我究竟做错了什么？尝试使用 PySpark 连接到 mySql 数据库，但我不断收到加载错误

Question

我正在尝试使用 PySpark 连接到 mySql 数据库，但收到错误消息。我不知道下面 SparkSession 代码中的配置设置意味着什么——这是我第一次尝试使用 spark，所以我一直在关注https://towardsdatascience.com/create-your-first-etl-pipeline-in-apache-spark-and-python-ec3d12e2c169 之类的教程。

我尝试连接的 mySql 数据库可通过 Sequel Pro 访问，并且我已使用我在此处输入代码的凭据成功连接到它（mytable 不是文字表，同样 mydb 和 mypass 是不同的字符串)。

scSpark = SparkSession \
        .builder \
        .appName("reading csv") \
        .config("spark.driver.extraClassPath", "/usr/local/spark/jars/mysql-connector-java-8.0.16.jar") \
        .getOrCreate()

from pyspark.sql import SQLContext
mySqlContext = SQLContext(scSpark)

然后我运行下面的代码并收到错误...

    url="jdbc:mysql://localhost:3306/mydb",
    driver = "com.mysql.jdbc.Driver",
    dbtable = "mytable",
    user="guest",
    password="mypass").load()

这是错误：

<ipython-input-27-811547d9be98> in <module>()
      4     dbtable = "mytable",
      5     user="guest",
----> 6     password="mypass").load()

/anaconda3/lib/python3.6/site-packages/pyspark/sql/readwriter.py in load(self, path, format, schema, **options)
    170             return self._df(self._jreader.load(self._spark._sc._jvm.PythonUtils.toSeq(path)))
    171         else:
--> 172             return self._df(self._jreader.load())
    173 
    174     @since(1.4)

/anaconda3/lib/python3.6/site-packages/py4j/java_gateway.py in __call__(self, *args)
   1255         answer = self.gateway_client.send_command(command)
   1256         return_value = get_return_value(
-> 1257             answer, self.gateway_client, self.target_id, self.name)
   1258 
   1259         for temp_arg in temp_args:

/anaconda3/lib/python3.6/site-packages/pyspark/sql/utils.py in deco(*a, **kw)
     61     def deco(*a, **kw):
     62         try:
---> 63             return f(*a, **kw)
     64         except py4j.protocol.Py4JJavaError as e:
     65             s = e.java_exception.toString()

/anaconda3/lib/python3.6/site-packages/py4j/protocol.py in get_return_value(answer, gateway_client, target_id, name)
    326                 raise Py4JJavaError(
    327                     "An error occurred while calling {0}{1}{2}.\n".
--> 328                     format(target_id, ".", name), value)
    329             else:
    330                 raise Py4JError(

Py4JJavaError: An error occurred while calling o340.load.
: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
    at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
    at org.apache.spark.sql.execution.datasources.jdbc.DriverRegistry$.register(DriverRegistry.scala:45)
    at org.apache.spark.sql.execution.datasources.jdbc.JDBCOptions$$anonfun$5.apply(JDBCOptions.scala:99)
    at org.apache.spark.sql.execution.datasources.jdbc.JDBCOptions$$anonfun$5.apply(JDBCOptions.scala:99)
    at scala.Option.foreach(Option.scala:257)
    at org.apache.spark.sql.execution.datasources.jdbc.JDBCOptions.<init>(JDBCOptions.scala:99)
    at org.apache.spark.sql.execution.datasources.jdbc.JDBCOptions.<init>(JDBCOptions.scala:35)
    at org.apache.spark.sql.execution.datasources.jdbc.JdbcRelationProvider.createRelation(JdbcRelationProvider.scala:32)
    at org.apache.spark.sql.execution.datasources.DataSource.resolveRelation(DataSource.scala:318)
    at org.apache.spark.sql.DataFrameReader.loadV1Source(DataFrameReader.scala:223)
    at org.apache.spark.sql.DataFrameReader.load(DataFrameReader.scala:211)
    at org.apache.spark.sql.DataFrameReader.load(DataFrameReader.scala:167)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at py4j.reflection.MethodInvoker.invoke(MethodInvoker.java:244)
    at py4j.reflection.ReflectionEngine.invoke(ReflectionEngine.java:357)
    at py4j.Gateway.invoke(Gateway.java:282)
    at py4j.commands.AbstractCommand.invokeMethod(AbstractCommand.java:132)
    at py4j.commands.CallCommand.execute(CallCommand.java:79)
    at py4j.GatewayConnection.run(GatewayConnection.java:238)
    at java.lang.Thread.run(Thread.java:748)

Answer 1

你可以使用这个辅助函数。如果驱动程序不存在，它将下载驱动程序：

def connect_to_sql(
        spark, jdbc_hostname, jdbc_port, database, data_table, username, password
):
    jdbc_url = "jdbc:mysql://{0}:{1}/{2}".format(jdbc_hostname, jdbc_port, database)

    connection_details = {
        "user": username,
        "password": password,
        "driver": "com.mysql.cj.jdbc.Driver",
    }

    df = spark.read.jdbc(url=jdbc_url, table=data_table, properties=connection_details)
    return df

spark 是一个SparkSession 对象。