CouchDB on Rails - FrozenRails 2010

CouchDB on Rails
An Introduction

FrozenRails
Jonathan Weiss
07.05.2010

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

Scalarium

EC2 Cluster Management
 Auto-conﬁg
 Self-Healing
 Auto-Scaling
 One-click-deployment

www.scalarium.com

3

Database Requirements

High Availability

Easy Replication

Clustering

Robustness

Short Recovery Time

4

CouchDB

Build for the Web

Scales

Replication built-in

Embracing ofﬂine

Flexible schema – document DB

6

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

7

Web Technologies

HTTP
the access protocol

JavaScript
the query language

JSON
the storage format

8

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

JSON Document

{
"_id": "BCCD12CBB",
"_rev": "1-AB764C",
"type": "person",
"age": 63,
"dark_side": true,
"weapons": {
"left_arm": null
}
}
10

JSON Document

{
"_id": "BCCD12CBB",
"_rev": "1-AB764C",
"type": "person",
"age": 63,
"dark_side": true,
"weapons": {
"left_arm": null
}
}
11

No Tables or Namespaces

12

No Tables or Namespaces

13

Manual Namespacing

{
"_id": "BCCD12CBB",
"_rev": "1-AB764C",
"type": "person",
"age": 63,
"dark_side": true,
"weapons": {
"left_arm": null
}
}
14

Interacting with CouchDB

JSON

HTTP Client

PUT /dbname/ID

15


GET /dbname/ID

HTTP Client

JSON

16


DELETE /dbname/ID
HTTP Client

17

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

Design Document
{ Document ID
"id": "_design/hats”, –
"_rev": "431212AB4”, preﬁxed by “_design/”
"views": {
"all": {
},
}
}
} 20

Design Document
{
"_rev": "431212AB4”,
"views": {
"all": { Hash of Views
},
}
}
} 21

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

Map

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

23

Map
Passed every
document in the DB

function(doc) {
if (doc.headware) {
emit(hat, 1);
}
}
}

24

Map

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

25

Map

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

26

Reduce

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

27

Reduce
Passed map result
(or partial reduce result)

return sum(values);
}

28

Reduce

return sum(values);
}

Aggregates
(count, sum, average, …)

29

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

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

Query a view

GET /dbname/_design/hats/_view/all?
include_docs=true

HTTP Client

32

View Query

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

33

SQL vs. JavaScript

Vs.

34

SQL vs. JavaScript

ActiveRecord

Vs.

SimplyStored

35

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

Setup
Install

Load in environment.rb

Conﬁgure

37

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

Database Requirements

High Availability

Easy Replication

Clustering

Robustness

Short Recovery Time

42

Replication
B-Tree
XXXXX

Photo by Mathias Meyer
43

B-Tree

Append only

Concurrency (MVCC)

Crash resistant

Hot backups

Compaction

44

CouchDB Replication

POST /_replicate

POST /_replicate

Eventually consistent & conﬂict resolution

46

Load Balancing

Replication

HTTP Client HTTP Load
Balancer

47

Caching

HTTP Client HTTP Cache
Varnish
Apache
…

48

Sharding/Partitioning with
CouchDB Lounge

HTTP Client CouchDB
Lounge

50

Sharding with CouchDB Lounge

HTTP Client CouchDB
Lounge

51

Various

CouchApps

Validations

Filtered replication

Changes feed

Futon

Geo

Fulltext-Search with embedded Lucene

Experimental Ruby-View-Server

52

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

© Peritor GmbH - Alle Rechte vorbehalten

CouchDB on Rails - FrozenRails 2010

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