NoSQL - An introduction to CouchDB

CouchDB A Database for the Web

Jonathan Weiss

Who am I?

Working for Peritor in Berlin, Germany

Written, maintain, or involved in

Webistrano

Capistrano

SimplyStored

Happening

The great fire of London

http://github.com/jweiss

@jweiss

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Scalarium

Amazon EC2 Cluster Management

Auto-config

Self-Healing

Auto-Scaling

One-click-deployment

www.scalarium.com

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Database Requirements

High Availability

Easy Replication

Clustering

Robustness

Short Recovery Time

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CouchDB

Build for the Web

Scales

Replication built-in

Embracing offline

Flexible schema – document DB

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”CouchDB is built of the Web“ Jacob Kaplan-Moss

Web Technologies

HTTP the access protocol

JavaScript the query language

JSON the storage format

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JSON Document

{ "_id": "BCCD12CBB", "_rev": "1-AB764C", "type": "person", "name": "Darth Vader", "age": 63, "headware": ["Helmet", "Sombrero"], "dark_side": true, "weapons": { "right_arm": "light_saber", "left_arm": null } }

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JSON Document


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JSON Document


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No Tables or Namespaces

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No Tables or Namespaces

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Manual Namespacing


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Interacting with CouchDB

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PUT /dbname/ID

JSON

HTTP Client


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JSON

GET /dbname/ID

HTTP Client


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DELETE /dbname/ID HTTP Client

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Views

Design Document { "id": "_design/hats”, "_rev": "431212AB4”, "language": "javascript”, "views": { "all": { "map": "function(doc){ .... }”, "reduce": "function(doc){ .... }” }, "by_manufacturer": { "map": "function(doc){ .... }”, "reduce": "function(doc){ .... }” } } }

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Document ID –

prefixed by “_design/”


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Hash of Views


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Hash of Views Every view has map &

reduce function

Map

function(doc) { if (doc.headware) { for (var hat in doc.headware) { emit(hat, 1); } } }

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Map


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Passed every document in the DB

Map


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Inspects & Decides

Map


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Emits result for index

Reduce

function(keys, values, rereduce) { return sum(values); }

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Reduce


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Passed map result (or partial reduce result)

Reduce


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Aggregates (count, sum, average, …)

Example Map Result

Map functions are similar to SQL indices

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ID KEY VALUE

51ABFA211 Cap 1

ABC123456 Cappy 1

BCCD12CBB Helmet 1

BCCD12CBB Sombrero 1

Sorted by the key

Key can also be an array

Value can be complex JSON and/or reference to other document

Query a view

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GET /dbname/_design/hats/_view/all

HTTP Client

{"total_rows":348,"offset":0,"rows”:[ {"id":"A","key":"A","value":1}, {"id":"B","key":"B","value":1}, ]}

Query a view

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GET /dbname/_design/hats/_view/all?include_docs=true

HTTP Client

View Query

Filter by

key=ABC123

startkey=123 & endkey=9

limit=100

descending=true

group=true

reduce=true

Include_docs=true

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SQL vs. JavaScript

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Vs.

Using Couch from PHP

Several options available

PHPillow: http://arbitracker.org/phpillow.html (LGPL 3)

PHP Object_Freezer: https://github.com/sebastianbergmann/php-object-freezer/tree (BSD)

PHP On Couch: http://github.com/dready92/PHP-on-Couch/tree/master (GPLv2 or v3)

PHP CouchDB Extension: http://www.topdog.za.net/php_couchdb_extension (PHP License 3.0)

Sag for CouchDB: http://www.saggingcouch.com/ (Apache License 2.0)

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SimplyStored

CouchDB convenience Layer for Ruby

Models & Associations

Validations

Callbacks

Dynamic finder

S3 attachments

Paranoid delete

ActiveModel compliant

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BSD-licensed on http://github.com/peritor/simply_stored

On top of CouchPotato, CouchRest & RestClient

Many more

Or just build your own using HTTP!

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Database Requirements

High Availability

Easy Replication

Clustering

Robustness

Short Recovery Time

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Replication

XXXXX

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B-Tree

Photo by Mathias Meyer

B-Tree

Append only

Concurrency (MVCC)

Crash resistant

Hot backups

Compaction

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Replication

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CouchDB Replication

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POST /_replicate

POST /_replicate

Eventually consistent & conflict resolution

Load Balancing

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HTTP Client HTTP Load Balancer

Replication

Caching

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HTTP Client HTTP Cache Varnish Apache …

Multi-Master

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BigCouch

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Clustered CouchDB:

Many CouchDBs appear as one

Modeled after Amazon Dynamo

Scalability like Cassandra or Riak

github.com/cloudant/bigcouch

BigCouch

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Q – No. of partitions

N – No. of replicas

R – Read quorum

W – Write quorum

Various

CouchApps

Validations

Filtered replication

Changes feed

List functions

Futon

Geo

Fulltext-Search with embedded Lucene

Different experimental View-Server 52

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NoSQL - An introduction to CouchDB

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