![Clojure examples
Clojure code Result
(+ 1 2 3) 6
(> 20 18) true
(defn incr [x] (+ 1 x)) 4
(incr 3)](https://image.slidesharecdn.com/cascalog-strange-loop-101021184759-phpapp01/85/Cascalog-at-Strange-Loop-6-320.jpg)
Cascalog at Strange Loop
- 1. Cascalog Data processing on Hadoop without the hassle Nathan Marz BackType @nathanmarz
- 2. What is Cascalog? Cascalog Variables and logic Abstraction Cascading Tuples, data workflows Key/value pairs, MapReduce aggregation
- 3. Cascalog’s components Cascading (the job execution engine) + Datalog (basis of the API design) + Clojure (the host programming language)
- 4. Clojure • General purpose programming language • Dialect of Lisp that compiles to Java bytecode
- 5. Clojure • “Programmable programming language”: Easy to build Domain Specific Languages (DSL) in Clojure
- 6. Clojure examples Clojure code Result (+ 1 2 3) 6 (> 20 18) true (defn incr [x] (+ 1 x)) 4 (incr 3)
- 7. Cascalog basics The “age” dataset
- 9. Cascalog basics Define and execute a query
- 10. Cascalog basics Where to emit results Define and execute a query
- 11. Cascalog basics Where to emit results Output variables Define and execute a query
- 12. Cascalog basics Where to “Predicates”: constrain emit results the output variables Output variables Define and execute a query
- 13. Predicates
- 15. Predicates Input fields Output fields
- 16. Predicates Fields can be constants or variables
- 17. Predicates Fields can be constants or variables Variables are prefixed with ? or !
- 18. Predicates
- 19. Predicates • Functions • Filters • Aggregators • Generators: finite sources of tuples
- 20. Example #1 Generator Filter
- 21. Example #2 Generator Function
- 22. Example #3 Generator Aggregator Filter
- 23. Join example
- 24. Join example Triggers a join
- 25. Join example
- 26. Join example Joins are an implementation detail
- 27. Demo time!
- 28. Why another query language for Hadoop? Existing tools cause too much Accidental Complexity
- 29. Accidental complexity Complexity caused by the tool used to solve a problem rather than the problem itself
- 30. Accidental complexity • Distinct query languages cause accidental complexity • Example: SQL injection
- 31. Query language • We want: • Ability to abstract • Ability to compose
- 32. Abstraction Clojure function that returns a subquery
- 33. Abstraction Defining and using custom operation
- 34. Composability Dynamic query with parameterized operation
- 36. Composability expands to Using a predicate macro
- 37. Contrast to Pig “Average” is 300 lines of code in Pig
- 38. Optimized aggregators in Cascalog Implementation of count and sum
- 39. Why another query language for Hadoop? Existing tools cause too much Accidental Complexity
- 42. Composability For each id: select value with the biggest timestamp Value normalization algorithm
- 45. Try Cascalog yourself! Project Page http://www.github.com/nathanmarz/cascalog Introductory Tutorial http://nathanmarz.com/blog/introducing-cascalog/ 5 minutes to install Clojure, Hadoop, and Cascalog locally! See project README
- 46. BackType is hiring Think Cascalog’s cool? Come build amazing software at BackType. http://www.backtype.com/jobs
- 47. Questions? Follow me on Twitter at @nathanmarz nathan.marz@gmail.com