[SPARK-1341] [Streaming] Throttle BlockGenerator to limit rate of data consumption.

Author: Issac Buenrostro <buenrostro@ooyala.com>

Closes #945 from ibuenros/SPARK-1341-throttle and squashes the following commits:

5514916 [Issac Buenrostro] Formatting changes, added documentation for streaming throttling, stricter unit tests for throttling.
62f395f [Issac Buenrostro] Add comments and license to streaming RateLimiter.scala
7066438 [Issac Buenrostro] Moved throttle code to RateLimiter class, smoother pushing when throttling active
ccafe09 [Issac Buenrostro] Throttle BlockGenerator to limit rate of data consumption.

2 files changed, 71 insertions, 1 deletions

diff --git a/streaming/src/main/scala/org/apache/spark/streaming/receiver/BlockGenerator.scala b/streaming/src/main/scala/org/apache/spark/streaming/receiver/BlockGenerator.scala
index 78cc2daa56..0316b6862f 100644
--- a/streaming/src/main/scala/org/apache/spark/streaming/receiver/BlockGenerator.scala
+++ b/streaming/src/main/scala/org/apache/spark/streaming/receiver/BlockGenerator.scala
@@ -44,7 +44,7 @@ private[streaming] class BlockGenerator(
     listener: BlockGeneratorListener,
     receiverId: Int,
     conf: SparkConf
-  ) extends Logging {
+  ) extends RateLimiter(conf) with Logging {
 
   private case class Block(id: StreamBlockId, buffer: ArrayBuffer[Any])
 
@@ -81,6 +81,7 @@ private[streaming] class BlockGenerator(
    * will be periodically pushed into BlockManager.
    */
   def += (data: Any): Unit = synchronized {
+    waitToPush()
     currentBuffer += data
   }
 
diff --git a/streaming/src/main/scala/org/apache/spark/streaming/receiver/RateLimiter.scala b/streaming/src/main/scala/org/apache/spark/streaming/receiver/RateLimiter.scala
new file mode 100644
index 0000000000..e4f6ba626e
--- /dev/null
+++ b/streaming/src/main/scala/org/apache/spark/streaming/receiver/RateLimiter.scala
@@ -0,0 +1,69 @@
+/*
+ * 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.receiver
+
+import org.apache.spark.{Logging, SparkConf}
+import java.util.concurrent.TimeUnit._
+
+/** Provides waitToPush() method to limit the rate at which receivers consume data.
+  *
+  * waitToPush method will block the thread if too many messages have been pushed too quickly,
+  * and only return when a new message has been pushed. It assumes that only one message is
+  * pushed at a time.
+  *
+  * The spark configuration spark.streaming.receiver.maxRate gives the maximum number of messages
+  * per second that each receiver will accept.
+  *
+  * @param conf spark configuration
+  */
+private[receiver] abstract class RateLimiter(conf: SparkConf) extends Logging {
+
+  private var lastSyncTime = System.nanoTime
+  private var messagesWrittenSinceSync = 0L
+  private val desiredRate = conf.getInt("spark.streaming.receiver.maxRate", 0)
+  private val SYNC_INTERVAL = NANOSECONDS.convert(10, SECONDS)
+
+  def waitToPush() {
+    if( desiredRate <= 0 ) {
+      return
+    }
+    val now = System.nanoTime
+    val elapsedNanosecs = math.max(now - lastSyncTime, 1)
+    val rate = messagesWrittenSinceSync.toDouble * 1000000000 / elapsedNanosecs
+    if (rate < desiredRate) {
+      // It's okay to write; just update some variables and return
+      messagesWrittenSinceSync += 1
+      if (now > lastSyncTime + SYNC_INTERVAL) {
+        // Sync interval has passed; let's resync
+        lastSyncTime = now
+        messagesWrittenSinceSync = 1
+      }
+    } else {
+      // Calculate how much time we should sleep to bring ourselves to the desired rate.
+      val targetTimeInMillis = messagesWrittenSinceSync * 1000 / desiredRate
+      val elapsedTimeInMillis = elapsedNanosecs / 1000000
+      val sleepTimeInMillis = targetTimeInMillis - elapsedTimeInMillis
+      if (sleepTimeInMillis > 0) {
+        logTrace("Natural rate is " + rate + " per second but desired rate is " +
+          desiredRate + ", sleeping for " + sleepTimeInMillis + " ms to compensate.")
+        Thread.sleep(sleepTimeInMillis)
+      }
+      waitToPush()
+    }
+  }
+}