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Cascalog: Clojure-based Query Language for Hadoop

I’ve already made the point that storing the data is just the start of the “adventure” and sooner than later you’ll have to put your NoSQL stored data to work.

Cascalog, introduced in the linked article, is a query language for Hadoop featuring:

  • Simple – Functions, filters, and aggregators all use the same syntax. Joins are implicit and natural.
  • Expressive – Logical composition is very powerful, and you can run arbitrary Clojure code in your query with little effort.
  • Interactive – Run queries from the Clojure REPL.
  • Scalable – Cascalog queries run as a series of MapReduce jobs.
  • Query anything – Query HDFS data, database data, and/or local data by making use of Cascading’s “Tap” abstraction
  • Careful handling of null values – Null values can make life difficult. Cascalog has a feature called “non-nullable variables” that makes dealing with nulls painless.
  • First class interoperability with Cascading – Operations defined for Cascalog can be used in a Cascading flow and vice-versa
  • First class interoperability with Clojure - Can use regular Clojure functions as operations or filters, and since Cascalog is a Clojure DSL, you can use it in other Clojure code.

While I do really like Clojure[1] and its conciseness, I kind of agree with the point Kevin Weil from Twitter made during the nosql:eu conference:

I need less Java in my life, not more

in the sense that higher level tools are more productive. And that’s the reason Twitter is using PIG (nb: I’d strongly recommend checking Kevin Weil’s slides) and Cloudera Hadoop distribution will include PIG and Hive.


  • [1] Disclaimer: I’m a Clojure absolute beginner though. ()