CouchDB has several features that help it stand out from the other databases in this rapidly growing field. Incremental map/reduce, peer to peer replication, mobile device synchronization, a realtime update feed, and the ability to host an application in the database itself (also known as a Couchapp) are just a few. See how companies such as the BBC, Radical Dynamic, Signal, and Incandescent Software are using CouchDB to solve their real world challenges.

1. Real World
John Wood
Windy City DB 2011
@johnpwood

2. About Me

3. • Software Developer at Signal
• Coding for about 15 years
• Working with CouchDB for 2.5 years (in
production for about 2 years)
• Enjoy tinkering with data storage solutions

4. CouchDB Overview

5. Document Database
{
“_id” : “2d7f015226a05b6940984bbe39004fde”,
“_rev” : “2-477f6ab2dec6df185de1a078d270d8”,
“first_name” : “John”,
“last_name” : “Wood”,
“interests” : [“hacking”, “fishing”, “reading”],
“offspring” : [
{ “name” : “Dylan”, “age” : 6 },
{ “name” : “Chloe”, “age” : 3 }
]
}

6. Strong Focus on
Replication

7. RESTful API
# Create
POST http://localhost:5984/employees
# Read
GET http://localhost:5984/employees/1
# Update
PUT http://localhost:5984/employees/1
# Delete
DELETE http://localhost:5984/employees/1

8. Queried and Indexed
with MapReduce
function(doc) {
if (doc.first_name == “John”)
emit(doc._id, 1);
}
function(keys, values, rereduce) {
return sum(values);
}

9. Ultra Durable

10. Erlang OTP

11. Views

12. MapReduce
// Map
function(doc) {
emit(doc._id, 1);
}
// Reduce
function(keys, values, rereduce) {
return sum(values);
}

13. MapReduce
// Map
function(doc) {
if (doc.dependents) {
for (i in doc.dependents) {
emit(doc._id, doc.dependents[i]);
}
}
}
// Reduce
_count

14. MapReduce
function(keys, values, rereduce) {
function sum(type_counts, totals, status) {
if (type_counts[status]) { // OK or ERR
if (!totals[status]) {
totals[status] = new Object();
}
var status_totals = totals[status];
var status_type_counts = type_counts[status];
for (key in status_type_counts) { // MO, MT, CM, etc.
var count = status_type_counts[key];
if (!status_totals[key]) {
status_totals[key] = count;
} else {
status_totals[key] += count;
}
}
}
}
var totals = new Object();
// values should be something like
// {"OK":{"MO":1234,"MT":1000,"CM":20},"ERR":{"MO":1,"MT": 1}}
for (i = 0; i < values.length; i++) {
var message_count = values[i];
sum(message_count, totals, 'OK');
}
return totals;
}

15. Design Documents
{
"_id": "_design/stats",
"views": {
"total_employees": {
"map": "function(doc) { emit(doc._id, 1); }",
"reduce": "function(keys, values, rereduce) { return
sum(values); }"
},
"by_lastname": {
"map": "function(doc) { emit(doc.last_name, null); }"
},
"dependents": {
"map": "function(doc) { if (doc.dependents) { for (i in
doc.dependents) { emit(doc._id, doc.dependents[i]); } } }",
"reduce": "_count"
}
}
}

16. {
"_id": "1",
"first_name": "Robert", {
"last_name": "Johnson", "_id": "4",
"date_hired": "2010/01/10", "first_name": "Bob",
"dependents": [ { { "last_name": "Smith",
{ "first_name": "Margie", "last_name": "Johnson" }, "_id": "2", "_id": "3", "salary": 80000,
{ "first_name": "Charlie", "last_name": "Johnson" }, "first_name": "Jim", "first_name": "Sally", "date_hired": "2010/03/11",
{ "first_name": "Sophie", "last_name": "Johnson" } "last_name": "Jones", "last_name": "Stevenson", "dependents": [
], "date_hired": "2010/02/11", "date_hired": "2010/04/23", { "first_name": "Susan", "last_name": "Smith" }
"salary": 250000 "salary": 150000 "salary": 100000 ]
} } } }
MapReduce
{"total_rows":4,"offset":0,"rows":[
{"id":"1","key":"1","value":{"first_name":"Margie","last_name":"Johnson"}},
{"id":"1","key":"1","value":{"first_name":"Charlie","last_name":"Johnson"}},
{"id":"1","key":"1","value":{"first_name":"Sophie","last_name":"Johnson"}},
{"id":"4","key":"4","value":{"first_name":"Susan","last_name":"Smith"}}
]}

17. {
"_id": "1",
"first_name": "Robert", {
"last_name": "Johnson", "_id": "4",
"date_hired": "2010/01/10", "first_name": "Bob",
"dependents": [ { { "last_name": "Smith",
{ "first_name": "Margie", "last_name": "Johnson" }, "_id": "2", "_id": "3", "salary": 80000,
{ "first_name": "Charlie", "last_name": "Johnson" }, "first_name": "Jim", "first_name": "Sally", "date_hired": "2010/03/11",
{ "first_name": "Sophie", "last_name": "Johnson" } "last_name": "Jones", "last_name": "Stevenson", "dependents": [
], "date_hired": "2010/02/11", "date_hired": "2010/04/23", { "first_name": "Susan", "last_name": "Smith" }
"salary": 250000 "salary": 150000 "salary": 100000 ]
} } } }
MapReduce
{"rows":[
{"key":null,"value":4}
]}

18. {
"_id": "1",
"first_name": "Robert", {
"last_name": "Johnson", "_id": "4",
"date_hired": "2010/01/10", "first_name": "Bob",
"dependents": [ { { "last_name": "Smith",
{ "first_name": "Margie", "last_name": "Johnson" }, "_id": "2", "_id": "3", "salary": 80000,
{ "first_name": "Charlie", "last_name": "Johnson" }, "first_name": "Jim", "first_name": "Sally", "date_hired": "2010/03/11",
{ "first_name": "Sophie", "last_name": "Johnson" } "last_name": "Jones", "last_name": "Stevenson", "dependents": [
], "date_hired": "2010/02/11", "date_hired": "2010/04/23", { "first_name": "Susan", "last_name": "Smith" }
"salary": 250000 "salary": 150000 "salary": 100000 ]
} } } }
MapReduce
{"rows":[
{"key":"1","value":3},
{"key":"4","value":1}
]}

19. View Structure
http://guide.couchdb.org/editions/1/en/views.html

20. View Structure
?key="ch"
http://guide.couchdb.org/editions/1/en/views.html

21. Real World Example

22. The Problem
• Reports that utilized data in some large tables (30M+
rows) were taking a very long to create
• Increasing query execution times
• Occasional page timeouts
• Limited resources for super powered hardware or the
leading relational database product
• Database migrations on these large tables were taking an
increasingly long time to run

23. The Solution
• Using CouchDB as an archive database
• Migrated old data in tables to CouchDB, dramatically
reducing the tables sizes, speeding up queries that were
still hitting those tables
• Re-wrote SQL queries as views to fetch data from the
archive database, dramatically reducing the amount of
time needed to fetch the old data
• Views updated nightly with the new set of archived data

24. Replication

25. POST /_replicate
{"source":"database",
"target":"http://example.org/database"}

26. Unidirectional

27. Bidirectional

28. Continuous

29. Filtered
function(doc, req) {
if (doc.type && doc.type == "foo") {
return true;
} else {
return false;
}
}

30. Filtered
function(doc, req) {
if (doc.type && doc.type == req.query.doc_type) {
return true;
} else {
return false;
}
}

31. Named

32. Conflicts

33. "_conflicts":
["2-7c971bb974251ae8541b8fe045964219"]

34. Finding Conflicts
function(doc) {
if (doc._conflicts) {
emit(doc._conflicts, null);
}
}
{"total_rows":1,"offset":0,"rows":[
{"id":"foo","key":
["2-7c971bb974251ae8541b8fe045964219"],"value":null}
]}
http://guide.couchdb.org/draft/conflicts.html

35. Resolving Conflicts
# Step 1
PUT /db/document {... merged data ...}
# Step 2
DELETE /db/document?
rev=2-7c971bb974251ae8541b8fe045964219

36. Real World Example
http://www.couchbase.com/case-studies/bbc

37. The Problem
• Need to make sure site was always up and available, even
in the face of a data center catastrophe
• Needed a solution that could easily replicate data
between two or more data centers
• Needed the solution to store data in a safe and reliable
way
http://www.couchbase.com/case-studies/bbc

38. The Solution
• Using CouchDB to create a multi-master, multi-data
center failover configuration
• 32 nodes in the cluster
• 16 nodes in each of their two data centers
• 8 primary nodes, 8 backup nodes
• Terabyte of data
• 150 - 170 million requests per day
http://www.couchbase.com/case-studies/bbc

39. My Guess at BBC’s Replication Setup
App
Load
Balancer
P1 P2 P3 P4 P5 P6 P7 P8 P1 P2 P3 P4 P5 P6 P7 P8
B1 B2 B3 B4 B5 B6 B7 B8 B1 B2 B3 B4 B5 B6 B7 B8

40. Change Notifications

41. {"seq":12,"id":"foo","changes":
[{"rev":"1-23202479633c2b380f79507a776743d5"}]}

42. Polling
GET /db/_changes
{"results":[
{"seq":1,"id":"test","changes":
[{"rev":"1-aaa8e2a031bca334f50b48b6682fb486"}]},
{"seq":2,"id":"test2","changes":
[{"rev":"1-e18422e6a82d0f2157d74b5dcf457997"}]}
],
"last_seq":2}

43. Polling
GET /db/_changes?since=1
{"results":[
{"seq":2,"id":"test2","changes":
[{"rev":"1-e18422e6a82d0f2157d74b5dcf457997"}]}
],
"last_seq":2}

44. Polling
GET /db/_changes?since=1
&include_docs=true
{"results":[
{"seq":2,"id":"test2","changes":
[{"rev":"1-e18422e6a82d0f2157d74b5dcf457997"}],
,"doc":{"_id":"test2", "name":"John", "age":"33",
"_rev":"1-e18422e6a82d0f2157d74b5dcf457997"}}
],
"last_seq":2}

45. Long Polling
GET /db/_changes?feed=longpoll
&since=2

46. Continuous Changes
GET /db/_changes?feed=continuous

47. Filtered Changes
GET /db/_changes?filter=filters/
signal_employees
function(doc, req) {
if (doc.company == “Signal”) {
return true;
} else {
return false;
}
}

48. Filtered Changes
GET /db/_changes?filter=filters/
employees&company=Signal
function(doc, req) {
if (doc.company == req.query.company) {
return true;
} else {
return false;
}
}

49. Real World Example
http://www.couchbase.com/case-studies/skechers

50. Sketchers
• Already using CouchDB to help power
www.sketchers.com
• Utilized the _changes long poll feature to add a “What’s
happening now” widget to the main page
• Updates are processed in real time
• The widget was written in just a few hours, with the
majority of the code handling the display of the data
http://www.couchbase.com/case-studies/skechers

51. Real World Example
http://www.dimagi.com/pulling-data-from-couchdb-to-a-relational-database-made-easy-with-_changes/

52. “Perhaps at the top of the list of ‘things that are annoying in CouchDB’ is
general reporting.”
http://browsertoolkit.com/fault-tolerance.png

53. dimagi
• “Perhaps at the top of the list of ‘things that are annoying
in CouchDB’ is general reporting.”
• CouchDB views are not nearly as flexible as SQL
• Using the _changes feed to mirror changes made in
CouchDB over to a relational database
• The relational database is used more extensive reporting
• “Couch to SQL in 20 lines of code!”
http://www.dimagi.com/pulling-data-from-couchdb-to-a-relational-database-made-easy-with-_changes/

54. Real World Example
couchdb-lucene
https://github.com/rnewson/couchdb-lucene

55. couchdb-lucene
• Provides full text search functionality for data stored in
CouchDB
• Uses the continuous _changes feed to stay notified of the
most recent changes in the database
• Documents are included with change notifications
• Index is updated shortly after document is saved in
CouchDB
https://github.com/rnewson/couchdb-lucene

56. Mobile Device Support

58. Image credit: http://happyclouddesign.blogspot.com/

59. Image credit: http://gmflightlog.blogspot.com

60. Image credit: http://gmflightlog.blogspot.com

61. Image credit: http://happyclouddesign.blogspot.com/

63. Real World Example
http://www.couchbase.com/case-studies/groupcomplete

64. The Problem
• Looking to modernize mobile data collection (surveys, etc)
• People collecting the data (mobile workers) have limited ability to
review or modify data once it is submitted
• Mobile workers work in a void, unable to collaborate with their
team members, and increasing the likelihood of double-entry and
duplicated effort
• Mobile workers don’t have access to aggregated data, as this is
usually done on the back end, where the data is sent
• Access to a laptop or desktop is required to perform certain tasks
http://www.couchbase.com/case-studies/groupcomplete

65. The Solution
• Cluster of CouchDB servers with shared forms, data, and profiles for
mobile devices collecting data
• A native application running on the device collects the data, and
interacts with a local CouchDB server
• Native application can access the data on the remote servers, or
locally via replicated databases served by CouchDB running on the
device
• Since data can be stored locally, access is fast, and unaffected by spotty
network availability
http://www.couchbase.com/case-studies/groupcomplete

66. The Solution
• Mobile workers can easily share form templates and data
• The application manages conflicts, allowing mobile workers to
update, correct, and revise collected data at any time
• Resolved conflicts are distributed to the team via standard
replication, so everybody has the same data
• Rich media (pictures, audio, video) stored as _attachments
http://www.couchbase.com/case-studies/groupcomplete

67. CouchApps

68. HTTP/1.1 200 OK
Server: CouchDB/1.0.2 (Erlang OTP/R14B)
Date: Tue, 07 Jun 2011 12:24:36 GMT
Content-Type: text/plain;charset=utf-8
Content-Length: 40
Cache-Control: must-revalidate
{"couchdb":"Welcome","version":"1.0.2"}

69. !=

74. Open Data

75. https://github.com/benoitc/afgwardiary

76. JSON != HTML

77. Show Functions
function(doc, req) {
return '<h1>' + doc.title + '</h1>';
}
http://guide.couchdb.org/draft/show.html

78. Show Functions
function(doc, req) {
return {
body : "<foo>" + doc.title + "</foo>",
headers : {
"Content-Type" : "application/xml",
"X-My-Own-Header": "foo"
}
}
}
http://guide.couchdb.org/draft/show.html

79. List Functions
function(head, req) {
send('<ul>');
while (row = getRow()) {
send('<li>' + row.value + '</li>');
}
return('</ul>');
}

80. String concatenation to build HTML? Ewww!
How do I get all of my Javascript into CouchDB?
Can I use my existing development tools?
What about images, CSS files, and other resources?

81. The CouchApp Project
• Scripts that allow you to easily deploy your CouchApp from your
file system to CouchDB
• Where the files live on your filesystem determine where they will
be pushed to the database. myapp/views/foobar/map.js will be
pushed to _design/myapp, into a view named foobar, as the map
function.
https://github.com/couchapp/couchapp

82. The CouchApp Project
• Evently - A declarative, CouchDB friendly jQuery library for writing
event based Javascript applications
• jquery.couch.js - Javascript library for communicating with CouchDB
• jquery.pathbinder.js - Framework for triggering events based on
paths in URL hash
• mustache.js - A simple javascript template framework
https://github.com/couchapp/couchapp

83. Templates
<!DOCTYPE html>
<html>
<head>
<title>Example</title>
<link rel=”stylesheet” href=”../../style/
screen.css” type=”text/css”>
</head>
<body>
<h1 id=”post_title”>{{title}}</h1>
<div id=”post_body”>{{body}}</div>
</body>
<script src=”../../script/awesome.js”></script>
</html>

84. Templates
// Show Function
function(doc, req) {
var mustache = require("vendor/couchapp/lib/mustache");
var data = {
title : doc.title,
body : doc.body
};
return mustache.to_html(this.templates.blog_post, data);
}

85. Real World Example
http://www.couchbase.com/case-studies/incandescent

86. The Problem
• Wanted to develop a web based solution for managing a
veterinary clinic (managing patients, procedures, back
office, etc)
• Needed something that could operate in an environment
without an internet connection
• Wanted something flexible enough to scale up to a SaaS
offering
http://www.couchbase.com/case-studies/incandescent

87. The Solution
• The application was built as an installable CouchApp
• Written entirely in HTML and Javascript
• Developed using Backbone.js
• Platform independent, running on all platforms and
browsers (iPad too!)
• iPhone and Android versions in development
http://www.couchbase.com/case-studies/incandescent

88. Resources

89. Resources
CouchDB Project Website
http://couchdb.apache.org
CouchDB: The Definitive Guide
http://guide.couchdb.org
CouchDB Project Wiki
http://wiki.apache.org/couchdb
CouchApps
http://couchapp.org

90. ?

91. Thanks!
john@johnpwood.net
@johnpwood