Relaxing With CouchDB

relaxing with couchdb will leinweber will@bitfission.com acts_as_conference 2009 1

this talk: why & how 3

what is couchdb? 4

document database no schema 5

erlang concurrent scalable 6

built for the web restful json 7

json { quot;titlequot;: quot;A Brief History of Slinkiesquot;, quot;chaptersquot;: [ { quot;titlequot;: quot;Sorta like a springquot;, quot;textquot;: quot;Round and metal...quot; }, { quot;titlequot;: quot;Stairsquot;, quot;textquot;: quot;They can go down, but not upquot; }], quot;_idquot;: quot;4b859...quot;, quot;_revquot;: quot;3280991488quot; } 8

multi version concurrency control no locking locking mvcc write reads 9

add only never in a bad state 10

incremental replication eventual consistency winning documents 11

couchdb only apps javascript + 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 server javascript (spidermonkey) ruby and python too 18

map reduce (optional) 19

goes through each document very slow 20

map step emits keys value pairs 21

persisted index keeps track of changes 22

keep your views fresh 23

http benefits 24

cacheable load balancers 25

easy interface understand and implement 26

getting started 27

install couch from svn head get erlang, spidermonkey, icu 28

gem install jchris-couchrest lightweight api wrapper 29

db = CouchRest.database!(quot;http://localhost:5984/booksquot;) response = db.save(:title => quot;recipesquot;) # => {quot;revquot;=>quot;2351730874quot;, quot;idquot;=>quot;07cb62...quot;, quot;okquot;=>true} doc = db.get response[quot;idquot;] # => {quot;titlequot;=>quot;recipesquot;, quot;_idquot;=>quot;07cb62...quot;, quot;_revquot;=>quot;2351730874quot;} 30

$ curl http://localhost:5984/books/07cb6232593b61dd022d1c05b1c7deac {quot;_idquot;:quot;07cb6232593b61dd022d1c05b1c7deacquot;,quot;_revquot;:quot;2351730874quot;, quot;titlequot;:quot;recipesquot;} 31

doc[quot;titlequot;] = quot;cook bookquot; doc.save # => true db.get response[quot;idquot;] # => {quot;titlequot;=>quot;cook bookquot;, quot;_idquot;=>quot;07cb623...quot;, quot;_revquot;=>quot;3767210759quot;} doc.destroy # => true db.get response[quot;idquot;] # => RestClient::ResourceNotFound 32

simple view function(doc) { if (doc.type == quot;bookquot;) { emit(null, doc); } db.view(quot;books/allquot;) } 34

view with keys function(doc) { emit(doc.type, doc); } db.view(quot;books/allquot; )['rows'].size # => 10 db.view(quot;all/by_typequot; )['rows'].size # => 30 db.view(quot;all/by_typequot;, :key => quot;bookquot;)['rows'].size # => 10 35

map reduce // map // reduce function(doc) { function(keys,values) { emit(doc.type, doc); return(values.length); } } db.view(quot;count/by_typequot;) # => {quot;rowsquot;=> {quot;valuequot;=>3, quot;keyquot;=>nil}]} db.view(quot;count/by_typequot;, :group => true) # => {quot;rowsquot;=>[{quot;valuequot;=>10, quot;keyquot;=>quot;articlequot;}, {quot;valuequot;=>10, quot;keyquot;=>quot;bookquot;}, {quot;valuequot;=>10, quot;keyquot;=>quot;userquot;}]} db.view(quot;count/by_typequot;, :key => quot;bookquot;) # => {quot;rowsquot;=>[{quot;valuequot;=>10, quot;keyquot;=>nil}]} 36

versioning { quot;titlequot;: quot;Slinkies!quot;, quot;versionquot;: 4, quot;master_idquot;: quot;3de0c...quot;, quot;_idquot;: quot;af322...quot;, quot;chaptersquot;: [...] } 37

versioning // map // reduce function(doc) { function(keys, values) { emit( doc.master_id, var max = 0; doc ); } for(i in values) { if( values[i].version > values[max].version ) { max = i; } } return(values[max]); } 38

view collation { quot;_idquot;: quot;def345quot;, { quot;_idquot;: quot;abc012quot;, quot;_revquot;: quot;2387quot;, quot;_revquot;: quot;2387quot;, quot;typequot;: quot;commentquot;, quot;typequot;: quot;postquot;, quot;dataquot;: quot;...quot; } quot;dataquot;: quot;...quot; } { quot;_idquot;: quot;r2d2c3quot;, quot;_revquot;: quot;2653quot;, quot;typequot;: quot;commentquot;, quot;dataquot;: quot;...quot; } 39

view collation function(doc) { if (doc.type == quot;postquot;) { emit([doc._id, 0], doc); } else if (doc.type == quot;commentquot;) { emit([doc.post, 1], doc); } } 40

CouchRest::Model being removed from couchrest class Book < CouchRest::Model key_accessor :title, :text, :author cast :author, :as => quot;Userquot; timestamps! end # config/environment.rb CouchRest::Model.default_database = CouchRest.database!(quot;appname-#{ENV['RAILS_ENV']}quot;) 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

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Relaxing With CouchDB

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