NoSQL (Not Only SQL)

NoSQL stores data in distribued machines.

Replication Model:

• Master-slave replication one copy is a master copy, all writes are applied to master copy, read is done through slave nodes, no gaurantee that their values are up-to-date.
• Master-master replication allows reads/writes at any of the replicas.

Sharding

Split a file and distribute into multiple nodes to distribute the load of accessing the file m=by multiple users

Sharding + replication of shards help load balancing and data availablity.

Types of NoSQL Systems

• Documennt-based store data using well-known formats like JSON. E.g. MongoDB
• Key-value systems Use ley-value paris for fast access. E.g. Amazon's DynamoDB, Facebook's Cassandra
• Column-based Partitiona columns into column families, each family stored in its own file. E.g. Google's BigTable
• Gaph-based data represented as graph. E.g. GraphBase

MongoDB

• storing data in binary JSON (BSON) format
• to create a collection of documents

db.createCollection(name, collection_options)

Example:

db.createCollection("posts", {capped:true, size:1310720, max:500})

MongoDB CRUD operations

• Create create a document to be inserted into a collection: db.<collection_name>.insert(<documents>)
• Read find a document in a collection: db.<collection_name>.find(<condtion>)
• Update update a document: db.<collection_name>.update(<documents>)
• Delete remove a document from a collection: db.<collection_name>.remove(<condition>)

MongoDB in action

Download MongoDB at https://www.mongodb.com/lp/download

• Create a directory to store the files

  mkdir <direcory-name>

• Launch the server

  mongodb --dbpath <directory-name>

  • Launch the client

    mongo

Useful commands

• db
• show dbs
• use <db-name>
• show collections

Example

> db.createCollection("employees", {'capped':true, size=10000, mX:50})

> show collections

> db.movies.insert({Name:'Alex', Age:37, City:'Detroit', Department: 'IT'})

> db.movies.insert({Name:'Bob', Age:25, City:'Detroit', Department: 'HR', Marital_status: 'Single'})

> db.movies.insert({Name:'John', Age:32, City:'An Arbor', Department: 'IT'})

Find records

> db.employees.find({City: 'Ann Arbor'})

> db.employees.find({Marital_status: {$exists: true}})

Query logical operators

• $eq and $ne
• $gt and $gte
• $lt and $lte
• $in and $nin
• $or and $and
• $not and $nor
• $exists