CouchDB on Rails - RailsWayCon 2010

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 2

Scalarium EC2 Cluster Management  Auto-conﬁg  Self-Healing  Auto-Scaling  One-click-deployment www.scalarium.com 3

Database Requirements High Availability Easy Replication Clustering Robustness Short Recovery Time 4

CouchDB Build for the Web Scales Replication built-in Embracing ofﬂine Flexible schema – document DB 6

”CouchDB is built of the Web“ Jacob Kaplan-Moss 7

Web Technologies HTTP the access protocol JavaScript the query language JSON the storage format 8

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 } } 9

No Tables or Namespaces 12

No Tables or Namespaces 13

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 } } 14

Interacting with CouchDB JSON HTTP Client PUT /dbname/ID 15

Interacting with CouchDB GET /dbname/ID HTTP Client JSON 16

Interacting with CouchDB DELETE /dbname/ID HTTP Client 17

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){ .... }” } } } 19

Design Document { Document ID "id": "_design/hats”, – "_rev": "431212AB4”, preﬁxed by “_design/” "language": "javascript”, "views": { "all": { "map": "function(doc){ .... }”, "reduce": "function(doc){ .... }” }, "by_manufacturer": { "map": "function(doc){ .... }”, "reduce": "function(doc){ .... }” } } } 20

Design Document { "id": "_design/hats”, "_rev": "431212AB4”, "language": "javascript”, "views": { "all": { Hash of Views "map": "function(doc){ .... }”, "reduce": "function(doc){ .... }” }, "by_manufacturer": { "map": "function(doc){ .... }”, "reduce": "function(doc){ .... }” } } } 21

Design Document { "id": "_design/hats”, "_rev": "431212AB4”, "language": "javascript”, "views": { "all": { Hash of Views "map": "function(doc){ .... }”, Every view has map & "reduce": "function(doc){ .... }” reduce function }, "by_manufacturer": { "map": "function(doc){ .... }”, "reduce": "function(doc){ .... }” } } } 22

Map function(doc) { if (doc.headware) { for (var hat in doc.headware) { emit(hat, 1); } } } 23

Map Passed every document in the DB function(doc) { if (doc.headware) { for (var hat in doc.headware) { emit(hat, 1); } } } 24

Map function(doc) { if (doc.headware) { Inspects for (var hat in doc.headware) { & Decides emit(hat, 1); } } } 25

Map function(doc) { if (doc.headware) { for (var hat in doc.headware) { emit(hat, 1); } } Emits result } for index 26

Reduce function(keys, values, rereduce) { return sum(values); } 27

Reduce Passed map result (or partial reduce result) function(keys, values, rereduce) { return sum(values); } 28

Reduce function(keys, values, rereduce) { return sum(values); } Aggregates (count, sum, average, …) 29

Example Map Result Map functions are similar to SQL indices 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 30

Query a view 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}, ]} 31

Query a view GET /dbname/_design/hats/_view/all? include_docs=true HTTP Client 32

View Query Filter by  key=ABC123  startkey=123 & endkey=9  limit=100  descending=true  group=true  reduce=true  Include_docs=true 33

SQL vs. JavaScript Vs. 34

SQL vs. JavaScript ActiveRecord Vs. SimplyStored 35

SimplyStored Convenience Layer for CouchDB  Models & Associations  Validations  Callbacks BSD-licensed on  Dynamic ﬁnder http://github.com/peritor/simply_stored  S3 attachments On top of CouchPotato, CouchRest & RestClient  Paranoid delete  ActiveModel compliant 36

Setup Install Load in environment.rb Conﬁgure 37

Setup 38

RockingChair In-memory CouchDB  Just a big Hash  Understands all SimplyStored generated views  Speeds up tests  Tests can run in parallel  Nice for debugging BSD-licensed on http://github.com/jweiss/rocking_chair 41

Database Requirements High Availability Easy Replication Clustering Robustness Short Recovery Time 42

Replication B-Tree XXXXX Photo by Mathias Meyer 43

B-Tree Append only Concurrency (MVCC) Crash resistant Hot backups Compaction 44

Replication 45

CouchDB Replication POST /_replicate POST /_replicate Eventually consistent & conﬂict resolution 46

Load Balancing Replication HTTP Client HTTP Load Balancer 47

Caching HTTP Client HTTP Cache Varnish Apache … 48

Multi-Master 49

Sharding/Partitioning with CouchDB Lounge HTTP Client CouchDB Lounge 50

Sharding with CouchDB Lounge HTTP Client CouchDB Lounge 51

Various CouchApps Validations Filtered replication Changes feed Futon Geo Fulltext-Search with embedded Lucene Experimental Ruby-View-Server 52

Q&A Peritor GmbH Blücherstr. 22, Hof III Aufgang 6 10961 Berlin Tel.: +49 (0)30 69 20 09 84 0 Fax: +49 (0)30 69 20 09 84 9 Internet: www.peritor.com E-Mail: info@peritor.com © Peritor GmbH - Alle Rechte vorbehalten

CouchDB on Rails - RailsWayCon 2010

by Jonathan Weiss

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