An introduction to CouchDB and how to leverage it from Ruby/Rails presented by Jonathan Weiss at RailsWayCon 2010 in Berlin.

1. CouchDB on Rails
An Introduction
Jonathan Weiss
31.05.2010

2. Who am I?
Working for Peritor in Berlin, Germany
Written, maintain, or involved in
 Webistrano
 Capistrano
 SimplyStored
 Happening
 The great fire of London
http://github.com/jweiss
@jweiss
2

3. Scalarium
EC2 Cluster Management
 Auto-config
 Self-Healing
 Auto-Scaling
 One-click-deployment
www.scalarium.com
3

4. Database Requirements
High Availability
Easy Replication
Clustering
Robustness
Short Recovery Time
4

5. 5

6. CouchDB
Build for the Web
Scales
Replication built-in
Embracing offline
Flexible schema – document DB
6

7. ”CouchDB is built of the Web“
Jacob Kaplan-Moss
7

8. Web Technologies
HTTP
the access protocol
JavaScript
the query language
JSON
the storage format
8

9. JSON Document
{
"_id": "BCCD12CBB",
"_rev": "1-AB764C",
"type": "person",
"name": "Darth Vader",
"age": 63,
"headware": ["Helmet", "Sombrero"],
"dark_side": true,
"weapons": {
"right_arm": "light_saber",
"left_arm": null
}
}
9

10. JSON Document
{
"_id": "BCCD12CBB",
"_rev": "1-AB764C",
"type": "person",
"name": "Darth Vader",
"age": 63,
"headware": ["Helmet", "Sombrero"],
"dark_side": true,
"weapons": {
"right_arm": "light_saber",
"left_arm": null
}
}
10

11. JSON Document
{
"_id": "BCCD12CBB",
"_rev": "1-AB764C",
"type": "person",
"name": "Darth Vader",
"age": 63,
"headware": ["Helmet", "Sombrero"],
"dark_side": true,
"weapons": {
"right_arm": "light_saber",
"left_arm": null
}
}
11

12. No Tables or Namespaces
12

13. No Tables or Namespaces
13

14. Manual Namespacing
{
"_id": "BCCD12CBB",
"_rev": "1-AB764C",
"type": "person",
"name": "Darth Vader",
"age": 63,
"headware": ["Helmet", "Sombrero"],
"dark_side": true,
"weapons": {
"right_arm": "light_saber",
"left_arm": null
}
}
14

15. Interacting with CouchDB
JSON
HTTP Client
PUT /dbname/ID
15

16. Interacting with CouchDB
GET /dbname/ID
HTTP Client
JSON
16

17. Interacting with CouchDB
DELETE /dbname/ID
HTTP Client
17

18. Views
18

19. Design Document
{
"id": "_design/hats”,
"_rev": "431212AB4”,
"language": "javascript”,
"views": {
"all": {
"map": "function(doc){ .... }”,
"reduce": "function(doc){ .... }”
},
"by_manufacturer": {
"map": "function(doc){ .... }”,
"reduce": "function(doc){ .... }”
}
}
} 19

20. Design Document
{ Document ID
"id": "_design/hats”, –
"_rev": "431212AB4”, prefixed by “_design/”
"language": "javascript”,
"views": {
"all": {
"map": "function(doc){ .... }”,
"reduce": "function(doc){ .... }”
},
"by_manufacturer": {
"map": "function(doc){ .... }”,
"reduce": "function(doc){ .... }”
}
}
} 20

21. Design Document
{
"id": "_design/hats”,
"_rev": "431212AB4”,
"language": "javascript”,
"views": {
"all": { Hash of Views
"map": "function(doc){ .... }”,
"reduce": "function(doc){ .... }”
},
"by_manufacturer": {
"map": "function(doc){ .... }”,
"reduce": "function(doc){ .... }”
}
}
} 21

22. Design Document
{
"id": "_design/hats”,
"_rev": "431212AB4”,
"language": "javascript”,
"views": {
"all": { Hash of Views
"map": "function(doc){ .... }”, Every view has map &
"reduce": "function(doc){ .... }” reduce function
},
"by_manufacturer": {
"map": "function(doc){ .... }”,
"reduce": "function(doc){ .... }”
}
}
} 22

23. Map
function(doc) {
if (doc.headware) {
for (var hat in doc.headware) {
emit(hat, 1);
}
}
}
23

24. Map
Passed every
document in the DB
function(doc) {
if (doc.headware) {
for (var hat in doc.headware) {
emit(hat, 1);
}
}
}
24

25. Map
function(doc) {
if (doc.headware) {
Inspects
for (var hat in doc.headware) { & Decides
emit(hat, 1);
}
}
}
25

26. Map
function(doc) {
if (doc.headware) {
for (var hat in doc.headware) {
emit(hat, 1);
}
} Emits result
} for index
26

27. Reduce
function(keys, values, rereduce) {
return sum(values);
}
27

28. Reduce
Passed map result
(or partial reduce result)
function(keys, values, rereduce) {
return sum(values);
}
28

29. Reduce
function(keys, values, rereduce) {
return sum(values);
}
Aggregates
(count, sum, average, …)
29

30. Example Map Result
Map functions are similar to SQL indices
ID KEY VALUE
51ABFA211 Cap 1
ABC123456 Cappy 1
BCCD12CBB Helmet 1
BCCD12CBB Sombrero 1
Sorted by the key
Key can also be an array
Value can be complex JSON
30

31. Query a view
GET /dbname/_design/hats/_view/all
HTTP Client
{"total_rows":348,"offset":0,"rows”:[
{"id":"A","key":"A","value":1},
{"id":"B","key":"B","value":1},
]}
31

32. Query a view
GET /dbname/_design/hats/_view/all?
include_docs=true
HTTP Client
32

33. View Query
Filter by
 key=ABC123
 startkey=123 & endkey=9
 limit=100
 descending=true
 group=true
 reduce=true
 Include_docs=true
33

34. SQL vs. JavaScript
Vs.
34

35. SQL vs. JavaScript
ActiveRecord
Vs.
SimplyStored
35

36. SimplyStored
Convenience Layer for CouchDB
 Models & Associations
 Validations
 Callbacks BSD-licensed on
 Dynamic finder http://github.com/peritor/simply_stored
 S3 attachments On top of CouchPotato, CouchRest & RestClient
 Paranoid delete
 ActiveModel compliant
36

37. Setup
Install
Load in environment.rb
Configure
37

38. Setup
38

39. 39

40. 40

41. RockingChair
In-memory CouchDB
 Just a big Hash
 Understands all SimplyStored generated views
 Speeds up tests
 Tests can run in parallel
 Nice for debugging
BSD-licensed on
http://github.com/jweiss/rocking_chair
41

42. Database Requirements
High Availability
Easy Replication
Clustering
Robustness
Short Recovery Time
42

43. Replication
B-Tree
XXXXX
Photo by Mathias Meyer
43

44. B-Tree
Append only
Concurrency (MVCC)
Crash resistant
Hot backups
Compaction
44

45. Replication
45

46. CouchDB Replication
POST /_replicate
POST /_replicate
Eventually consistent & conflict resolution
46

47. Load Balancing
Replication
HTTP Client HTTP Load
Balancer
47

48. Caching
HTTP Client HTTP Cache
Varnish
Apache
…
48

49. Multi-Master
49

50. Sharding/Partitioning with
CouchDB Lounge
HTTP Client CouchDB
Lounge
50

51. Sharding with CouchDB Lounge
HTTP Client CouchDB
Lounge
51

52. Various
CouchApps
Validations
Filtered replication
Changes feed
Futon
Geo
Fulltext-Search with embedded Lucene
Experimental Ruby-View-Server
52

53. Q&A
Peritor GmbH
Blücherstr. 22, Hof III Aufgang 6
10961 Berlin
Tel.: +49 (0)30 69 20 09 84 0
Fax: +49 (0)30 69 20 09 84 9
Internet: www.peritor.com
E-Mail: info@peritor.com
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