CouchDBCS 510 – Fall 2011

Andy PhenixKhanh Nguyen

Elakkiya PandianSharmadha Moorthy

Anitha Suryanarayan

Why use CouchDB● Store complex data structures - JSON● Store variable data structures - no schema● De-normalized / self contained● Add attachments to documents● Scalable and fault tolerant

● Better fit for certain problem domains○ Messaging○ CMS

Data Model■ Self Contained Documents - JSON

■ View engine - JavaScript

■ Consistency: Atomic, conflicts resolved by clients.

■ Querying and Indexing : based on Map-Reduce

■ Lock Free Design and eventual consistency

Data Model

Data Model

■ RESTful HTTP /JSON API accessible from many programming libraries and tools

■ API Types ○ Server level○ Database level○ Document level

API's

unsigned long addr = 0xff00ff20;unsigned int block = addr & 0x1f;unsigned int set = (addr & 0x7e0) >> 5;unsigned int tag = (addr & 0xfffff800) >> 11;

Code Sample DescriptionGET /somedatabase/some_doc_id?rev=946B7D1C HTTP/1.0 To retrieve a document.

GET /somedatabase/some_doc_id?rev=946B7D1C HTTP/1.0 See Document Revisions for additional notes on revisions.

HEAD /somedatabase/some_doc_id HTTP/1.0 Returns basic information about the document, including its current revision.

PUT /somedatabase/some_doc_id HTTP/1.0Content-Length: 245Content-Type: application/json{"Subject":"I like Plankton","Author":"Rusty","PostedDate":"2006-08-15T17:30:12-04:00","Tags":["plankton", "baseball", "decisions"],"Body":"I decided today that I don't like baseball. I like plankton."}

To create/update a named document.

POST /somedatabase/ HTTP/1.0Content-Length: 245Content-Type: application/json{"Subject":"I like Plankton","Author":"Rusty","PostedDate":"2006-08-15T17:30:12-04:00","Tags":["plankton", "baseball", "decisions"],"Body":"I decided today that I don't like baseball. I like plankton."}

Create a new document with a server generated DocID

DELETE /somedatabase/some_doc?rev=1582603387 HTTP/1.0 To delete a document.

COPY /somedatabase/some_doc HTTP/1.1Destination: some_other_doc Copy documents

Data Model■ JSON

○ Example of a JSON document:

{

"_id":"discussion_tables",

"_rev":"D1C946B7",

"FullHours":[1,2,3,4,5,6,7,8,9,10],

"Activities": [

{"Name":"Football", "Duration":2, "DurationUnit":"Hours"},

{"Name":"Breakfast", "Duration":40, "DurationUnit":"Minutes", "Attendees":["Jan", "Damien", "Laura", "Gwendolyn"]}

]

}

Query Support● Functional Query Language

● Views ○ Map-reduce functions ○ indexed with specific key fields○ Stored in a B-Tree structure

● Automatic Query Optimization

Query Support

Query SupportTypes of Queries

● Range Queries■ Very efficient; Efficiency O(log N)■ B-trees for document and index storage

● Point, Navigation and Arbitrary Queries■ Supported if appropriate indexes are built.■ Search without indexed key are not supported in

CouchDB.

Query Support● Sample query request from a view:

Point based : /blog/_design/docs/_view/by_date?key="2009/01/30 18:04:11”

Range based : /blog/_design/docs/_view/by_date?startkey="2010/01/01 00:00:00"&endkey="2010/02/00 00:00:00“

Indexes● B-Tree Structure

● Types : ○ Document index○ View index

● Automatic management by Couch DB View server

Example map Function

Key (indexed)– (item,price)

Value - store

Example map Function

Key (indexed)– (item,price)

Value - store

Storage● Append only file structure

● B-tree with two header copies

● “Crash-only” design - protects data integrity

● Flexible - can run on smart phone to a cluster

Transactions & Concurrency Control

● Only within single document

● ACID semantics

● MVCC - “optimistic locking”

● Lock-free design

● Writes serialized when data is actually written to the disk.

Transactions and Concurrency Control

● eventual consistency by incremental replication

● 'shared nothing' cluster

● no single point of contention

Scalability● Horizontal scaling via replication

● Map-reduce queries

● Partitioning via add-ons○ Lounge○ Pillow○ BigCouch

Replication● Asynchronous● Flexible Schemes● User-initiated via HTTP request

○ Specifies Source -> Target

● Client Application Resolves Conflicts● Limited Support for Automation

Replication● Replication Scenarios

○ Client/Server

○ Peer-to-Peer

○ Master/Slave

○ Multi-master

Platform● POSIX systems - GNU/Linux and OS X

○ Windows is not officially supported

● Cloud Infrastructure○ Apache○ Cloudant○ Iris couch○ Amazon Machine Images

Platform/Deployment● Language binding

○ C,C#,ColdFusion,Erlang,ExtJS,Haskell○ Java,Javascript,LISP,LotusScript,Lua,NodeJS,Objective-C○ Ocaml,Perl,PHP,Python,Ruby,Smalltalk,Vmware

● Communication Protocols○ RESTful HTTP methods - POST, GET, PUT ,DELETE○ cURL ○ Encoding - JSON

Platform/Deployment● Lounge

● CouchRest ○ CouchRest-ExtendedDocument

● A CouchApp

● Couch potato

● CouchFoo

References

http://wiki.apache.org/couchdb/FrontPagehttp://en.wikipedia.org/wiki/Couchdbhttp://sitr.us/2009/09/13/couchdb-notes.htmlhttp://wiki.apache.org/couchdb/Frequently_asked_questionshttp://www.oscon.com/oscon2009/public/schedule/detail/8076http://guide.couchdb.org/editions/1/enhttp://www.couchbase.com/customers/case-studies

CouchDB in Production

● BBC

● MEEBO.COM

● CERN

● US Dept of Education and Defense

.

Thank You!