Mortar is a platform-as-a-service for Hadoop. With Mortar, you can run jobs on Hadoop using Apache Pig and Python without any special training. You create your project using the Mortar Development Framework, deploy code using the Git revision control system, and Mortar does the rest.

The data we're using comes from About DocGraph headed up by Fred Trotter You must have access to the DocGraph dataset in order to run this example.

This example also relies on the National Provider Standard Identifier (NPI) file located here and the National Uniform Claim Committee (NUCC) Health Care Provider Taxonomy Code Set located here.

This project is based on a more generic Mortar developed project that you can find at Mortar's Github page.

This Mortar project calculates pageranks for the DocGraph data set. To run this example:

1. Obtain an Amazon S3 account

2. Signup for a Mortar account

3. Install the Mortar Development Framework

4. Clone this repository to your computer and register it as a project with Mortar:

    git clone git@github.com:davidfauth/DocGraph-Page-Rank.git
    cd DocGraph-Page-Rank
    mortar register DocGraph-Page-Rank
   

5. Configure the data sources. In controlscripts/pagerank.py, modify the #Input Data Paths to reflect the location of your data files.

Once everything is set up you can run this example by doing:

    mortar run docGraphPagerank --clustersize 5

By default this script will run on the full DocGraph data set with the most followers and finish in about 1 hour a minutes using a 5 node cluster.

Pagerank simulates a random walk over a graph where each follower-followed relationship is an edge. The pagerank of a user is the probability that after a large number of steps (starting at a random node) the walk will end up at the user's node. There is also a chance at each step that the walk will "teleport" to a completely random node: this added factor allows the algorithm to function even if there are "attractors" (nodes with no outgoing edges) which would otherwise trap the walk.

Pagerank is an iterative algorithm. Each pass through the algorithm relies on the previous pass' output pageranks (or in the case of the first pass a set of default pageranks generated for each node). The algorithm is considered done when a new pass through the data produces results that are "close enough" to the previous pass. See http://en.wikipedia.org/wiki/PageRank for a more detailed algorithm explanation.

The file ./controlscripts/pagerank.py is the top level script that we're going to run in Mortar. Using Embedded Pig this Jython code is responsible for running our various pig scripts in the correct order and with the correct parameters.

For easier debugging of control scripts all print statements are included in the pig logs shown on the job details page in the Mortar web application.

The control scripts contain references to data stored on your personal Amazon S3 buckets. These will need to be changed for the job to run correctly. These are located in the #Input Data Paths section.

This project contains four pig scripts:

This pig script takes the full DocGaph graph and returns the subset of the graph that includes only the top 750 doctors/hospitals/labs.

This pig script takes our input data and converts it into the format that we'll use for running the iterative pagerank algorithm. This script is also responsible for setting the starting pagerank values for each user.

This pig script calculates updated pagerank values for each user in the DocGraph graph. It takes as input the previous pagerank values calculated for each user. This script also calculates a 'max_diff' value that is the largest change in pagerank for any user in the graph. This value is used by the control script to determine if its worth running another iteration to calculate even more accurate pagerank values.

This pig script takes the final pagerank values calculated for each user and writes the top 750 users and their pageranks to S3.

The damping factor determines the variance of the final output pageranks. This is a number between 0 and 1 where (1 - DAMPING_FACTOR) is the probability of the random walk teleporting to a random node in the graph. At 0 every node would have the same pagerank (since edges would never be followed). Setting it to 1 would mean the walks get trapped by attractor nodes and would rarely visit nodes with no incoming edges. A common value for the damping factor is 0.85.

Pagerank is an iterative algorithm where each run uses the previous run's results. It stops when the maximum difference of a user's pagerank from one iteration to the next is less than the CONVERGENCE_FACTOR.