Notes: http://goo.gl/9dDnq Before we begin, a disclaimer... • Launched the rebuild mid Jan 2013. • Not running at scale, yet; 1000 users. • You’re about to see our strategy for scale. We think it’s a good one :-) • I’d like to do a follow-up at ScaleConf 2014 and share how things are going! Friday 19 April 13
Notes: http://goo.gl/9dDnq About our startup • Started Cognician with Barry and Patrick Kayton in early 2010 • Proved the concept over 18 months with good old LAMP and Adobe Flex/AIR • Started V2 app rebuild with Google Closure Javascript late 2011 Friday 19 April 13
Notes: http://goo.gl/9dDnq So, why Clojure? • In April 2012, after several months and 11,000 lines of (soul-crushingly verbose) Javascript development, discovered Clojure • Rewrote the model portion of this new app in two weeks and 1500 lines of Clojure • Evaluated it for back end, and decided to go all-in! Friday 19 April 13
Notes: http://goo.gl/9dDnq Clojure •Modern Lisp dialect •General purpose functional language •Immutable data structures •JVM, Javascript, CLI, and more Friday 19 April 13
Notes: http://goo.gl/9dDnq Datomic is a database of flexible, time-based facts, supporting queries and joins, with elastic scalability, and ACID transactions. Friday 19 April 13
Notes: http://goo.gl/9dDnq How Datomic models data • Entity-attribute-value tuples, or ‘datoms’ • Entities are really just IDs • Any mix of attributes can be put on any entity • Schema defines what attributes can do • Entity relations are just a type of attribute Friday 19 April 13
Notes: http://goo.gl/9dDnq How Datomic models time • Novelty enters as transactions, of • Assertions and retractions of datoms • Every datom linked to its transaction • Every transaction is timestamped • So, it’s actually EAVT, a.k.a. facts! Friday 19 April 13
Notes: http://goo.gl/9dDnq Query with Datalog ; find all entity ids that have an email address [:find ?entity :where [?entity :user/email]] Friday 19 April 13
Notes: http://goo.gl/9dDnq Query with Datalog ; find all entity ids that have an email address [:find ?entity :where [?entity :user/email]] ; find a user id and password for a given email address [:find ?user ?password :where [?user :user/email "[email protected]"] [?user :user/password ?password]] Friday 19 April 13
Notes: http://goo.gl/9dDnq Query with Datalog ; find all entity ids that have an email address [:find ?entity :where [?entity :user/email]] ; find a user id and password for a given email address [:find ?user ?password :where [?user :user/email "[email protected]"] [?user :user/password ?password]] ; find all the users in all the groups I belong to [:find ?user :in $ ?me [?me :user/groups ?group] [?user :user/groups ?group]] Friday 19 April 13
Notes: http://goo.gl/9dDnq In Summary • Event-sourcing and immutable data are a great match • Clojure code is concise and easier to reason about (and has a lot of parenthesis) • Datomic cuts out a lot of the hassle in building scalable, distributed systems Friday 19 April 13
Notes: http://goo.gl/9dDnq Cape Town Clojure User Group •Next meet: 18 May 2013 •Venue: Codebridge in Claremont •Intro to Clojure session •Talks on Datomic, ClojureScript, etc •Details in the notes: http://goo.gl/9dDnq Friday 19 April 13
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