1. Apache Spark Lecture by: Faria Kalim (lead TA) CS425, UIUC
2012

2. Why Spark? Another system for big data analytics
Isn’t MapReduce good enough?
Simplifies batch processing on large commodity clusters

3. Expensive save to disk for fault tolerance

4. Why Spark? MapReduce can be expensive for some applications e.g.,
Iterative
Interactive
Lacks efficient data sharing
Specialized frameworks did evolve for different programming models
Bulk Synchronous Processing (Pregel)
Iterative MapReduce (Haloop) ….

5. Solution: Resilient Distributed Datasets (RDDs)
Immutable, partitioned collection of records
Built through coarse grained transformations (map, join …)
Can be cached for efficient reuse
Apply the same operations to many pieces of data

6. RDD
RDD
RDD
Read
HDFS
Cache
Read
Reduce
Map

7. Solution: Resilient Distributed Datasets (RDDs)
Immutable, partitioned collection of records
Built through coarse grained, ordered transformations (map, join …)
Fault Recovery?
Lineage!
Log the coarse grained operation applied to a partitioned dataset
Simply recompute the lost partition if failure occurs!
No cost if no failure

8. Cache Lineage RDD RDD RDD Read HDFS Read Map Reduce HDFS Read Map RDD

9. Cache Lineage RDD RDD RDD Read HDFS
RDDs track the graph of transformations that built them (their lineage) to rebuild lost data
Cache
Read
Map
Reduce
HDFS
Read
Map
Reduce
Lineage
RDD
RDD
RDD

10. What can you do with Spark?
RDD operations
Transformations e.g., filter, join, map, group-by …
Actions e.g., count, print …
Control
Partitioning
Persistence

11. Partitioning PageRank Links (url, neighbors) Ranks (url, ranks)
Joins take place repeatedly
Good partitioning reduces shuffles
Contributions
Ranks
(url, ranks)
Contributions

12. Generality RDDs allow unification of different programming models
Stream Processing
Graph Processing
Machine Learning …..

13. Gather-Apply-Scatter on GraphXB C D
Triplets
Vertices
Neighbors A B C D A B D C
Graph Represented In a Table

14. Gather-Apply-Scatter on GraphXB C D
Group-By A A B D C
Gather at A

15. Gather-Apply-Scatter on GraphXB C D
Map A B D C
Apply

16. Gather-Apply-Scatter on GraphXB C D
Triplets A B C
Join D A B D C
Scatter

17. Summary RDDs provide a simple and efficient programming model
Generalized to a broad set of applications
Leverages coarse-grained nature of parallel algorithms for failure recovery