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Danger
Grading Penalties
The following table outlines the violations of the project rules and their corresponding grade penalties for this project.
Violation Penalty of the project grade
Using more than $35 of AWS resources -10%
Using more than $50 -100%
Not tagging any of your resources -10%
Using any Project tags apart from Project:4.2 -10%
Using GraphX for either in Tasks 1 or 2 -100%
Submitting your AWS credentials, other secrets, or Andrew Id in your code for
grading
-100%
General Suggestions
General Suggestions
Read the Scala and Spark primers before attempting this project.
Spark programs can be written in Python, Scala and Java. However, we suggest you choose your language wisely in
the project. Some facts you should consider:
Spark is written in Scala. Scala has the most comprehensive support and Spark programs written in Scala
perfectly reflects the Spark way of thinking.
Python code is easy to deploy in Spark (you dont need to worry much about dependencies, jar build, etc), but it
can be too slow for you to get the bonus.
GraphX (which you will be using in Task 3) only has Scala API for the time being.
Spark has a Web UI that you may find useful for troubleshooting cluster problems and job failure. See Monitoring and
Instrumentation: Web Interfaces (http://spark.apache.org/docs/latest/monitoring.html#web-interfaces) for details.
Do not use one RDD action when it is not necessary. Once you call an action, a job is created. Spark will run a
computation on your distributed dataset and return one value back to the driver. For example, many students from last
semester who encountered out-of-memory problems were trying to copy a big RDD to the driver.
someBigRdd.collect()
You may notice one container fails and then the rest fail one by one. Think of the reason why this happens.
You should realize that shuffle operations are expensive. Shuffle operations will add a burden to your disk I/O, data
serialization, network I/O and memory pressure (from garbage collection)! For example, joinis one of the most
expensive operations. You will realize how long it takes in the webUI if you have it in your application.
Wisely choose your transformation method. For example, if you want to sort an RDD by value, you can use sortBy ,
but not invert Key and Value first, then use sortByKey .
We strongly recommend you being becoming familiar with some basic operations before writing any code.
Use reduceByKey() instead of groupByKey() when possible. For a simple word count example, below are two
approaches which will have a large difference in performance. Try to find out the reason. Hint: remember the combiner
in the MapReduce project?
example:
http://spark.apache.org/docs/latest/monitoring.html#web-interfaces
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rdd.flatMap(x => x.split( )).map(x => (x, 1)).reduceByKey(_ + _)
rdd.flatMap(x => x.split( )).map(x => (x, 1)).groupByKey().map(t => (t._1, t._2.sum))
Do not cache your RDDs everywhere. Cache RDDs when necessary.
Partitions are basic units of parallelism in Spark. Use repartition when it is necessary (one partition is created for each
block of the file in HDFS). You should realize the number of partitions of your RDD. Having too many or too few
partitions is a problem.
If you are using some static or global data structure for some reason, try to broadcast that variable. Be careful,
global variable that are big will also lead to OOM problems.
Task 1
Scenario
You have built a successful search engine, but no one seems to be using it. You try to spread the word by asking all your
2773 Facebook friends and 32 Twitter followers to use the Mellon Search Input Text Predictor (MSITP).
Unfortunately, this doesnt work. After one week, only 7 people have used your website. You realize that, for it to be a
success, you need to showcase your service to highly influential people who are easily impressed Twitter celebrities!
Figure 1: Twitters network is dominated by a small number of influential people, and a large number of silent observers
You encounter a dataset and some research by Kwak [1], describing the analysis of a network of Twitter users. Some further
digging reveals the PageRank algorithm for identifying influential nodes in a network. You download the dataset and decide
to use your MapReduce skills to run PageRank and find the influential nodes to target.
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Unfortunately, many network analysis and machine learning algorithms rely on multiple iterations of execution. This is where
MapReduce works poorly after each iteration of Map and Reduce, it spills all the data to disk and spends a lot of time
saving and loading the data.
Fortunately, the Cloud Computing course introduces you to Spark at exactly the right time. Spark is optimized for iterative
jobs, by enabling the capability of storing intermediate results in memory. In this module, you will be introduced to Spark
through an increasingly harder set of tasks, and use it to perform PageRank on the dataset of Twitter users to find the
influencers. Afterwards, you will implement a second degree centrality algorithm using Sparks GraphX.
[1] [Kwak, H., Lee, C., Park, H., & Moon, S. (2010, April). What is Twitter, a social network or a
news media?. In Proceedings of the 19th international conference on World wide web (pp.
591-600). ACM](http://law.di.unimi.it/webdata/twitter-2010/)
Tasks and Instructions
We are going to use the Apache Spark framework to run a few graph computations on the Twitter social graph. The dataset
details are as follows:
Table 1: Dataset for this project
File Name Location Size
Graph s3://cmucc-datasets/p42/Graph 10.4GB
Use aws s3 cpor wgetto get our data and files from our S3 bucket.
The graph is stored as an edge list format. This provides the list of source and destination vertices for each edge of the
graph. Each node represents a user in the Twitter social network and an edge (u, v) means user u follows user v in Twitter. For
your convenience, the first 10 lines of the file are listed below (Note fields are separated by t ).
55103430913
55103506997
55104289028
551011752536
551013433256
551014380596
551017413259
551025643118
551026929986
551030403395
Task 1: Getting Started with Spark and the Social Graph
Dataset
The first task is for you to get familiar with Spark. We will ask you to find the number of edges and vertices in the Twitter
social graph, as well as the number of followers of each user. The edges in the graph are directed, so if there are edges (u, v)
and (v, u), you should count them as two edges.
We will explore two different ways of working with Spark: using Spark Shell, and submitting Spark programs.
Spark Shell
You should count the number of edges and vertices by running commands in the Spark Shell (either Scala spark-
shellor Python pyspark ). You will find this interactive REPL way is very useful for iterative data processing. You
need to put the result you get in a file called answerto get points.
Spark programs
You will need to achieve the same goal by using two different APIs, RDDs and Dataframe. In your two spark
programs, you need to count the number of followers for each user, and sort by the number of followers. Note you will
need to run our submitter to run your Spark programs.
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As mentioned in the Spark primer, dataframe uses Catalyst (https://spark-summit.org/2016/events/deep-dive-into-
catalyst-apache-spark-20s-optimizer/) to optimize code. Typically dataframe and dataset programs with Catalyst will
run faster than RDDs. But in this task, because loading text file into a dataframe needs more time than RDDs, you may
not see a big difference in performance when using these two APIs. From our testing result, dataframe is 2-10 times
faster than RDDs (without loading).
You can use System.nanotimeto print out your program execution time to see how fast dataframe is.
Building your project
If you choose to use maven, you can find the pom.xml file for this project here: s3://cmucc-
public/s17/p42/ScalaSparkMavenTemplate.zip .
If you choose to use sbt, you can find the build.sbt file for this project here: s3://cmucc-public/s17/p42/build.sbt`.
Information
Steps to complete this task and submit
1. Make sure you use EMR 5.4.0 (check the Spark primer for details). There is no limitation on the instance type and
number in this task.
2. Download the submitter from s3://cmucc-public/s17/p42/submitter1.tgzon the master node of your Spark
cluster.
3. Run the Spark commands in shell mode to complete counting vertices and edges.
4. Enter the numbers you got from your shell run in the file answer .
5. The RDD program should produce output in the following format for the entire Twitter social graph:
[user_id]t[num_followers]
Only store the top 100 records in hdfs:///followerRDD-output . Your code should directly store your output
into that path. Our submitter will look for RDD output in this path.
6. In the dataframe program, the final dataframe should be in this format( use show()):
+++
|followee|count|
+++
|21513299| 27|
|23934131| 18|
|23933986| 15|
|23934048| 15|
|21448831| 14|
|23933989| 12|
+++
Save the top 100 records of this dataframe as a parquet file, in hdfs:///followerDF-output .
Use df.write.format(parquet).save(hdfs:///followerDF-output)for Scala. Use
df.write.save(hdfs:///followerDF-output, format=parquet)for Python.
7. If you write a Python script, please exactly name your RDD script followerRDD.pyand dataframe script
followerDF.py . If you implement in Java or Scala, name RDD and dataframe class as FollowerRDDand
FollowerDF , compile as one jar package, name it exactly p42.jar .
8. Our submitter will run the following command in the home directory to run your Spark program. Please make sure
you can run it without errors before you run the submitter. For Python developers:
spark-submit followerRDD.py
spark-submit followerDF.py
For Java and Scala developers:
spark-submit class FollowerRDD p42.jar
spark-submit class FollowerDF p42.jar
https://spark-summit.org/2016/events/deep-dive-into-catalyst-apache-spark-20s-optimizer/
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9. You should not merge your output files, our submitter will take care of that.
10. Make sure to copy ALL the shell scripts and source code (.py, .java and .scala files) into the srcfolder.
11. Modify the referencefile and note down all the help you got from the Internet and from other students.
12. Once you are confident about your code, you can first chmod +x submitter1and run ./submitter1 .
Task 2
Task 2: Rank Each User by Influence
Let us now run an iterative computation on the Twitter social graph. For this task, you will rank each user by their influence.
The problem is to find the influential or important nodes. Given a graph, which node is more important?
Figure 2.1: Toy graph for PageRank calculation.
We solve the problem by using the PageRankalgorithm. PageRank is a type of a random walk algorithm. Imagine there is an
agent walking on a graph. The agent can randomly jump from one node to another node over the edges in the graph. The
agent tirelessly walks the graph. At the end of the day, influential nodes are the ones that were frequently visited by the agent.
Similarly, the PageRank algorithm finds the score for each node iteratively. When the score of every node does not change
across iterations, we refer to it as the algorithm converges . When it converges, the final score of each node represents the
probability of being visited by the agent. Therefore, the bigger the score is, the more influential the node is .
PageRank is a type of random walkalgorithm.
For this task, we will use the following algorithm to update the rank of a vertex in a graph:
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Figure 2.2: Overview of the PageRank Algorithm.
As shown in Figure 2.5, we can calculate the PageRank score iteratively. There are 2 ways to implement Step 3 in Figure 2.5:
matrix solverand for-loopsolver. In this task, you are required to implement your PageRank algorithm by for-loop
solver .
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Figure 2.3: PageRank Matrix Solver.
Figure 2.4: PageRank For-loop Solver.
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Figure 2.5: PageRank Convergence Analysis.
PageRank Implementation Rules
Initial Rank Values. The initial value of the rank of each user should be 1/n . This value needs to be assigned to every
vertex, so its easy to think of this as being a mapoperation.
Damping Factor. There are many possible values for the damping factor, and in this task we set it to 0.85 .
Output Format. You must ensure that the output of your PageRank function matches the same syntax of the input, so
that the algorithm can iteratively compute the ranks.
Dangling Users. You need to handle the case of dangling nodes (nodes with zero out-degrees). The weight of the
dangling users must be redistributed across all the users during each iteration (see Figure 2.2). Remember, the sum of
all PageRank scores should always be 1 in each iteration.
To help you understand the algorithm, you can find more examples in this pdf
(https://s3.amazonaws.com/15619public/webcontent/pagerank_examples.pdf).
Information
Steps to complete this task and submit
1. Make sure you use EMR 5.4.0 .
2. If you want to submit your code, you have to launch 5 r3.xlarge core instances.
3. Download the submitter from s3://cmucc-public/s17/p42/submitter2.tgzon the master node of your Spark
cluster.
4. Write a Spark program that computes the PageRank value for each node in the Twitter social graph. Your program
should follow the implementation rules described above and produce the following output for the entire graph by
running 10iterations of the computation.
[user_id]t[PageRank_value]
https://s3.amazonaws.com/15619public/webcontent/pagerank_examples.pdf
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5. If you write a Python script, please name your script exactly pagerank.py . If you implement in Java or Scala,
name your jar package exactly p42.jarand the main class should be PageRank .
6. Please make sure you can run it without errors before you run the submitter.
7. Our submitter will look for output in hdfs:///pagerank-output .
8. Again, do not merge and sort your output files, our submitter will take care of that.
9. Make sure to copy all the source code (.py, .java and .scala files) into the srcfolder.
10. Modify the referencefile and note down all the help you got from the Internet and from other students.
11. Once you are confident about your code, you can run chmod +x submitter2and run the
submitter: ./submitter2 .
Bonus Task: Speed up Spark!
Chances are that it might take hours to run the 10-iteration PageRank on Spark. After you have passed the correctness
check, it is time to speed it up! We want you to look into advanced topics of Spark to shorten your execution time of
PageRank to less than 30 minutes. Note that you can get the bonus only if you got full marks in Task2.
Here are some suggestions you can try to improve the performance of your program:
Review our general suggestions above.
Do some research about the programming languages in Spark.
Improve your code. Develop a better understanding of RDD manipulations. Understand the lazy transformation in
Spark. Think carefully of whether and when you should use operations of cache() , collect() , persist()and
unpersist() . Check Spark Programming Guide: RDD Persistence
(https://spark.apache.org/docs/latest/programming-guide#rdd-persistence) to learn more.
Monitor your instances to make sure they are fully utilized. You can enable detailed CloudWatch monitoring on each
instance in your Spark cluster. Metrics of disk and network I/O are captured, which can help you decide if you need
more compute resources in your cluster. Alternatively, you could choose to use htop, and utilities like iotop and iostat.
Spark is a tunable framework where there are many parameters that you can configure to make the best use of the
resources you have. You might want to understand the meaning of parameters such as spark.driver.memory ,
spark.executor.memory , spark.executor.cores , and spark.python.worker.memory . Check Spark
Configuration (http://spark.apache.org/docs/latest/configuration.html) to learn more and configure your Spark cluster
to achieve better performance.
Notice that RDDs are read-only and your PageRank program iterates 10 times, so there can be many orphan
intermediate RDDs or garbage. Thinking about garbage collection can contribute a lot to performance improvement.
The parameters of spark.memory.fractionand spark.memory.storageFractionare closely related to this topic.
For more references, check Tuning Spark: Garbage Collection Tuning
(https://spark.apache.org/docs/latest/tuning#garbage-collection-tuning).
Using accumulators (http://spark.apache.org/docs/latest/programming-guide.html#accumulators) is a good way to
count or sum throughout different nodes.
Be careful to use repartitionon your RDD. It might improve your CPU utilization, but this transformation always
shuffles all data over the network. This will increase the amount of work the Spark engine has to do. Another way is to
set spark.default.parallelismto change the default partition number of an RDD. Dont change the default
number until you know what you are doing. Learn more about RDD partitioning, and choose the best strategy. You can
use rdd.partitions.size (Scala) to check the partition number of an RDD.
Information
How to submit the bonus task
Please use EMR 5.4.0 as you did in the previous tasks.
Please use the same submitter you used for the PageRank task. Download and run the submitter on your master node.
Follow the same instructions from last task to run your application. Once your performance is better than 1800s (30
min), you can get a bonus up to 10%! (If you simply get below 1800s (30 min) you will earn a 10% bonus. Bonus only
applies if you already got full points in Task 2.)
Note: We are not done yet! Dont forget to do the AssessMe and unlock Task 3. It is worth 20% of this project. Moreover, the
only choice for Task 3 is Scala because thats all GraphX supports for the time being.
https://spark.apache.org/docs/latest/programming-guide#rdd-persistence
http://spark.apache.org/docs/latest/configuration.html
https://spark.apache.org/docs/latest/tuning#garbage-collection-tuning
http://spark.apache.org/docs/latest/programming-guide.html#accumulators
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Task 3
Task 3: Graph Processing using GraphX
In the previous tasks, you gained some experience with using Spark to write an iterative program. The PageRank algorithm
you implemented performs several iterations on the graph to analyze the links and compute the PageRank score of each
node. During each iteration, a node will need values from all the neighbors. This nature of PageRank makes it perfectly fit into
the graph-parallel model. In fact, there are graph processing frameworks that were developed to help us do this kind of
analytics. These frameworks include GraphLab (developed at CMU) ,GraphX (a part of Apache Spark), and others.
In this task, you will use GraphX to do further analysis based on your PageRank results. Dont worry if you didnt (yet) do well
in Task 2. You are allowed to use GraphXs built-in pagerank()to calculate the PageRank result, so that you can get full
points in Task 3 regardless of your score in Task 2. Be careful, if you use GraphXs built-in pagerank() function for Task 2,
you will incur a 100% penalty.
By completing this task, you will gain experience in developing graph-parallel programs and a deeper understanding of the
advantage of adopting the graph-parallel programming model to deal with iterative applications where the data is highly
dependent.
GraphX
GraphX is a component in Spark for graphs and graph-parallel computation. Spark users will find it familiar and easy to get
started in because in GraphX a graph is constructed by two RDDs: edges and vertices. Also, properties of arbitrary types can
be attached to each edge and each vertex (for us to analyze).
GraphX provides a set of basic graph operators, such as numVertices , numEdges , degrees , subgraph , joinVertices ,
etc. A complete list of operators can be found in GraphX Programming Guide (https://spark.apache.org/docs/latest/graphx-
programming-guide#summary-list-of-operators). Apart from the basic graph operations, there are generalized and powerful
operations like aggregateMessagesand pregelthat you can use to build graph processing solutions for a variety of
problems ( pregelis an optimized variant of the Pregel
(https://www.cs.cmu.edu/~pavlo/courses/fall2013/static/papers/p135-malewicz.pdf) API). In addition, GraphX includes a
growing collection of specialized graph algorithms and builders to simplify graph analytics tasks. As an example, you will find
that there is a pagerankimplementation in GraphX.
Task Description
In this task, you will learn how to use aggregateMessagesto perform graph-parallel analytics on a large dataset. We will
continue to use the same Twitter graph dataset. In addition, we are going to add properties to the graph based on your
PageRank result.
The 2nd-degree influential scorecalculates a type of centrality scorefor a node, i.e. how influentialis a
node in the graph. PageRank score is a type of centrality scorewhich mainly considers the directional 1st-degree edges
of a node. For example, the following graph (though node 4 is not possible in the Graph of this project) has 5 nodes, and
what are their final PageRank scores?
https://spark.apache.org/docs/latest/graphx-programming-guide#summary-list-of-operators
https://www.cs.cmu.edu/~pavlo/courses/fall2013/static/papers/p135-malewicz.pdf
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Figure 3.1: Toy graph for calculating the centrality score
The converged PageRank score for node 0 to 4 are [0.036, 0.4402, 0.451, 0.036, 0.036]. As expected Node 1 and 2 are the
most important nodes. But node 4 has the same score with node 0 and 3. Do you think it is reasonable? One might argue
that Node 0 seems to be more important than Node 4 because it has a few connections to central nodes (Node 2 and Node
1). We can fix the PageRank score by considering the 2nd-degree influential scoredescribed in this section.
High-level instructions for you to approach this task are illustrated as in Figure 3.2 and described as follows:
Make sure you have the two input datasets (graph and properties). If you think your PageRank result is flawed, feel free
to use GraphXs pagerankto generate the data. But remember, GraphX is not allowed in Task 2! Some may notice
that GraphX doesnt give the same values for each user, but that wont affect your scores for this task.
Create a graph by loading the graph edge list dataset.
Attach the influence values of each user to the corresponding vertex. This can be done by a graph join operation
between the graph and the properties dataset.
Now you should have a property graph that each node has its influence value. To continue, for each user, find the most
influential person he/she follows. Hints: you may want use aggregateMessageshere and attach (join) this
intermediate result to the graph so that the next step can perform aggregateMessagesagain. This is called iterative
processing!
Now you should have a new property graph that each node knows its most influential followee. Based on this result,
for each user, find the most influential person his/her followees follow. Save this result to an output file.
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Figure 3.2: Find the most influential user within a distance of 2
In Figure 3.2, we initially have a property graph (each vertex has been attached an influence value). In the first round, A1, A2
send their values to A. B1, B2 send their values to B. C1, C2 send their values to C. A, B, C also need to send their values to
O. Then A, B, C, and O will aggregate (reduce) the value they receive to find the max (to be sent later). Note, for the vertices
that do not receive values (like A1), the max value is 0. In the second round, A, B, C each sends its max value to O. Then O
will aggregate (reduce) to find the max.
In this task, we are going to use the formula below to calculate the new score for one user.
new_influencial_score = 0.5 * pagerank_score + 0.5 * most_influential_second_degree_user_score
For example, If the PageRank score of Node O in Figure 3.2 is 0.02, and the maximum PageRank score of Os 2nd-degree
neighbors is 0.01, then Os final score is (0.02+0.01)/2=0.015.
Neighborhood Aggregation
Unlike most other graph operators in GraphX, aggregateMessagesis a general purpose mechanism to enable parallel
computation on a property graph. You will find other operators in the GraphX source code
(https://github.com/apache/spark/blob/master/graphx/src/main/scala/org/apache/spark/graphx/GraphOps.scala) are actually
implemented gracefully using aggregateMessages , such as collectNeighborIdsand degrees . Here is a short
explanation of how it works: 1) for each edge (or strictly speaking, triplet, using GraphXs terminology), send some sort of
messages to one or both of its two ends this step is like a map ; 2) For each vertex, process all the messages it gets from its
connecting edges this step is like a reduce . See the GraphX Programming Guide: Neighborhood Aggregation
(https://spark.apache.org/docs/latest/graphx-programming-guide#neighborhood-aggregation) for details.
The signature of aggregateMessagesis
https://github.com/apache/spark/blob/master/graphx/src/main/scala/org/apache/spark/graphx/GraphOps.scala
https://spark.apache.org/docs/latest/graphx-programming-guide#neighborhood-aggregation
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class Graph[VD, ED] {
def aggregateMessages[Msg: ClassTag](
sendMsg: EdgeContext[VD, ED, Msg] => Unit,
mergeMsg: (Msg, Msg) => Msg,
tripletFields: TripletFields = TripletFields.All)
: VertexRDD[Msg]
}
As revealed in the signature, the function will return an RDD of Msgtype, which is a generic type and represents the type of
the messages you send. To help you understand how to send and aggregate messages, lets take a look at the degree
calculation of an undirected graph as an example.
graph.aggregateMessages(
ctx => { ctx.sendToSrc(1); ctx.sendToDst(1) },
_ + _
)
The code is very succinct. Since this is an undirected graph, every edge contributes 1 to the degree of both of its ends. So
we send message 1to both vertices, and then sum the ones up on each vertex of the whole graph to get the degree RDD.
Information
Steps to complete this task and submit
1. Make sure you use EMR 5.4.0 . No limitation on instance type and number in this task.
2. Download the submitter from s3://cmucc-public/s17/p42/submitter3.tgzon the master node of your Spark
cluster.
3. Write a Spark GraphX program to compute second degree centrality for each user in the Twitter social graph. Your
program should follow the implementation rules described above and produce the following output for the entire
graph.
[user_id]t[most_influential_second_degree_user_id]t[new_user_influencial_score] ?
Note: If no user is found (e.g. I am not following anyone), assume a user with id=0 and influence=0.0 when you
aggregate messages.
4. Name your jar package exactly p42.jarwith a main class called Task3 .
5. Please make sure you can run it without errors before you run the submitter.
6. Our submitter will look for output in hdfs:///task3-output .
7. Again, do not merge and sort your output files, our submitter will take care of that.
8. Make sure to copy all of the source code (for this task, .scala files) into the srcfolder.
9. Modify the referencefile and note down all the help you got from the Internet and from other students.
10. Once you are confident about your code, you can run chmod +x submitter3and run the
submitter: ./submitter3 .
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