[Spark-5708] Add Slf4jSink to Spark Metrics

Add Slf4jSink to Spark Metrics using Coda Hale's SlfjReporter.
This sends metrics to log4j, allowing spark users to reuse log4j pipeline for metrics collection.

Reviewed existing unit tests and didn't see any sink-related tests. Please advise on if tests should be added.

Author: Judy <judynash@microsoft.com>
Author: judynash <judynash@microsoft.com>

Closes apache#4644 from judynash/master and squashes the following commits:

57ef214 [judynash] doc clarification and indent fixes
a751a66 [Judy] Spark-5708: Add Slf4jSink to Spark Metrics

conf/metrics.properties.template

@@ -122,6 +122,15 @@
 
 #worker.sink.csv.unit=minutes
 
+# Enable Slf4jSink for all instances by class name
+#*.sink.slf4j.class=org.apache.spark.metrics.sink.Slf4jSink
+
+# Polling period for Slf4JSink
+#*.sink.sl4j.period=1
+
+#*.sink.sl4j.unit=minutes
+
+
 # Enable jvm source for instance master, worker, driver and executor
 #master.source.jvm.class=org.apache.spark.metrics.source.JvmSource
 

core/src/main/scala/org/apache/spark/metrics/sink/Slf4jSink.scala

@@ -0,0 +1,68 @@
+/*
+ * 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.metrics.sink
+
+import java.util.Properties
+import java.util.concurrent.TimeUnit
+
+import com.codahale.metrics.{Slf4jReporter, MetricRegistry}
+
+import org.apache.spark.SecurityManager
+import org.apache.spark.metrics.MetricsSystem
+
+private[spark] class Slf4jSink(
+    val property: Properties, 
+    val registry: MetricRegistry,
+    securityMgr: SecurityManager) 
+  extends Sink {
+  val SLF4J_DEFAULT_PERIOD = 10
+  val SLF4J_DEFAULT_UNIT = "SECONDS"
+
+  val SLF4J_KEY_PERIOD = "period"
+  val SLF4J_KEY_UNIT = "unit"
+
+  val pollPeriod = Option(property.getProperty(SLF4J_KEY_PERIOD)) match {
+    case Some(s) => s.toInt
+    case None => SLF4J_DEFAULT_PERIOD
+  }
+
+  val pollUnit: TimeUnit = Option(property.getProperty(SLF4J_KEY_UNIT)) match {
+    case Some(s) => TimeUnit.valueOf(s.toUpperCase())
+    case None => TimeUnit.valueOf(SLF4J_DEFAULT_UNIT)
+  }
+
+  MetricsSystem.checkMinimalPollingPeriod(pollUnit, pollPeriod)
+
+  val reporter: Slf4jReporter = Slf4jReporter.forRegistry(registry)
+    .convertDurationsTo(TimeUnit.MILLISECONDS)
+    .convertRatesTo(TimeUnit.SECONDS)
+    .build()
+
+  override def start() {
+    reporter.start(pollPeriod, pollUnit)
+  }
+
+  override def stop() {
+    reporter.stop()
+  }
+
+  override def report() {
+    reporter.report()
+  }
+}
+

docs/monitoring.md

@@ -176,6 +176,7 @@ Each instance can report to zero or more _sinks_. Sinks are contained in the
 * `JmxSink`: Registers metrics for viewing in a JMX console.
 * `MetricsServlet`: Adds a servlet within the existing Spark UI to serve metrics data as JSON data.
 * `GraphiteSink`: Sends metrics to a Graphite node.
+* `Slf4jSink`: Sends metrics to slf4j as log entries.
 
 Spark also supports a Ganglia sink which is not included in the default build due to
 licensing restrictions: