Why does a single structured query run multiple SQL queries per batch?

问题

Why does the following structured query run multiple SQL queries as can be seen in web UI's SQL tab?

import org.apache.spark.sql.streaming.{OutputMode, Trigger}
import scala.concurrent.duration._
val rates = spark.
  readStream.
  format("rate").
  option("numPartitions", 1).
  load.
  writeStream.
  format("console").
  option("truncate", false).
  option("numRows", 10).
  trigger(Trigger.ProcessingTime(10.seconds)).
  queryName("rate-console").
  start

来源：https://stackoverflow.com/questions/46162143/why-does-a-single-structured-query-run-multiple-sql-queries-per-batch