The document provides an overview of CouchDB, including: - It is a schema-free, document-oriented database that uses HTTP and JSON. - It supports features like multi-master replication, append-only documents, and map/reduce views. - The document demonstrates how to perform basic CRUD operations in CouchDB using HTTP requests. - Map/reduce functions are used to index and aggregate document data to enable efficient querying.

1. Relax!
Sebastian Cohnen
@tisba / tisba.de
Mittwoch, 16. November 11

2. About Me
• Freier Entwickler
❤ Ruby/Rails & node.js
❤ Performance & Scalability Engineering
❤ Distributed Load Testing
❤ CouchDB, Redis & Riak
und ebenfalls interessiert an Erlang, AMQP, ...
Mittwoch, 16. November 11

3. Users of Couchdb
BBC
meebo
UbuntuOne
...
adcloud
Mittwoch, 16. November 11

4. CouchDB: Basics
Schema-frei
Dokumenten-orientiert
Key/Value-Speicher
fehlertolerant & robust
Mittwoch, 16. November 11

5. Key Features
HTTP + JSON
Multi-Master Replikation
AP aus CAP
Append-only
inkrementelle, materialisierte Views (map/reduce)
Mittwoch, 16. November 11

6. HTTP & JSON
Mittwoch, 16. November 11

7. Admin Interface
Mittwoch, 16. November 11

8. Create A Database
$ curl -w%{http_code} -X PUT http://127.0.0.1:5984/test_db ↵
{"ok":true}
201
$ $ curl -w%{http_code} -X GET http://127.0.0.1:5984/test_db
↵
{"db_name":"test_db","doc_count":0,"doc_del_count":0,
"update_seq":1,"purge_seq":0, "compact_running":false,
"disk_size":16473, "instance_start_time":
"1253091887127542","disk_format_version":4}
200
* $ alias curl='curl -w%{http_code} -X'
Mittwoch, 16. November 11

9. create A Document
$ curl POST -d '{"hello":"world"}' http://127.0.0.1:5984/
test_db ↵
{"ok":true,"id":"67729d5013cf3f8858eb29cb17e5a723","rev":"1-1
5f65339921e497348be384867bb940f"}
201
read
$ curl GET http://127.0.0.1:5984/test_db/
67729d5013cf3f8858eb29cb17e5a723 ↵
{"_id":"67729d5013cf3f8858eb29cb17e5a723","_rev":"1-15f653399
21e497348be384867bb940f","hello":"world"}
200
Mittwoch, 16. November 11

10. update
$ curl PUT -d
'{"_rev":"1-15f65339921e497348be384867bb940f",
"hello":"world","message":"about to show CRUD in couch"}'
http://127.0.0.1:5984/test_db/
2f41f56816191b94ecbd127151faa242 ↵
{"ok":true,"id":"2f41f56816191b94ecbd127151faa242","rev":"2-2
873c60120aa6dbe2204cd2c1a0e8722"}
201
$ curl GET http://127.0.0.1:5984/test_db/
2f41f56816191b94ecbd127151faa242 ↵
{"_id":"2f41f56816191b94ecbd127151faa242","_rev":"2-2873c6012
0aa6dbe2204cd2c1a0e8722","hello":"world","message":"about to
show CRUD in couch"}
200
Mittwoch, 16. November 11

11. delete
$ curl DELETE http://127.0.0.1:5984/test_db/
67729d5013cf3f8858eb29cb17e5a723?
rev=1-15f65339921e497348be384867bb940f ↵
{"ok":true,"id":"67729d5013cf3f8858eb29cb17e5a723","rev":"2-2
d715caed35974bb33de24d1d6c95779"}
200
$ curl GET http://127.0.0.1:5984/test_db/
67729d5013cf3f8858eb29cb17e5a723 ↵
{"error":"not_found","reason":"deleted"}
404
Mittwoch, 16. November 11

12. CouchApps
Dokumente können Attachments haben
CouchDB als HTTP Server
HTML+CSS+JS ausgeliefert von CouchDB greift via
HTTP auf CouchDB als Datenbank zu
Beispiel: Kabul War Diary
http://upondata.com:5984/afgwar/_design/afgwardiary/
index.html
Mittwoch, 16. November 11

13. Replikation
Mittwoch, 16. November 11

14. Replikation
Replikation läuft via HTTP
asynchron
inkrementell (online-offline)
automatische Konfliktlösung
Multi-Version Concurrency Control (MVCC)
Multi-Master als default
filterbar
Mittwoch, 16. November 11

15. Map/Reduce Views
Mittwoch, 16. November 11

16. Accessing Data
direkter Zugriff via http://server/DATABASE/DOC-ID
materialisierte Views
bestehen aus einer map-Phase
und einer optionalen reduce-Phase
show & list: (Dokument) Transformationen
filters, externals, ...
Mittwoch, 16. November 11

17. Views
sortiert, inkrementell, effizienter Zugriff via B-Trees
build-in Viewserver:
JavaScript (Spidermonkey)
Erlang
3rd Party Viewserver in Ruby, Python, Java, Perl, ...
Mittwoch, 16. November 11

18. map/reduce
map: Eine Funktion, welche key/value Paare in einen
Index schreibt
Beispiel Tag-Cloud:
1 function(doc) {
2 if (doc.tags) {
3 for(var idx in doc.tags) {
4 emit(doc.tags[idx], 1);
5 }
6 }
7 }
Mittwoch, 16. November 11

19. map example
{“body”:”[...]”, “tags”:[“erlang”, “couchdb”]}
{“body”:”[...]”, “tags”:[“couchdb”, “talk”, “rails”]}
map-function(doc)
{“key”:“couchdb”, “value”:1}
{“key”:“couchdb”, “value”:1}
{“key”:“erlang”, “value”:1}
{“key”:“rails”, “value”:1}
{“key”:“talk”, “value”:1}
* indices are automatically sorted
Mittwoch, 16. November 11

20. map/reduce
reduce wird verwendet, um das Ergebnis der map-
Phase zu verarbeiten
1 function(keys, values, rereduce) {
2 return sum(values);
3 }
Mittwoch, 16. November 11

21. reduce example
{“key”:“erlang”: “value”:1}
{“key”:“couchdb”: “value”:1}
{“key”:“couchdb”: “value”:1}
{“key”:“talk”: “value”:1}
{“key”:“rails”: “value”:1}
reduce function(...)
{"key":"erlang","value":1}
{"key":"couchdb","value":2}
{"key":"talk","value":1}
{"key":"rails","value":1}
Mittwoch, 16. November 11

22. CouchDB: Pros
HTTP (Proxy, Caches, Loadbalancer, ...)
HTTP (CouchDB als Webserver, 2-tier Apps!)
Replikation
Views sind sortiert; effizienter Zugriff auf Ranges
Mittwoch, 16. November 11

23. Cons
Append-only erfordert Compaction
Append-only & MVCC/Konfliktlösung führen zu
Probleme bei Update-heavy Anwendungen
keine verteilte Datenbank (sharding, clustering)
Mittwoch, 16. November 11

24. Get it!
http://couchdb.apache.org/downloads.html
brew install couchdb / apt-get install couchdb / ...
freies Hosting: www.iriscouch.com
BigCouch (cloudant.com / https://github.com/cloudant/bigcouch)
dynamo-style CouchDB Cluster
Couchbase (www.couchbase.com)
Membase+CouchDB
Mittwoch, 16. November 11

25. Thanks! Q & A?
?
Sebastian Cohnen
@tisba
Mittwoch, 16. November 11

26. Understanding
reduce
1 function(keys, values, rereduce) {}
a b c d | e f g h | i j k l | m n
1 2 1 3 | 1 2 3 1 | 2 3 3 1 | 1 8
7 7 | 9 9
14 18
32
function( [[“a”,id1],[“b”,id2],[“c”,id3],[“d”,id4]],
[1, 2, 1, 3],
false) {...}
function(null, [ 7, 7], true) {...}
function(null, [ 9, 9], true) {...}
function(null, [14,18], true) {...}
Mittwoch, 16. November 11