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MongoDB Overview

I have started to work with Mongodb so think start blogging about MongoDB. I will try to write very simple language which will give you great understanding on MongoDB concept to create and deploy a highly scalable and performance oriented database.
MongoDB is an open-source document database is written in c++, and leading NoSQL database.
MongoDB is a cross-platform, document oriented database that provides, high performance, high availability, and easy scalability. MongoDB works on concept of collection and document.
MONGODB OVERVIEW
Database: Database physically contains the collections. Each database gets its own set of files on the file system. A single MongoDB server usually has multiple databases.
Collection: This is equivalent to RDBMS table; basically collection is group of MongoDB Documents. A collection exists within a single database. Collections do not insist on a schema. Documents within a collection can have different fields. Naturally, all documents in a collection are of similar or related purpose.
Document: Document is a set of key-value pairs. Documents have dynamic schema. Dynamic schema means that documents in the same collection do not need to have the same set of fields or structure, and common fields in a collection's documents may hold different types of data.


RDBMS
MongoDB
Database
Database
Table
Collection
Tuple/Row
Document
column
Field
Table Join
Embedded Documents
Primary Key
Primary Key (Default key _id provided by mongodb itself)
Database Server and Client
Mysqld/Oracle
mongod
mysql/sqlplus
mongo

Sample document
Below given example shows the document structure of a blog site which is simply a comma separated key value pair

{
   _id: ObjectId(4gf66u875)
   title: 'MongoDB Overview',
   description: 'MongoDB is no sql database',
   by: 'codefari',
   url: 'http://www.codefari.com',
   tags: ['mongodb', 'database', 'NoSQL'],
   likes: 100,
   comments: [  
      {
         user:'user1',
         message: 'My first comment',
         dateCreated: new Date(2015,1,20,2,43),
         like: 0
      },
      {
         user:'user2',
         message: 'My second comments',
         dateCreated: new Date(2015,1,25,7,34),
         like: 5
      }
   ]
}
_id is a 12 bytes hexadecimal number which assures the uniqueness of every document. You can provide _id while inserting the document. If you didn't provide then MongoDB provide a unique id for every document. These 12 bytes first 4 bytes for the current timestamp, next 3 bytes for machine id, next 2 bytes for process id of MongoDB server and remaining 3 bytes are simple incremental value.

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