title: Write spark dataframe to postgres Database
body: <p>The spark cluster setting is as follows:</p>
  
  <pre><code>conf['SparkConfiguration'] = SparkConf() \
  .setMaster('yarn-client') \
  .setAppName("test") \
  .set("spark.executor.memory", "20g") \
  .set("spark.driver.maxResultSize", "20g") \
  .set("spark.executor.instances", "20")\
  .set("spark.executor.cores", "3") \
  .set("spark.memory.fraction", "0.2") \
  .set("user", "test_user") \
  .set("spark.executor.extraClassPath", "/usr/share/java/postgresql-jdbc3.jar")
  </code></pre>
  
  <p>When I try to write the dataframe to the Postgres DB using the following code: </p>
  
  <pre><code>from pyspark.sql import DataFrameWriter
  my_writer = DataFrameWriter(df)
  
  url_connect = "jdbc:postgresql://198.123.43.24:1234"
  table = "test_result"
  mode = "overwrite"
  properties = {"user":"postgres", "password":"password"}
  
  my_writer.jdbc(url_connect, table, mode, properties)
  </code></pre>
  
  <p>I encounter the below error: </p>
  
  <pre><code>Py4JJavaError: An error occurred while calling o1120.jdbc.   
  :java.sql.SQLException: No suitable driver
      at java.sql.DriverManager.getDriver(DriverManager.java:278)
  at org.apache.spark.sql.execution.datasources.jdbc.JdbcUtils$$anonfun$2.apply(JdbcUtils.scala:50)
  at org.apache.spark.sql.execution.datasources.jdbc.JdbcUtils$$anonfun$2.apply(JdbcUtils.scala:50)
  at scala.Option.getOrElse(Option.scala:120)
  at org.apache.spark.sql.execution.datasources.jdbc.JdbcUtils$.createConnectionFactory(JdbcUtils.scala:49)
  at org.apache.spark.sql.DataFrameWriter.jdbc(DataFrameWriter.scala:278)
  at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
  at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  at java.lang.reflect.Method.invoke(Method.java:606)
  at py4j.reflection.MethodInvoker.invoke(MethodInvoker.java:231)
  at py4j.reflection.ReflectionEngine.invoke(ReflectionEngine.java:381)
  at py4j.Gateway.invoke(Gateway.java:259)
  at py4j.commands.AbstractCommand.invokeMethod(AbstractCommand.java:133)
  at py4j.commands.CallCommand.execute(CallCommand.java:79)
  at py4j.GatewayConnection.run(GatewayConnection.java:209)
  at java.lang.Thread.run(Thread.java:745)
  </code></pre>
  
  <p>Can anyone provide some suggestions on this?
  Thank you!</p>