIN.toString) {
+        // Overwrite the previous value, as the policy is last wins.
+        values(index) = value
+      } else {
+        throw new IllegalStateException("Unknown map key dedup policy: " + mapKeyDedupPolicy)
       }
-      // Overwrite the previous value, as the policy is last wins.
-      values(index) = value
     }
   }
 

sql/catalyst/src/main/scala/org/apache/spark/sql/internal/SQLConf.scala

@@ -2329,6 +2329,21 @@ object SQLConf {
       .stringConf
       .createOptional
 
+  object MapKeyDedupPolicy extends Enumeration {
+    val EXCEPTION, LAST_WIN = Value
+  }
+
+  val MAP_KEY_DEDUP_POLICY = buildConf("spark.sql.mapKeyDedupPolicy")
+    .doc("The policy to deduplicate map keys in builtin function: CreateMap, MapFromArrays, " +
+      "MapFromEntries, StringToMap, MapConcat and TransformKeys. When EXCEPTION, the query " +
+      "fails if duplicated map keys are detected. When LAST_WIN, the map key that is inserted " +
+      "at last takes precedence.")
+    .version("3.0.0")
+    .stringConf
+    .transform(_.toUpperCase(Locale.ROOT))
+    .checkValues(MapKeyDedupPolicy.values.map(_.toString))
+    .createWithDefault(MapKeyDedupPolicy.EXCEPTION.toString)
+
   val LEGACY_LOOSE_UPCAST = buildConf("spark.sql.legacy.doLooseUpcast")
     .internal()
     .doc("When true, the upcast will be loose and allows string to atomic types.")
@@ -2435,17 +2450,6 @@ object SQLConf {
     .booleanConf
     .createWithDefault(false)
 
-  val LEGACY_ALLOW_DUPLICATED_MAP_KEY =
-    buildConf("spark.sql.legacy.allowDuplicatedMapKeys")
-      .doc("When true, use last wins policy to remove duplicated map keys in built-in functions, " +
-        "this config takes effect in below build-in functions: CreateMap, MapFromArrays, " +
-        "MapFromEntries, StringToMap, MapConcat and TransformKeys. Otherwise, if this is false, " +
-        "which is the default, Spark will throw an exception when duplicated map keys are " +
-        "detected.")
-      .version("")
-      .booleanConf
-      .createWithDefault(false)
-
   val LEGACY_ALLOW_HASH_ON_MAPTYPE = buildConf("spark.sql.legacy.allowHashOnMapType")
     .doc("When set to true, hash expressions can be applied on elements of MapType. Otherwise, " +
       "an analysis exception will be thrown.")

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/CollectionExpressionsSuite.scala

@@ -139,7 +139,9 @@ class CollectionExpressionsSuite extends SparkFunSuite with ExpressionEvalHelper
       MapType(IntegerType, IntegerType, valueContainsNull = true))
     val mNull = Literal.create(null, MapType(StringType, StringType))
 
-    withSQLConf(SQLConf.LEGACY_ALLOW_DUPLICATED_MAP_KEY.key -> "true") {
+    checkExceptionInExpression[RuntimeException](
+      MapConcat(Seq(m0, m1)), "Duplicate map key")
+    withSQLConf(SQLConf.MAP_KEY_DEDUP_POLICY.key -> SQLConf.MapKeyDedupPolicy.LAST_WIN.toString) {
       // overlapping maps should remove duplicated map keys w.r.t. last win policy.
       checkEvaluation(MapConcat(Seq(m0, m1)), create_map("a" -> "4", "b" -> "2", "c" -> "3"))
     }
@@ -274,7 +276,10 @@ class CollectionExpressionsSuite extends SparkFunSuite with ExpressionEvalHelper
     checkEvaluation(MapFromEntries(ai1), create_map(1 -> null, 2 -> 20, 3 -> null))
     checkEvaluation(MapFromEntries(ai2), Map.empty)
     checkEvaluation(MapFromEntries(ai3), null)
-    withSQLConf(SQLConf.LEGACY_ALLOW_DUPLICATED_MAP_KEY.key -> "true") {
+
+    checkExceptionInExpression[RuntimeException](
+      MapFromEntries(ai4), "Duplicate map key")
+    withSQLConf(SQLConf.MAP_KEY_DEDUP_POLICY.key -> SQLConf.MapKeyDedupPolicy.LAST_WIN.toString) {
       // Duplicated map keys will be removed w.r.t. the last wins policy.
       checkEvaluation(MapFromEntries(ai4), create_map(1 -> 20))
     }
@@ -298,7 +303,10 @@ class CollectionExpressionsSuite extends SparkFunSuite with ExpressionEvalHelper
     checkEvaluation(MapFromEntries(as1), create_map("a" -> null, "b" -> "bb", "c" -> null))
     checkEvaluation(MapFromEntries(as2), Map.empty)
     checkEvaluation(MapFromEntries(as3), null)
-    withSQLConf(SQLConf.LEGACY_ALLOW_DUPLICATED_MAP_KEY.key -> "true") {
+
+    checkExceptionInExpression[RuntimeException](
+      MapFromEntries(as4), "Duplicate map key")
+    withSQLConf(SQLConf.MAP_KEY_DEDUP_POLICY.key -> SQLConf.MapKeyDedupPolicy.LAST_WIN.toString) {
       // Duplicated map keys will be removed w.r.t. the last wins policy.
       checkEvaluation(MapFromEntries(as4), create_map("a" -> "bb"))
     }

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/ComplexTypeSuite.scala

@@ -217,7 +217,9 @@ class ComplexTypeSuite extends SparkFunSuite with ExpressionEvalHelper {
       CreateMap(interlace(strWithNull, intSeq.map(Literal(_)))),
       "Cannot use null as map key")
 
-    withSQLConf(SQLConf.LEGACY_ALLOW_DUPLICATED_MAP_KEY.key -> "true") {
+    checkExceptionInExpression[RuntimeException](
+      CreateMap(Seq(Literal(1), Literal(2), Literal(1), Literal(3))), "Duplicate map key")
+    withSQLConf(SQLConf.MAP_KEY_DEDUP_POLICY.key -> SQLConf.MapKeyDedupPolicy.LAST_WIN.toString) {
       // Duplicated map keys will be removed w.r.t. the last wins policy.
       checkEvaluation(
         CreateMap(Seq(Literal(1), Literal(2), Literal(1), Literal(3))),
@@ -284,7 +286,12 @@ class ComplexTypeSuite extends SparkFunSuite with ExpressionEvalHelper {
       MapFromArrays(intWithNullArray, strArray),
       "Cannot use null as map key")
 
-    withSQLConf(SQLConf.LEGACY_ALLOW_DUPLICATED_MAP_KEY.key -> "true") {
+    checkExceptionInExpression[RuntimeException](
+      MapFromArrays(
+        Literal.create(Seq(1, 1), ArrayType(IntegerType)),
+        Literal.create(Seq(2, 3), ArrayType(IntegerType))),
+      "Duplicate map key")
+    withSQLConf(SQLConf.MAP_KEY_DEDUP_POLICY.key -> SQLConf.MapKeyDedupPolicy.LAST_WIN.toString) {
       // Duplicated map keys will be removed w.r.t. the last wins policy.
       checkEvaluation(
         MapFromArrays(
@@ -404,7 +411,9 @@ class ComplexTypeSuite extends SparkFunSuite with ExpressionEvalHelper {
     val m5 = Map("a" -> null)
     checkEvaluation(new StringToMap(s5), m5)
 
-    withSQLConf(SQLConf.LEGACY_ALLOW_DUPLICATED_MAP_KEY.key -> "true") {
+    checkExceptionInExpression[RuntimeException](
+      new StringToMap(Literal("a:1,b:2,a:3")), "Duplicate map key")
+    withSQLConf(SQLConf.MAP_KEY_DEDUP_POLICY.key -> SQLConf.MapKeyDedupPolicy.LAST_WIN.toString) {
       // Duplicated map keys will be removed w.r.t. the last wins policy.
       checkEvaluation(
         new StringToMap(Literal("a:1,b:2,a:3")),

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/HigherOrderFunctionsSuite.scala

@@ -465,7 +465,10 @@ class HigherOrderFunctionsSuite extends SparkFunSuite with ExpressionEvalHelper
     checkEvaluation(
       transformKeys(transformKeys(ai0, plusOne), plusValue),
       create_map(3 -> 1, 5 -> 2, 7 -> 3, 9 -> 4))
-    withSQLConf(SQLConf.LEGACY_ALLOW_DUPLICATED_MAP_KEY.key -> "true") {
+
+    checkExceptionInExpression[RuntimeException](
+      transformKeys(ai0, modKey), "Duplicate map key")
+    withSQLConf(SQLConf.MAP_KEY_DEDUP_POLICY.key -> SQLConf.MapKeyDedupPolicy.LAST_WIN.toString) {
       // Duplicated map keys will be removed w.r.t. the last wins policy.
       checkEvaluation(transformKeys(ai0, modKey), create_map(1 -> 4, 2 -> 2, 0 -> 3))
     }

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/util/ArrayBasedMapBuilderSuite.scala

@@ -48,11 +48,11 @@ class ArrayBasedMapBuilderSuite extends SparkFunSuite with SQLHelper {
     val builder = new ArrayBasedMapBuilder(IntegerType, IntegerType)
     builder.put(1, 1)
     val e = intercept[RuntimeException](builder.put(1, 2))
-    assert(e.getMessage.contains("Duplicate map key 1 was founded"))
+    assert(e.getMessage.contains("Duplicate map key 1 was found"))
   }
 
   test("remove duplicated keys with last wins policy") {
-    withSQLConf(SQLConf.LEGACY_ALLOW_DUPLICATED_MAP_KEY.key -> "true") {
+    withSQLConf(SQLConf.MAP_KEY_DEDUP_POLICY.key -> SQLConf.MapKeyDedupPolicy.LAST_WIN.toString) {
       val builder = new ArrayBasedMapBuilder(IntegerType, IntegerType)
       builder.put(1, 1)
       builder.put(2, 2)
@@ -63,8 +63,15 @@ class ArrayBasedMapBuilderSuite extends SparkFunSuite with SQLHelper {
     }
   }
 
-  test("binary type key") {
-    withSQLConf(SQLConf.LEGACY_ALLOW_DUPLICATED_MAP_KEY.key -> "true") {
+  test("binary type key with duplication") {
+    val builder = new ArrayBasedMapBuilder(BinaryType, IntegerType)
+    builder.put(Array(1.toByte), 1)
+    builder.put(Array(2.toByte), 2)
+    val e = intercept[RuntimeException](builder.put(Array(1.toByte), 3))
+    // By default duplicated map key fails the query.
+    assert(e.getMessage.contains("Duplicate map key"))
+
+    withSQLConf(SQLConf.MAP_KEY_DEDUP_POLICY.key -> SQLConf.MapKeyDedupPolicy.LAST_WIN.toString) {
       val builder = new ArrayBasedMapBuilder(BinaryType, IntegerType)
       builder.put(Array(1.toByte), 1)
       builder.put(Array(2.toByte), 2)
@@ -79,39 +86,55 @@ class ArrayBasedMapBuilderSuite extends SparkFunSuite with SQLHelper {
     }
   }
 
-  test("struct type key") {
-    withSQLConf(SQLConf.LEGACY_ALLOW_DUPLICATED_MAP_KEY.key -> "true") {
+  test("struct type key with duplication") {
+    val unsafeRow = {
+      val row = new UnsafeRow(1)
+      val bytes = new Array[Byte](16)
+      row.pointTo(bytes, 16)
+      row.setInt(0, 1)
+      row
+    }
+
+    val builder = new ArrayBasedMapBuilder(new StructType().add("i", "int"), IntegerType)
+    builder.put(InternalRow(1), 1)
+    builder.put(InternalRow(2), 2)
+    val e = intercept[RuntimeException](builder.put(unsafeRow, 3))
+    // By default duplicated map key fails the query.
+    assert(e.getMessage.contains("Duplicate map key"))
+
+    withSQLConf(SQLConf.MAP_KEY_DEDUP_POLICY.key -> SQLConf.MapKeyDedupPolicy.LAST_WIN.toString) {
       val builder = new ArrayBasedMapBuilder(new StructType().add("i", "int"), IntegerType)
       builder.put(InternalRow(1), 1)
       builder.put(InternalRow(2), 2)
-      val unsafeRow = {
-        val row = new UnsafeRow(1)
-        val bytes = new Array[Byte](16)
-        row.pointTo(bytes, 16)
-        row.setInt(0, 1)
-        row
-      }
       builder.put(unsafeRow, 3)
       val map = builder.build()
       assert(map.numElements() == 2)
       assert(ArrayBasedMapData.toScalaMap(map) == Map(InternalRow(1) -> 3, InternalRow(2) -> 2))
     }
   }
 
-  test("array type key") {
-    withSQLConf(SQLConf.LEGACY_ALLOW_DUPLICATED_MAP_KEY.key -> "true") {
+  test("array type key with duplication") {
+    val unsafeArray = {
+      val array = new UnsafeArrayData()
+      val bytes = new Array[Byte](24)
+      Platform.putLong(bytes, Platform.BYTE_ARRAY_OFFSET, 2)
+      array.pointTo(bytes, Platform.BYTE_ARRAY_OFFSET, 24)
+      array.setInt(0, 1)
+      array.setInt(1, 1)
+      array
+    }
+
+    val builder = new ArrayBasedMapBuilder(ArrayType(IntegerType), IntegerType)
+    builder.put(new GenericArrayData(Seq(1, 1)), 1)
+    builder.put(new GenericArrayData(Seq(2, 2)), 2)
+    val e = intercept[RuntimeException](builder.put(unsafeArray, 3))
+    // By default duplicated map key fails the query.
+    assert(e.getMessage.contains("Duplicate map key"))
+
+    withSQLConf(SQLConf.MAP_KEY_DEDUP_POLICY.key -> SQLConf.MapKeyDedupPolicy.LAST_WIN.toString) {
       val builder = new ArrayBasedMapBuilder(ArrayType(IntegerType), IntegerType)
       builder.put(new GenericArrayData(Seq(1, 1)), 1)
       builder.put(new GenericArrayData(Seq(2, 2)), 2)
-      val unsafeArray = {
-        val array = new UnsafeArrayData()
-        val bytes = new Array[Byte](24)
-        Platform.putLong(bytes, Platform.BYTE_ARRAY_OFFSET, 2)
-        array.pointTo(bytes, Platform.BYTE_ARRAY_OFFSET, 24)
-        array.setInt(0, 1)
-        array.setInt(1, 1)
-        array
-      }
       builder.put(unsafeArray, 3)
       val map = builder.build()
       assert(map.numElements() == 2)

sql/core/src/test/scala/org/apache/spark/sql/DataFrameFunctionsSuite.scala

@@ -23,6 +23,7 @@ import java.util.TimeZone
 
 import scala.util.Random
 
+import org.apache.spark.SparkException
 import org.apache.spark.sql.catalyst.InternalRow
 import org.apache.spark.sql.catalyst.expressions.Expression
 import org.apache.spark.sql.catalyst.expressions.codegen.CodegenFallback
@@ -651,7 +652,9 @@ class DataFrameFunctionsSuite extends QueryTest with SharedSparkSession {
       Row(null)
     )
 
-    withSQLConf(SQLConf.LEGACY_ALLOW_DUPLICATED_MAP_KEY.key -> "true") {
+    intercept[SparkException](df1.selectExpr("map_concat(map1, map2)").collect())
+    intercept[SparkException](df1.select(map_concat($"map1", $"map2")).collect())
+    withSQLConf(SQLConf.MAP_KEY_DEDUP_POLICY.key -> SQLConf.MapKeyDedupPolicy.LAST_WIN.toString) {
       checkAnswer(df1.selectExpr("map_concat(map1, map2)"), expected1a)
       checkAnswer(df1.select(map_concat($"map1", $"map2")), expected1a)
     }
@@ -3070,7 +3073,13 @@ class DataFrameFunctionsSuite extends QueryTest with SharedSparkSession {
       checkAnswer(dfExample2.select(transform_keys(col("j"), (k, v) => k + v)),
         Seq(Row(Map(2.0 -> 1.0, 3.4 -> 1.4, 4.7 -> 1.7))))
 
-      withSQLConf(SQLConf.LEGACY_ALLOW_DUPLICATED_MAP_KEY.key -> "true") {
+      intercept[SparkException] {
+        dfExample3.selectExpr("transform_keys(x, (k, v) ->  k % 2 = 0 OR v)").collect()
+      }
+      intercept[SparkException] {
+        dfExample3.select(transform_keys(col("x"), (k, v) => k % 2 === 0 || v)).collect()
+      }
+      withSQLConf(SQLConf.MAP_KEY_DEDUP_POLICY.key -> SQLConf.MapKeyDedupPolicy.LAST_WIN.toString) {
         checkAnswer(dfExample3.selectExpr("transform_keys(x, (k, v) ->  k % 2 = 0 OR v)"),
           Seq(Row(Map(true -> true, true -> false))))