Apache
CouchDB

Hello
Chris Anderson
jchris@apache.org / @jchris
Apache CouchDB Committer
REST and JavaScript enthusiast
Director, couch.io

I’m here to answer the question: What is CouchDB? (from an app devs perspective - and some
implementor)
How many of you have:
built an application around a key value store?
written map reduce functions?
used Erlang in an application?

Relax
- easy to reason about
- reliable - your data is safe with us.
- honda accord, not a ferrari
- as a debating point among developers

Bandwidth Explosion

“no bars”

http://www.flickr.com/photos/hercwad/2290378571/

Latency Sucks
speed of light
drawback to cloud computing

What is
CouchDB?
- k/v store with map reduce
- http database written in erlang

Local Web
Local Web
Platform
Platform
- on your device, local network, in a browser plugin
- replication: it just works. makes data portable.
- real-time remote backups, ad hoc topologies.

“Ground Computing”
@jhuggins
http://www.flickr.com/photos/mcpig/872293700/
- local to the user, more like desktop web than like Gears
- local http server
- browser apps
- same application on the client and server or the cloud

Offline by Default
http://www.flickr.com/photos/shane-h/280084650
- low latency & reliable
- 2 tier applications

http://apod.nasa.gov/apod/ap050930.html
“Of the Web”
http://jacobian.org/writing/of-the-web/
Let me tell you something: Django may be built for the Web, but CouchDB is built of the Web. I've never seen software that so completely embraces the philosophies behind HTTP. ... this is
what the software of the future looks like. Jacob Kaplan-Moss -- October, 2007
perfect spot - discovered not invented

- lower barrier for contribution
- validate installations
- foster interop (CouchDB as a protocol)

Learning Curve
- doc modeling (mvcc / concurrency)
- etags / Functional style of REST
- eventual consistency

http://www.longnow.org/projects/clock/
http://www.longnow.org/projects/clock/orrery/

Robust
- single file
- append only
- no fixup phase
- minimizes seeks

Robust
- when britain is burning
- Enda Farrell - bbc

{
"_id": "BC4ea69ce1a73aa7d21d23b608d221d
"_rev": "1-967a00dff5e02add41819138abb32
JSON Documents
"type": "person",
"name": "Darth Vader",
"age": 63,
"headware":
["Helmet", "Sombrero"],
"dark_side": true
}
- denormalize
- natural data behavior
- evolve formats with your application
- easier to bootstrap in your mind

{
"_id": "BC4ea69ce1a73aa7d21d23b608d221d
"_rev": "1-967a00dff5e02add41819138abb32
JSON Documents
"type": "person",
"name": "Darth Vader",
"age": 63,
"headware":
["Helmet", "Sombrero"],
"dark_side": true
}
- 2 patterns
- document update
- event log

{
"_id": "BC4ea69ce1a73aa7d21d23b608d221d
"_rev": "2-41819138abb32967a00dff5e02ad
JSON Documents
"type": "person",
"name": "Darth Vader",
"age": 63,
"headware":
["Helmet", "Sombrero"],
"dark_side": “More CoWbell!”
}
- MVCC
- model for concurrency


Map Reduce

http://horicky.blogspot.com/2008/10/couchdb-implementation.html

ful 
http://www.flickr.com/photos/calliope/3573471166

db

http://code.google.com/p/couchdb-lounge/
http://www.flickr.com/photos/aussiegall/658457636

curl -X POST
http://127.0.0.1:5984/_replicate
-d
'{
"source":
"http://couch.example.com:5984/remote-db",
"target":
"local-db"
}'

curl -X POST
http://127.0.0.1:5984/_replicate
-d
'{
"source":
"http://couch.example.com:5984/remote-db",
"target":
"local-db"
}'

periodic, notifier system

“In the fullness of time there is only one CouchDB”

standalone CouchDB applications

Scaling Down

Browser Couch
JavaScript port
Uses HTML5 storage
Replicates with CouchDB
http://hg.toolness.com/browser-couch/

Gives Control to Users
CC-BY-SA http://www.flickr.com/photos/kelleys/492253912/
- want to get kids in trouble for programming too much
claris

Stuart Langridge - Canonical
! !

- good because it's the status quo
- easy to address with URLs
- bad because users are depending on a remote resource for low latency responses
- centralized, so traffic spikes impact all users, who might start refreshing

- local requests are fast
- easier to tune for throughput
- plays to the strengths of mobile connections

- users can run different applications on the same dataset
deployment
Independent
Personal
- dark matter of the information universe

messaging
peer discovery
identity
Can we trust intermediate servers?

“Obvious.”
web architecture

Local Web
Platform

anks!

Resources
@CouchDB
http://couchdb.apache.org/
Dress like a Couch: http://shop.couchdb.com
http://planet.couchdb.org/
https://peepcode.com/products/couchdb-with-rails

@couchdbinaction
http://books.couchdb.org/relax

Robust
JSON
HTTP
Local

Conflict resolution by
example
A B
couch.io

Conflict resolution by
example
A B
❦
couch.io

Conflict resolution by
example
A B
❦
couch.io

Conflict resolution by
example
A B
❦ ❦
couch.io

Conflict resolution by
example
A B
❦ ❦
couch.io

Conflict resolution by
example
A B
❦ ✿
❦
couch.io

Conflict resolution by
example
A B
❦ ✿
❦
couch.io

Conflict resolution by
example
A B
✿
couch.io

Conflict resolution by
example
A B
✿
couch.io

Conflict resolution by
example
A B
✿
couch.io

Conflict resolution by
example
A B
✿
couch.io

CC-by-nd http://www.flic.kr/photos/eifelyeti110/273939759/