Meet Couch DB

Esti Álvarez @esti
Conferencia Rails 2010
viernes 5 de noviembre de 2010

Relational DatabasesDocumental Databases
Schema-free Document
Oriented Database

Key Features
• Completely dynamic schema
• Key-value store in JSON format with B-
Tree indexing
• Append-only (all or nothing)
• Concurrent reads and writes
• Very reliable (Erlang)

Replication
• Bidirectional replication with built in
conﬂict resolution
• Ofﬂine by default
• Incremental replication

Database interaction
• Data is stored and returned in JSON
format
• Queried via HTTP RESTful API
• Index building language: Javascript

Database interaction
• Data is stored and returned in JSON
format
• Queried via HTTP RESTful API
• Index building language: Javascript
“Django may be built for theWeb, but CouchDB is built of the Web. I’ve never
seen software that so completely embraces the philosophies behind HTTP.“
Creator of Django

When should I use
CouchDB?
• Concurrent Distributed systems
• Systems where data consistency is
important
• Ofﬂine by default

Futon. http://localhost:5984

Learn by example

JSON data storage
{
"name": "Homer",
"last_names": ["Simpson", "Duff"],
"phone_numbers": {
"mobile": "555-666-777",
"work": "666-777-555"
},
"interests": ["beer", "donuts", "couches"]
}

Schema-less
{
"_id": "debd7e7385464f4874dd2a38043f7825",
"_rev": "3-839e43865b653a1ed73c3d21cc17c5dd",
"name": "Homer",
"phone_numbers": {
"mobile": "555-666-777",
"work": "666-777-555",
"bar": "777-666-555"
},
}

JSON data storage
{
"_id": "debd7e7385464f4874dd2a38043f7825",
"_rev": "3-839e43865b653a1ed73c3d21cc17c5dd",
"name": "Homer",
"phone_numbers": {
"mobile": "555-666-777",
"work": "666-777-555"
},
}

HTTP RESTful API
$ curl http://localhost:5984/ypages
HTTP/1.1 404 Object Not Found
{"error":"not_found","reason":"no_db_file"}

Creating the Database
$ curl -X PUT http://localhost:5984/ypages
HTTP/1.1 201 Created
{"ok":true}

Creating a Document
$curl -v -X PUT http://localhost:5984/ypages/homer -d
'{"name": "Homer",
"phone_numbers": { "mobile": "555-666-777",
"work": "666-777-555"},
"interests": ["beer", "donuts", "couches"]}'
Etag: "1-4a9c28dc2e4227cac13872c89a7875d8"
{"ok":true,"id":"homer","rev":"1-4a9c..."}

Getting a Document
$ curl -X GET http://localhost:5984/ypages/homer
HTTP/1.1 200 OK
Etag: "1-4a9c28dc2e4227cac13872c89a7875d8"
{"_id":"homer","_rev":"1-4a9c...","name":"Homer"...}

Updating a Document
$ curl -v -X PUT http://localhost:5984/ypages/homer -d
'{"_rev": "1-4a9c...",
"name": "Marge",
...}'
Etag: "2-ca3a39967947f974ac021d9f1bdafd1a"
{"ok":true,"id":"homer","rev":"2-ca3a39..."}

Querying the database
• Views: the way to arrange data to answer
our questions
• Method to build views:
Incremental MapReduce using Javascript

Find by name
function(doc) {
if (doc.name) {
emit(doc.name, null);
}
}

Find by name
$ curl '/ypages/_design/app/_view/by_name'
{"total_rows":4,"offset":0,
"rows":[
{"key":"Bart","value":null},
{"key":"Homer","value":null},
{"key":"Lisa","value":null},
{"key":"Marge","value":null}
]}

Find by name
$curl '.../by_name?key="Homer"&include_docs=true'
"rows":[
{"id":"homer",
"key":"Homer",
"value":1,
"doc": {"_id":"debd", "_rev":"3-839", "name":"Homer",
"last_names":["Simpson","Duff"],
"phone_numbers":{"mobile":"555-666-777",
"work":"666-777-555"},
"interests":["beer","donuts","couches"]
}
}
]
}

Find by phone type
Map:
function (doc) {
var type;
if (doc.name && doc.phone_numbers) {
for (type in doc.phone_numbers) {
emit(type, 1);
}
}
}

Count by phone type
Reduce:
function (keys, values, rereduce) {
return sum(values);
}

Count by phone type
$ curl '/ypages/_design/app/_view/by_phone'
{"rows":[{"key":null,"value":9}]}
(reduced by default)

Find by phone type
$ curl '.../by_phone?group=true'
{"rows":[
{"key":"home","value":1},
{"key":"mobile","value":4},
{"key":"work","value":4}
]}

Find by phone type
$ curl '.../by_type?key="work"&reduce=false'
{"total_rows":9,"offset":5,"rows":[
{"key":"work","value":1,"id":"..."},
{"key":"work","value":1,"id":"..."},
{"key":"work","value":1,"id":"..."},
{"key":"work","value":1,"id":"..."}
]}

Many more options
• startkey, endkey, order, limit...
• View’s keys can be anything you like.
Ej. birthdate:
"rows":[
{"key":[2000, 10, 10], "value":"Bart"},
{"key":[1998, 07, 13], "value":"Lisa"},
{"key":[1950, 05, 10], "value":"Homer"},
{"key":[1950, 02, 12], "value":"Marge"}
]}

CouchRest
• A RESTful CouchDB client based on
Heroku's RestClient and Couch.js
• http://github.com/couchrest/couchrest

CouchRest
• dbr=CouchRest.database("http://localhost:5984/ypages")
• record = dbr.get("homer")
=> {"name"=>"Homer", "_rev"=>"3-b87d", "_id"=>"homer"}
• record['name'] = "Moo"
=> "Moo"
• record.save
=> true

Couch Potato
• http://github.com/langalex/couch_potato
• ActiveRecord-like syntax

Couch Potato
class Contact
include CouchPotato::Persistence
property :name
property :last_names
property :phone_numbers
validates_presence_of :name
view :all, :key => :name
view :by_phone, :map => "function(doc) {
var phone_type;
if (doc.name && doc.phone_numbers) {
for (phone_type in doc.phone_numbers) {
emit(phone_type, 1);
}
}
}"

Couch Potato
contacts = CouchPotato.database.view Contact.by_phone
:key => “work”, :include_docs => true
=> [#<Contact _id: "8f4aa”...>, ...]
contacts.each do |contact|
contact.name = “Dr. #{contact.name}”
CouchPotato.database.save_document contact
end

Couch Potato
• Validations
• Callbacks
• Test suite
• ...

Simply Stored
• http://github.com/peritor/simply_stored
• Built on top of Couch Potato
• Associations: has_many, belongs_to
• Sintactic sugar: ﬁnd_by_name

CouchRest Model
• http://github.com/couchrest/couchrest_model
• For Rails 3

Where?
• Ubuntu CouchDesktop (Ubuntu 9.10)
• BBC: fault tolerant, scalable, multi-data
center key-value store.
• 32 nodes in two datacenters.
• A terabyte of data/day
• ~ 5 billion of reqs/year. 150 million reqs/day

Our use case
Tracking the activity on a website during a
live-broadcasted twitter-interview.

Video streaming server logs
(Flash media server)
{
"_id": "ffb297816c756289188ca61dc66d61c7",
"_rev": "1-b78bc6ddfbb1f27259c333694d16ba6a",
"type": "streaming",
"datetime": "2010-03-26 18:15:56",
"x-event": "pause",
"c-client-id": "872845283",
...
}
http://www.irekia.euskadi.net

Web server logs (Apache)
{
"_id": "fde06b5ecd70736e0deb6a22effff25a",
"_rev": "1-f496524ccba837b529426e0ad2177524",
"type": "web",
"datetime": "2010-10-29 08:32:01",
"path": "es/web_tv/agentes-sociales-economicos-suscriben-pacto-social-vivienda",
"user-agent": "Mozilla/4.0 ...",
...
}

Questions made by citizens via Twitter
{
"_id": "219d1d871ad0b9a31b5f10302c8ac03e",
"_rev": "1-a4466ffd843164f0f538532aca7d10c6",
"datetime": "2010-10-26 18:24:37",
"text": "#patxilopez Yo queria preguntar sobre un tema de
actualidad q se esta hablando mucho en la calle: Cuando
tendremos Bob Esponja en Euskera?",
"type": "tweet"
...
}

I want more!
• Get it! http://couchdb.apache.org/
• The Deﬁnitive Guide:
http://guide.couchdb.org/
• Case studies:
http://www.couchone.com/case-studies

Questions?
Sparktography - http://ﬂickr.com/photos/sparktography/65005867/

Meet Couch DB

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