The document introduces CouchDB, an open-source document-oriented database. It notes that CouchDB uses a document model with JSON documents and map-reduce functions. It also discusses three main reasons for considering CouchDB - its focus on availability over consistency, ability to scale horizontally using map-reduce, and being well-suited for web applications via its RESTful API.

1. Niklas Gustavsson [email_address] www.callistaenterprise.se

2. CouchDB, Slide © Copyright 2008, Callista Enterprise AB Be warned

3. CouchDB, Slide © Copyright 2008, Callista Enterprise AB Won't replace your relational database You (probably) won't be using it any time soon

4. CouchDB, Slide © Copyright 2008, Callista Enterprise AB Forget about relational databases for a while

5. CouchDB, Slide © Copyright 2008, Callista Enterprise AB Open source project started by Damien Katz http://couchdb.org Soon to be an Apache project

6. CouchDB, Slide © Copyright 2008, Callista Enterprise AB How does it work?

7. CouchDB, Slide © Copyright 2008, Callista Enterprise AB Document oriented Documents are JSON {firstName:”Niklas”, lastName: “Gustavsson”} Schema less

8. CouchDB, Slide © Copyright 2008, Callista Enterprise AB Views Pre-computed, indexed table Incrementally updated Written in JavaScript

9. CouchDB, Slide © Copyright 2008, Callista Enterprise AB // sort and retrieve documents by first name function (doc) { map(doc.firstName, doc); } // retrieve squares by size function (sq) { map(sq.width * sq.height, {color: sq.color}); }

10. CouchDB, Slide © Copyright 2008, Callista Enterprise AB 1 2 3 So why should I care?

11. CouchDB, Slide © Copyright 2008, Callista Enterprise AB First reason Sometimes availability trumps consistency 1 2 3

12. CouchDB, Slide © Copyright 2008, Callista Enterprise AB CAP theorem - pick two: Consistency Availability Partitioning

13. CouchDB, Slide © Copyright 2008, Callista Enterprise AB Eventual Consistency http://www.allthingsdistributed.com/2007/12/eventually_consistent.html

14. CouchDB, Slide © Copyright 2008, Callista Enterprise AB NODES – the number of nodes that store a replica WRITES – the number nodes that confirm a commit READS – the number of nodes that are contacted at a read operation WRITES+READS > NODES : strong consistency http://www.allthingsdistributed.com/2007/12/eventually_consistent.html

15. CouchDB, Slide © Copyright 2008, Callista Enterprise AB Synchronous DB replication NODES = 2 WRITES = 2 READS = 1 2 + 1 > 2 -> Strong consistency http://www.allthingsdistributed.com/2007/12/eventually_consistent.html

16. CouchDB, Slide © Copyright 2008, Callista Enterprise AB Asynchronous DB replication NODES = 2 WRITES = 1 READS = 1 1 + 1 > 2 -> Eventual consistency http://www.allthingsdistributed.com/2007/12/eventually_consistent.html

17. CouchDB, Slide © Copyright 2008, Callista Enterprise AB What if NODES is 10 or 100 or 1000? Every increase in WRITES means less chance for a write to succeed

18. CouchDB, Slide © Copyright 2008, Callista Enterprise AB http://www.allthingsdistributed.com/2007/12/eventually_consistent.html http://aws.amazon.com/simpledb http://lucene.apache.org/hadoop/ Read more

19. CouchDB, Slide © Copyright 2008, Callista Enterprise AB Second reason: Moore has changed tactic 1 2 3

20. CouchDB, Slide © Copyright 2008, Callista Enterprise AB CPUs are getting slower but more plenty The Free Lunch is over - http://www.gotw.ca/publications/concurrency-ddj.htm

21. CouchDB, Slide © Copyright 2008, Callista Enterprise AB We need to start parallelizing our tasks Concurrency in Java is really, really hard Share nothing Erlang processes and messaging Map/reduce

22. CouchDB, Slide © Copyright 2008, Callista Enterprise AB Used for computing views in CouchDB map/reduce

23. CouchDB, Slide © Copyright 2008, Callista Enterprise AB http://www.gotw.ca/publications/concurrency-ddj.htm http://erlang.org/ http://www.scala-lang.org/ http://labs.google.com/papers/mapreduce.html Read more

24. CouchDB, Slide © Copyright 2008, Callista Enterprise AB Third reason Web friendly 1 2 3

25. CouchDB, Slide © Copyright 2008, Callista Enterprise AB REST - “HTTP used right”

26. CouchDB, Slide © Copyright 2008, Callista Enterprise AB REST based API Everything is a resource Every resource has a URL Every resource has the same uniform interface Links guides through states Stateless

27. CouchDB, Slide © Copyright 2008, Callista Enterprise AB REST freebies API easily usable from any platform (AJAX, Java, Ruby, COBOL, Powerpoint...)‏ Works with existing infrastructure Caches, proxies, firewalls… Optimistic locking

28. CouchDB, Slide © Copyright 2008, Callista Enterprise AB http://www.ics.uci.edu/~fielding/pubs/dissertation/top.htm http://www.infoq.com/articles/rest-introduction http://www.burtongroup.com/Guest/Aps/RestWorkshop.aspx Read more

29. CouchDB, Slide © Copyright 2008, Callista Enterprise AB I'm getting sleepy, show me the goodies!

30. CouchDB, Slide © Copyright 2008, Callista Enterprise AB Adding a to do var todoText = $("todoinput").value; this.db.save({text: todoText });

31. CouchDB, Slide © Copyright 2008, Callista Enterprise AB Adding a tag if(!todo.tags) { todo.tags = [tag]; } else { todo.tags[todo.tags.length] = tag; } this.db.save(todo);

32. CouchDB, Slide © Copyright 2008, Callista Enterprise AB The magic of save()‏ this.save = function(doc, options) { if (doc._id == undefined) { xhr.open("POST", this.url); } else { xhr.open("PUT", this.url + doc._id); } xhr.send(doc.toJSONString()); … }

33. CouchDB, Slide © Copyright 2008, Callista Enterprise AB Questions? ?

34. CouchDB, Slide © Copyright 2008, Callista Enterprise AB Attributions WHY? - http://www.flickr.com/photos/teflon/128827389/ Deep mud - http://www.flickr.com/photos/hubmedia/133598031/ Banana - http://flickr.com/photos/tim_ellis/154225908/ Forget me not - http://flickr.com/photos/doblonaut/456339900/