anchor.diff:  
   NOTE: This model of graph computing was made popular by Google's link:http://googleresearch.blogspot.com/2009/06/large-scale-graph-computing-at-google.html[Pregel] graph system. In the open source world, this model is found in OLAP graph computing systems such as link:https://giraph.apache.org/[Giraph], link:https://hama.apache.org/[Hama], and link:http://faunus.thinkaurelius.com[Faunus].
   
  -[[mapreduce-extensions]]
  -MapReduce Extensions
  ---------------------
  +[[mapreduce]]
  +MapReduce
  +---------
   
   The BSP model proposed by Pregel stores the results of the computation in a distributed manner as properties of the vertices in the graph. However, in many situations, it necessary to aggregate those resultant properties into a single result set (i.e. a statistic). For instance, assume a VertexProgram that computes a nominal cluster for each vertex. At the end of the computation, each vertex will have an hidden property denoting the cluster it is in. In order to answer the following questions, MapReduce jobs are required:
   
  
positive.code: Gremlin Utilities
  =================
  
  Gremlin Console
  ---------------
  
  
negative.code: The `GiraphGraphComputer` makes use of a properties file much like any other `GraphComputer`. However, given the relationship to Hadoop which is property heavy, it is important to look at a particular properties file. The properties file below is located at `conf/giraph-kryo.properties'.
  
  [source,text]
  gremlin.inputLocation=tinkerpop-classic-vertices.gio
  giraph.vertexInputFormatClass=com.tinkerpop.gremlin.giraph.structure.io.kryo.KryoVertexInputFormat
  gremlin.outputLocation=output
  giraph.vertexOutputFormatClass=com.tinkerpop.gremlin.giraph.structure.io.kryo.KryoVertexOutputFormat
  gremlin.sideEffectOutputFormatClass=org.apache.hadoop.mapreduce.lib.output.SequenceFileOutputFormat
  gremlin.vertexProgram=com.tinkerpop.gremlin.process.computer.traversal.TraversalVertexProgram
  gremlin.traversalVertexProgram.traversalSupplierClass=com.tinkerpop.gremlin.giraph.process.graph.example.TraversalSupplier1
  gremlin.jarsInDistributedCache=true
  gremlin.deriveComputerSideEffects=false
  giraph.minWorkers=2
  giraph.maxWorkers=2
  
  A review of the properties above are presented in the table below.
  
  [width="100%",cols="2,10",options="header"]
  |=========================================================
  |Property |Description
  |`gremlin.inputLocation` |The location of the input file(s) for Giraph to read the graph from.
  |`giraph.vertexInputFormatClass` |The format that the graph input file(s) are represented in.
  |`gremlin.outputLocation` |The location to write the computed Giraph graph to.
  |`giraph.vertexOutputFormatClass` |The format that the output file(s) should be represented in.
  |`gremlin.sideEffectOutputFormatClass` |The format of any resultant GraphComputer SideEffects.
  |`gremlin.vertexProgram` |The `VertexProgram` to distribute to all vertices in the `GiraphGraph`
  |`gremlin.traversalVertexProgram.traversalSupplierClass` |For `TraversalVertexProgram`, the location of the Gremlin traversal to use (if not using Gremlin Console).
  |`gremlin.jarsInDistributedCache` |Whether to upload the Giraph-Gremlin jars to Hadoop's distributed cache (necessary if jars are not on machines' classpaths).
  |`gremlin.deriveComputerSideEffects` |Whether or not `SideEffects` are yielded (requires an extra MapReduce job if true).
  |`giraph.minWorkers` |The minimum number of parallel workers to execute the vertices of the graph.
  |`giraph.maxWorkers` |The maximum number of parallel workers to execute the vertices of the graph.
  |=========================================================
  
  IMPORTANT: The maximum number of workers can be no larger than the number of map-slots in the Hadoop cluster minus 1. For example, if the Hadoop cluster has 4 map slots, then `giraph.maxWorkers` can not be larger than 3. One map-slot is reserved for the master compute node and all other slots can be allocated as workers to execute the `VertexProgram`s on the vertices of the graph.
  
  