What are the main features of couchdb?

Document-oriented storage: CouchDB stores data in the form of JSON documents, which makes it easy to work with and flexible enough to handle a wide range of data types. Replication: CouchDB has a built-in replication feature that allows data to be synchronized across multiple instances of the database, which makes it easy to create distributed applications.

 Features:

• It has an HTTP-based REST API.
• It has a simple structure of HTTP resources and methods.
• Data is stored in the flexible document-based structure
• It provides easy-to-use replication.

CouchDB is one of what many are calling NoSQL solutions. Specifically, CouchDB is a document-oriented database and within each document fields are stored as key-value maps. Fields can be either a simple key/value pair, list, or map.

Each document that is stored in the database is given a document-level unique identifier (_id) as well as a revision (_rev) number for each change that is made and saved to the database.

NoSQL databases represent a shift away from traditional relational databases and can offer many benefits (and their own challenges) as well. CouchDB offers us these features:

• Easy replication of a database across multiple server instances
• Fast indexing and retrieval
• REST-like interface for document insertion, updates, retrieval and deletion
• JSON-based document format (easily translatable across different languages)
• Multiple libraries for your language of choice (show some of the popular language choices)
• Subscribable data updates on the _changes feed

* JSON Documents : CouchDB stores data in JSON document.

* RESTful Interface : CouchDB does all tasks like replication, data insertion, etc. via HTTP.

* N-Master Replication : CouchDB facilitates you to make use of an unlimited amount of 'masters,' making for some very interesting replication topologies.

* Built for Offline : CouchDB can replicate to devices (like Android phones) that can go offline and handle data sync for you when the device is back online.

* Replication Filters : CouchDB facilitates you to filter precisely the data you wish to replicate to different nodes.

* ACID semantics : The CouchDB file layout follows all the features of ACID properties. Once the data is entered into the disc, it will not be overwritten. Document updates (add, edit, delete) follow Atomicity, i.e., they will be saved completely or not saved at all. The database will not have any partially saved or edited documents. Almost all of these update are serialized, and any number of clients can read a document without waiting and without being interrupted.

* Document storage : CouchDB is a NoSQL database which follows document storage. Documents are the primary unit of data where each field is uniquely named and contains values of various data types such as text, number, Boolean, lists, etc. Documents don't have a set limit to text size or element count.

* Eventually consistency : CouchDB guarantees to provide availability and partition tolerance.

Authentication and Session Support: CouchDB facilitates you to keep authentication open via a session cookie like a web application.

* Security : CouchDB also provides database-level security. The permissions per database are separated into readers and admin. Readers can both read and write to the database.

* Validation : You can validate the inserted data into the database by combining with authentication to ensure the creator of the document is the one who is logged in.

Map/Reduce List and Show: The main reason behind the popularity of MongoDB and CouchDB is map/reduce system.