nosqldbs

What's NoSQL

“No SQL”?
“Not Only SQL”?
Non Relational?
Schema-less?

CAP Theorem

From Wikipedia, the free encyclopedia

It is impossible for a distributed data store to simultaneously provide more than two out of the following three guarantees

Consistency	Availability	Partition Tolerance
Every read receives the most recent write or an error	Every request receives a (non-error) response – without guarantee that it contains the most recent write	The system continues to operate despite an arbitrary number of messages being dropped (or delayed) by the network between nodes

Since network partition is usually given in a distributed system, it's pretty much:

Consistency vs. Availability

ACID vs BASE

ACID Consistency Model

Atomic, Consistent, Isolated, Durable
Favors ‘C’ in CAP

BASE Consistency Model

Basically Available Eventually Consistent
Favors ‘A’ in CAP

DB Types

KeyValue DB

CRUD operations for a Key, Value
Examples : Redis, Riak

Document DB

JSON/BSON Documents
Examples: MongoDB, CouchDB

Column Store DB

Data stored with rowkey and column families
Examples: Hbase, Cassandra

Graph DB

Store Entities and Relationships
Examples: Neo4j, Infinite Graph

Key Value DB (Redis)

DataStructure Server (Sets, SortedSets, BitMaps, HyperLogLogs, Pub-Sub)
Serialized Execution of Commands
In-Memory with Periodic Backup or Append Only File (AoF) Persistence

Key Value DB (Riak)

Riak Ring Buffer Based on Amazon’s Dynamo paper http://docs.basho.com/riak/kv/2.2.3/learn/dynamo/

N=Number of replicas

Eventual Consistency

R/W = Read/Write Quorom
R=1 Sloppy quorum, Faster reads, but possibly dirty. Same for W
Increase R, W values for stronger consistency and partition tolerance
Controlled at bucket level
Masterless Architecture
Data Structures
Tables ~= Buckets

Document DB (Mongo)

JSON/Binary JSON (BSON) documents
Collections ~= Tables
Indexing
Queries return cursor

Graph DB (Neo4j)

Nodes and Relationships
Cypher Language
Indexes for Starting Points

Column Store DB (HBase)

Column-Oriented based on Google’s BigTable
Built over HDFS (Hadoop Distributed File Ssytem)
BigData

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