我正在测试 Spark 2.4.0 新的 from_avro 和 to_avro 函数。
我创建了一个只有一列和三行的数据框，用 avro 对其进行序列化，然后从 avro 将其反序列化。
如果输入数据集创建为
val input1 = Seq("foo", "bar", "baz").toDF("key")
+---+
|key|
+---+
|foo|
|bar|
|baz|
+---+
反序列化只返回最后一行的 N 个副本：
+---+
|key|
+---+
|baz|
|baz|
|baz|
+---+
如果我将输入数据集创建为
val input2 = input1.sqlContext.createDataFrame(input1.rdd, input1.schema)
结果是正确的：
+---+
|key|
+---+
|foo|
|bar|
|baz|
+---+
示例代码：
import org.apache.spark.sql.avro.{SchemaConverters, from_avro, to_avro}
import org.apache.spark.sql.DataFrame
val input1 = Seq("foo", "bar", "baz").toDF("key")
val input2 = input1.sqlContext.createDataFrame(input1.rdd, input1.schema)
def test_avro(df: DataFrame): Unit = {
println("input df:")
df.printSchema()
df.show()
val keySchema = SchemaConverters.toAvroType(df.schema).toString
println(s"avro schema: $keySchema")
val avroDf = df
.select(to_avro($"key") as "key")
println("avro serialized:")
avroDf.printSchema()
avroDf.show()
val output = avroDf
.select(from_avro($"key", keySchema) as "key")
.select("key.*")
println("avro deserialized:")
output.printSchema()
output.show()
}
println("############### testing .toDF()")
test_avro(input1)
println("############### testing .createDataFrame()")
test_avro(input2)
结果：
############### testing .toDF()
input df:
root
|-- key: string (nullable = true)
+---+
|key|
+---+
|foo|
|bar|
|baz|
+---+
avro schema: {"type":"record","name":"topLevelRecord","fields":[{"name":"key","type":["string","null"]}]}
avro serialized:
root
|-- key: binary (nullable = true)
+----------------+
| key|
+----------------+
|[00 06 66 6F 6F]|
|[00 06 62 61 72]|
|[00 06 62 61 7A]|
+----------------+
avro deserialized:
root
|-- key: string (nullable = true)
+---+
|key|
+---+
|baz|
|baz|
|baz|
+---+
############### testing .createDataFrame()
input df:
root
|-- key: string (nullable = true)
+---+
|key|
+---+
|foo|
|bar|
|baz|
+---+
avro schema: {"type":"record","name":"topLevelRecord","fields":[{"name":"key","type":["string","null"]}]}
avro serialized:
root
|-- key: binary (nullable = true)
+----------------+
| key|
+----------------+
|[00 06 66 6F 6F]|
|[00 06 62 61 72]|
|[00 06 62 61 7A]|
+----------------+
avro deserialized:
root
|-- key: string (nullable = true)
+---+
|key|
+---+
|foo|
|bar|
|baz|
+---+
从测试看来，问题出在反序列化阶段，因为打印 avro 序列化的 df 显示不同的行。
我做错了还是有错误？