Second approach

import java.sql._
dataframe.coalesce("NUMBER OF WORKERS").mapPartitions((d) => Iterator(d)).foreach { batch =>
val dbc: Connection = DriverManager.getConnection("JDBCURL")
val st: PreparedStatement = dbc.prepareStatement("YOUR PREPARED STATEMENT")

batch.grouped("# Of Rows you want per batch").foreach { session =>
  session.foreach { x =>
    st.setDouble(1, x.getDouble(1)) 
    st.addBatch()
  }
  st.executeBatch()
}
dbc.close()
  }
This will execute batches for each worker and close the DB connection. It gives you control over how many workers, how many batches and allows you to work within those confines.

Spark postgresql jdbc output

import java.io.InputStream

import org.apache.spark.sql.execution.datasources.jdbc.JdbcUtils
import org.apache.spark.sql.{ DataFrame, Row }

import org.postgresql.copy.CopyManager
import org.postgresql.core.BaseConnection

val jdbcUrl = s"jdbc:postgresql://..." // db credentials elided
val connectionProperties = {
  val props = new java.util.Properties()

  props.setProperty("driver", "org.postgresql.Driver")

  props
}

// Spark reads the "driver" property to allow users to override the default driver selected, otherwise
// it picks the Redshift driver, which doesn't support JDBC CopyManager.
// https://github.com/apache/spark/blob/v1.6.1/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/jdbc/JdbcUtils.scala#L44-51
val cf: () => Connection = JdbcUtils.createConnectionFactory(jdbcUrl, connectionProperties)

// Convert every partition (an `Iterator[Row]`) to bytes (InputStream)
def rowsToInputStream(rows: Iterator[Row], delimiter: String): InputStream = {
  val bytes: Iterator[Byte] = rows.map { row =>
    (row.mkString(delimiter) + "\n").getBytes
  }.flatten

  override def read(): Int = if (bytes.hasNext) {
    bytes.next & 0xff // bitwise AND - make the signed byte an unsigned int from 0-255
  } else {
    -1
  }
}

// Beware: this will open a db connection for every partition of your DataFrame.
frame.foreachPartition { rows =>
  val conn = cf()
  val cm = new CopyManager(conn.asInstanceOf[BaseConnection])

  cm.copyIn(
    """COPY my_schema._mytable FROM STDIN WITH (NULL 'null', FORMAT CSV, DELIMITER E'\t')""", // adjust COPY settings as you desire, options from https://www.postgresql.org/docs/9.5/static/sql-copy.html
    rowsToInputStream(rows, "\t"))

  conn.close()
}