Github user tdas commented on a diff in the pull request:
https://github.com/apache/spark/pull/7648#discussion_r35960575
--- Diff:
streaming/src/main/scala/org/apache/spark/streaming/scheduler/rate/PIDRateEstimator.scala
---
@@ -0,0 +1,124 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.streaming.scheduler.rate
+
+/**
+ * Implements a proportional-integral-derivative (PID) controller which
acts on
+ * the speed of ingestion of elements into Spark Streaming. A PID
controller works
+ * by calculating an '''error''' between a measured output and a desired
value. In the
+ * case of Spark Streaming the error is the difference between the
measured processing
+ * rate (number of elements/processing delay) and the previous rate.
+ *
+ * @see https://en.wikipedia.org/wiki/PID_controller
+ *
+ * @param batchDurationMillis the batch duration, in milliseconds
+ * @param proportional how much the correction should depend on the current
+ * error. This term usually provides the bulk of correction and
should be positive or zero.
+ * A value too large would make the controller overshoot the
setpoint, while a small value
+ * would make the controller too insensitive. The default value is
1.
+ * @param integral how much the correction should depend on the
accumulation
+ * of past errors. This value should be positive or 0. This term
accelerates the movement
+ * towards the desired value, but a large value may lead to
overshooting. The default value
+ * is 0.2.
+ * @param derivative how much the correction should depend on a prediction
+ * of future errors, based on current rate of change. This value
should be positive or 0.
+ * This term is not used very often, as it impacts stability of the
system. The default
+ * value is 0.
+ */
+private[streaming] class PIDRateEstimator(
+ batchIntervalMillis: Long,
+ proportional: Double = 1D,
--- End diff --
nit: I dont particularly mind, but is there any particular reason for
having D at the end everywhere. Looks pretty weird.
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