relaxing with couchdb

relaxing with couchdbwill leinweber

will@bitfission.com

acts_as_conference 20091

2

this talk: why & how

3

what is couchdb?

4

document databaseno schema

5

erlangconcurrentscalable

6

built for the webrestfuljson

7

json{ "title": "A Brief History of Slinkies", "chapters": [{ "title": "Sorta like a spring", "text": "Round and metal..." },{ "title": "Stairs", "text": "They can go down, but not up" }],

"_id": "4b859...", "_rev": "3280991488" }

8

multi version concurrency controlno locking

locking mvccwrite reads

9

add onlynever in a bad state

10

incremental replicationeventual consistencywinning documents

11

couchdb only appsjavascript + html

12

multiple databases for a single app

13

integrate with full text search

14

file attachment

15

views(not queries)

16

stored as design documents

17

view serverjavascript (spidermonkey)ruby and python too

18

mapreduce (optional)

19

goes through each documentvery slow

20

map stepemits keys value pairs

21

persisted indexkeeps track of changes

22

keep your views fresh

23

http benefits

24

cacheableload balancers

25

easy interfaceunderstand and implement

26

getting started

27

install couch from svn headget erlang, spidermonkey, icu

28

gem install jchris-couchrestlightweight api wrapper

29

db = CouchRest.database!("http://localhost:5984/books")response = db.save(:title => "recipes") # =>

{"rev"=>"2351730874", "id"=>"07cb62...", "ok"=>true}

doc = db.get response["id"] # => {"title"=>"recipes","_id"=>"07cb62...", "_rev"=>"2351730874"}

30

$ curl http://localhost:5984/books/07cb6232593b61dd022d1c05b1c7deac{"_id":"07cb6232593b61dd022d1c05b1c7deac","_rev":"2351730874","title":"recipes"}

31

doc["title"] = "cook book"doc.save # => truedb.get response["id"] # => {"title"=>"cook book",

"_id"=>"07cb623...", "_rev"=>"3767210759"}

doc.destroy # => truedb.get response["id"] # => RestClient::ResourceNotFound

32

33

function(doc) { if (doc.type == "book") { emit(null, doc); }}

simple view

db.view("books/all")

34

function(doc) { emit(doc.type, doc);}

view with keys

db.view("books/all" )['rows'].size # => 10db.view("all/by_type" )['rows'].size # => 30db.view("all/by_type", :key => "book")['rows'].size # => 10

35

// mapfunction(doc) { emit(doc.type, doc);}

map reduce// reducefunction(keys,values) { return(values.length);}

db.view("count/by_type") # => {"rows"=> {"value"=>3, "key"=>nil}]}db.view("count/by_type", :group => true) # =>

{"rows"=>[{"value"=>10, "key"=>"article"}, {"value"=>10, "key"=>"book"}, {"value"=>10, "key"=>"user"}]}

db.view("count/by_type", :key => "book") # =>{"rows"=>[{"value"=>10, "key"=>nil}]}

36

versioning{ "title": "Slinkies!", "version": 4, "master_id": "3de0c...", "_id": "af322...", "chapters": [...]}

37

versioning// mapfunction(doc) { emit( doc.master_id, doc );}

// reducefunction(keys, values) { var max = 0; for(i in values) { if( values[i].version > values[max].version ) { max = i; } } return(values[max]);}

38

view collation{ "_id": "abc012", "_rev": "2387", "type": "post", "data": "..." }

{ "_id": "def345", "_rev": "2387", "type": "comment", "data": "..." }

{ "_id": "r2d2c3", "_rev": "2653", "type": "comment", "data": "..." }

39

view collationfunction(doc) { if (doc.type == "post") { emit([doc._id, 0], doc); } else if (doc.type == "comment") { emit([doc.post, 1], doc); }}

40

CouchRest::Modelbeing removed from couchrest

class Book < CouchRest::Model key_accessor :title, :text, :author cast :author, :as => "User" timestamps!end

# config/environment.rbCouchRest::Model.default_database = CouchRest.database!("appname-#{ENV['RAILS_ENV']}")

41

others langalex-couch_potato active couch

42

downsides

43

moving target

44

arbitrary queries are slow

45

lack of supporting tools

46

loss of intuition

47

what you should do next

48

thanks!

49