relaxing with couchdb
will leinweber
will@bitfission.com
acts_as_conference 2009
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2

this talk: why & how
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what is couchdb?
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document database
no schema
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erlang
concurrent
scalable
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built for the web
restful
json
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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\"
}
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multi version concurrency control
no locking
locking mvcc
write reads
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add only
never in a bad state
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incremental replication
eventual consistency
winning documents
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couchdb only apps
javascript + html
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multiple databases
for a single app
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integrate with full text search
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file attachment
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views
(not queries)
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stored as design documents
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view server
javascript (spidermonkey)
ruby and python too
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map
reduce (optional)
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goes through each document
very slow
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map step
emits keys value pairs
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persisted index
keeps track of changes
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keep your views fresh
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http benefits
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cacheable
load balancers
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easy interface
understand and implement
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getting started
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install couch from svn head
get erlang, spidermonkey, icu
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gem install jchris-couchrest
lightweight api wrapper
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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\"}
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$ curl http://localhost:5984/books/07cb6232593b61dd022d1c05b1c7deac
{\"_id\":\"07cb6232593b61dd022d1c05b1c7deac\",\"_rev\":\"2351730874\",
\"title\":\"recipes\"}
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doc[\"title\"] = \"cook book\"
doc.save # => true
db.get response[\"id\"] # => {\"title\"=>\"cook book\",
\"_id\"=>\"07cb623...\", \"_rev\"=>\"3767210759\"}
doc.destroy # => true
db.get response[\"id\"] # => RestClient::ResourceNotFound
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simple view
function(doc) {
if (doc.type == \"book\") {
emit(null, doc);
}
db.view(\"books/all\")
}
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view with keys
function(doc) {
emit(doc.type, doc);
}
db.view(\"books/all\" )['rows'].size # => 10
db.view(\"all/by_type\" )['rows'].size # => 30
db.view(\"all/by_type\",
:key => \"book\")['rows'].size # => 10
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map reduce
// map // reduce
function(doc) { function(keys,values) {
emit(doc.type, doc); 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}]}
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versioning
{
\"title\": \"Slinkies!\",
\"version\": 4,
\"master_id\": \"3de0c...\",
\"_id\": \"af322...\",
\"chapters\": [...]
}
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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]);
}
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view collation
{ \"_id\": \"def345\",
{ \"_id\": \"abc012\",
\"_rev\": \"2387\",
\"_rev\": \"2387\",
\"type\": \"comment\",
\"type\": \"post\",
\"data\": \"...\" }
\"data\": \"...\" }
{ \"_id\": \"r2d2c3\",
\"_rev\": \"2653\",
\"type\": \"comment\",
\"data\": \"...\" }
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view collation
function(doc) {
if (doc.type == \"post\") {
emit([doc._id, 0], doc);
} else if (doc.type == \"comment\") {
emit([doc.post, 1], doc);
}
}
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CouchRest::Model
being removed from couchrest
class Book < CouchRest::Model
key_accessor :title, :text, :author
cast :author, :as => \"User\"
timestamps!
end
# config/environment.rb
CouchRest::Model.default_database =
CouchRest.database!(\"appname-#{ENV['RAILS_ENV']}\")
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others
langalex-couch_potato
active couch
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downsides
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moving target
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arbitrary queries are slow
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lack of supporting tools
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loss of intuition
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what you should do next
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thanks!
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