couchdb on rails - railswaycon 2010
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CouchDB on Rails An Introduction
Jonathan Weiss 31.05.2010
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
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
{ "_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
{ "_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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No Tables or Namespaces
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No Tables or Namespaces
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Manual Namespacing
{ "_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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Interacting with CouchDB
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PUT /dbname/ID
JSON
HTTP Client
Interacting with CouchDB
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JSON
GET /dbname/ID
HTTP Client
Interacting with CouchDB
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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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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/”
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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Hash of 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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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
function(doc) { if (doc.headware) { for (var hat in doc.headware) { emit(hat, 1); } } }
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Passed every document in the DB
Map
function(doc) { if (doc.headware) { for (var hat in doc.headware) { emit(hat, 1); } } }
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Inspects & Decides
Map
function(doc) { if (doc.headware) { for (var hat in doc.headware) { emit(hat, 1); } } }
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Emits result for index
Reduce
function(keys, values, rereduce) { return sum(values); }
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Reduce
function(keys, values, rereduce) { return sum(values); }
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Passed map result (or partial reduce result)
Reduce
function(keys, values, rereduce) { return sum(values); }
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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
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.
SQL vs. JavaScript
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Vs.
ActiveRecord
SimplyStored
SimplyStored
Convenience Layer for CouchDB
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
Setup
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Install
Load in environment.rb
Configure
Setup
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RockingChair
In-memory CouchDB
Just a big Hash
Understands all SimplyStored generated views
Speeds up tests
Tests can run in parallel
Nice for debugging
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BSD-licensed on http://github.com/jweiss/rocking_chair
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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Sharding/Partitioning with CouchDB Lounge
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HTTP Client CouchDB Lounge
Sharding with CouchDB Lounge
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HTTP Client CouchDB Lounge
Various
CouchApps
Validations
Filtered replication
Changes feed
Futon
Geo
Fulltext-Search with embedded Lucene
Experimental Ruby-View-Server
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