Github user dragos commented on a diff in the pull request:
https://github.com/apache/spark/pull/7648#discussion_r35956641
--- Diff:
streaming/src/main/scala/org/apache/spark/streaming/scheduler/rate/PIDRateEstimator.scala
---
@@ -0,0 +1,109 @@
+/*
+ * 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. 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.
--- End diff --
I don't think we should limit the range to [0, 1]. There is no such limit
in a typical PID controller, and I'm not sure we stand much to gain. These are
just constants. We could require them to be strictly positive and modify the
formula, but we're departing from PID theory. Presumably that makes sense in
our domain.
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