Docs describing Spark monitoring and instrumentation

docs/_layouts/global.html

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                                 <li><a href="configuration.html">Configuration</a></li>
+                                <li><a href="monitoring.html">Monitoring</a></li>
                                 <li><a href="tuning.html">Tuning Guide</a></li>
                                 <li><a href="hardware-provisioning.html">Hardware Provisioning</a></li>
                                 <li><a href="building-with-maven.html">Building Spark with Maven</a></li>

docs/monitoring.md

+---
+layout: global
+title: Monitoring and Instrumentation
+---
+
+There are several ways to monitor the progress of Spark jobs.
+
+# Web Interfaces
+When a SparkContext is initialized, it launches a web server (by default at port 3030) which 
+displays useful information. This includes a list of active and completed scheduler stages, 
+a summary of RDD blocks and partitions, and environmental information. If multiple SparkContexts
+are running on the same host, they will bind to succesive ports beginning with 3030 (3031, 3032, 
+etc).
+
+Spark's Standlone Mode scheduler also has its own 
+[web interface](spark-standalone.html#monitoring-and-logging). 
+
+# Spark Metrics
+Spark has a configurable metrics system based on the 
+[Coda Hale Metrics Library](http://metrics.codahale.com/). 
+This allows users to report Spark metrics to a variety of sinks including HTTP, JMX, and CSV 
+files. The metrics system is configured via a configuration file that Spark expects to be present 
+at `$SPARK_HOME/conf/metrics.conf`. A custom file location can be specified via the 
+`spark.metrics.conf` Java system property. Spark's metrics are decoupled into different 
+_instances_ corresponding to Spark components. Within each instance, you can configure a 
+set of sinks to which metrics are reported. The following instances are currently supported:
+
+* `master`: The Spark standalone master process.
+* `applications`: A component within the master which reports on various applications.
+* `worker`: A Spark standalone worker process.
+* `executor`: A Spark executor.
+* `driver`: The Spark driver process (the process in which your SparkContext is created).
+
+The syntax of the metrics configuration file is defined in an example configuration file, 
+`$SPARK_HOME/conf/metrics.conf.template`.
+
+# Advanced Instrumentation
+Several external tools can be used to help profile the performance of Spark jobs:
+
+* Cluster-wide monitoring tools, such as [Ganglia](http://ganglia.sourceforge.net/), can provide 
+insight into overall cluster utilization and resource bottlenecks. For instance, a Ganglia 
+dashboard can quickly reveal whether a particular workload is disk bound, network bound, or 
+CPU bound.
+* OS profiling tools such as [dstat](http://dag.wieers.com/home-made/dstat/), 
+[iostat](http://linux.die.net/man/1/iostat), and [iotop](http://linux.die.net/man/1/iotop) 
+can provide fine-grained profiling on individual nodes.
+* JVM utilities such as `jstack` for providing stack traces, `jmap` for creating heap-dumps, 
+`jstat` for reporting time-series statistics and `jconsole` for visually exploring various JVM 
+properties are useful for those comfortable with JVM internals.