The document talks about the overview behind the need and drive for NoSQL databases. It also mentions about some of the most popular NoSQL databases in the market.

1. September, 2014
NoSQL – A Quick Tour

2. Objectives What is NoSQL How is data growing ? Challenges What’s the solution ? NoSQL Features and Types Eventual Consistency High-level Overview of some popular No-SQL DB NoSQL – Not mandatory Popular Jargons Useful Links

3. What is NoSQL Abbreviation of “Not an SQL”, any data source which doesn’t come under SQL category A new way to store and retrieve data (specially sparse and unstructured) in modern day high-volume real-time web traffic, batch processing, and analytics Not an alternative for RDBMS but a parallel concept A “Shared Nothing” architecture as opposed to “Shared Architecture” in RDBMS (Philosophy of Shared Nothing (NA) architecture - A shared nothing architecture (SN) is a distributed computing architecture in which each node is independent and self-sufficient, and there is no single point of contention across the system. More specifically, none of the nodes share memory or disk storage.). The term was first coined by Michael Stonebraker at University of California at Berkeley in his 1986 paper “The Case for Shared Nothing.” Can be tagged with technologies which doesn’t use SQL and relational mapping of data Promotes huge storage of data and efficient retrieval, supports normal CRUD operations Not a stringent follower of ACID due to its inherent nature Works with “Big Data” for supporting high volume processing of data Comes with varied flavor of products often coined due to research at social networking giants like Twitter, Facebook, LinkedIn, Google, Yahoo etc. Data can be stored in four basic databases like key/value pair, column-family data, document, and graph

4. What is NoSQL Continued.. Mostly these stores or databases don’t expect pre-defined schemas or normalization and consistency
Primary purpose of NoSQL is to have fast and efficient storing and processing of constantly growing data without the constraint of relation database and provide the scalable architecture to support future growth of data without compromising the performance First generation and second generation of NoSQL
Mantra of NoSQL : “Getting an answer quickly is more important than getting a correct answer” If you can’t split it, you can’t scale it
—Randy Shoup, Distinguished Architect, eBay

5. How is data growing ?

6. How is data growing ? Continued..
There are two concepts Big User and Big Data along with Cloud Computing Big User – Number of users accessing web is growing rapidly accessing several kind of data such Personal information, social data like tweets, likes, blogs, click streams, comments, follows, or geo location data, log files, system generated data, user generated data, sensor-generated data etc. The growing number of users can’t be predicted specially the advancement of mobile space Big Data – Source of data has increased tremendously but the actual data increased exponentially. Data is not in-terms of gigabyte but in more higher number (tera/penta/exa/zetta/yotta bytes) Cloud Computing – More and more Data is stored in the cloud and access to data should be fast
The number of concurrent users skyrocketed as applications increasingly became accessible via the web (and later on mobile devices)
 The amount of data collected and processed soared as it became easier and increasingly valuable to capture all kinds of data
 The amount of unstructured or semi-structured data exploded and its use became integral to the value and richness of applications

7. Challenges
Shared
Application Server Layer to Traditional RDBMS
Add CPU
Add RAM
Vertical
Shared Disk
Oh No! I am loaded
Application Server Layer to NoSQL DB
Commodity Server
Commodity Server
Commodity Server
Commodity Server
Commodity Server

8. Challenges Continued..
Need to scale out (i.e. sharding) and without compromising latency and performance (keeping low latency and high throughout)
Need to avoid scale up with costly and complex high-end servers
Should be easily scaled out with low cost commodity servers without any application downtime
Data is not only structured but majority of the social networking data is unstructured. So, there is a need to support schema less data structures
There are many cases where transaction is not of prime concern and costly and heavy writes are not needed
Should support easy and quick replication as well as failover

9. What’s the solution ?
Real time and batch processing for analytical and operational data by second generation of NoSQL like Couchbase
The picture depict a scenario where both batch processing as well as real-time data is being handled by a combination of Hadoop and Couchbase.

10. NoSQL Features and Types
Early adopter: Google’s Bigtable is used for throughput sensitive batch processing to latency based online queries. Used in Google Earth, Finance, Orkut, Analytics etc. This is based on the concept of column family data store.
There are mainly 3 types of NoSQL databases as mentioned below.
Document Database
MongoDB and Couchbase (An amalgamated version of CouchDB and Membase)
Couchebase started as Apache incubator project and then continued by Couchbase Inc
Implemented in Erlang and C, and Javascript execution environment
Used by Apple, BBC, and many others.

11. NoSQL Features and Types Continued..
Key/Value pair and Eventual Consistency datastore Redis, Membase, Voldemort, and Cassandra Cassandra supports key/value pair and eventual consistency (based on Amazon’s DynamoDB). Developed by Facebook and implemented in Java Clients are available in Java, PHP, Python, Grails, Ruby, .NET. Used by Facebook, Twitter, Paddy Power, GitHub, and many others. Redis supports key-value pair and a distributed in-memory as well as persistent storage system Started by Salvatore Sanfilippo in 2009 as an independent project Implemented in C Clients are available in PHP, Java, Ruby, Python, C++ etc. Used by Craigslist Sorted Column Family datastore HBase (developed based on Google's bigtable) Created by Powerset and donated to Apache. Implemented in Java. Used by Facebook, Yahoo! and many others. Access method is JRuby, Java, Thrift, REST, ProtoBuf etc. Graph Database Neo4J, FlockDB Neo4J was developed in 2003 and implemented in Java Accessed through REST and Gremlin interfaces. Used by Box.com, ThoughtWorks There are other types of NOSQL databases available as well.
XML Database
Object Database
Grid and Cloud Database
Multimodel Database

12. Eventual Consistency
Consistency – Data should be consistent across user transactions and each client can have the same view of the data
Availability – System should be available always and user can read as well as write always
Partition – System should be partition-tolerant and work in a distributed environment
Eventual Consistency implies BASE (Basically Available, Soft state, Eventual Consistency)
Brewer’s CAP Theorem
Succinctly put, Brewer’s Theorem states that in systems that are distributed or scaled out it’s impossible to achieve all three (Consistency, Availability, and Partition Tolerance) at the same time. You must make trade-offs and sacrifice at least one in favor of the other two.
ACID
BASE
Strong consistency
Weak consistency – stale data OK
Isolation
Availability first
Focus on “commit”
Best effort
Nested transactions
Approximate answers OK
Availability?
Aggressive (optimistic)
Conservative (pessimistic)
Simpler!
Difficult evolution (e. g. schema)
Faster
Easier evolution

13. Eventual Consistency – HAPPY GO LUCKY An example of booking flights for two close friends for attending a conference There is only one ticket left
Data Center
(Asia)
Data Center (US)
Anand
Scott
DATA SYNC-UP
GOOD FRIENDS
bookflighttickets.com
SYNC DOWN
Will the tickets be booked ?
Booking done

14. Brewer’s Theorem was conjectured by Eric Brewer and presented by him (www.cs.berkeley.edu/
~brewer/cs262b-2004/PODC-keynote.pdf) as a keynote address at the ACM Symposium on the
Principles of Distributed Computing (PODC) in 2000.
Brewer’s ideas on CAP developed as a part of his work at UC Berkeley and at Inktomi.
A look at Distributed Update and Replication
Replication
Eventual Consistency – Distributed Environment
A
V0 (V1)
B
V0(V1)
Writes
Reads

15. Theorem of Two options and Three Alternatives SYNCHRONOUS SYNCHRONIZATION
A Single Transaction, Consistency is of prime importance ASYNCHRONOUS SYNCHRONIZATION
Can be achieved but if synchronization fails, no way to know when it happened
Option 1 : Let the Consistency take the precedence and Availability may be compromised considering the system supports partition-tolerance (CP)
Option 2: Let the Availability take the precedence and Consistency may be compromised
considering the system supports partition-tolerance (AP)
Option 3: Let both Consistency and Availability take the precedence and the system is not partition-tolerant (AC)

16. A SMALL TALK COUCHBASE (DOCUMENT) REDIS (KEY-VALUE PAIR) CASSANDRA (COLUMN-FAMILY AND EVENTUAL CONSISTENCY) NEO4J (GRAPH)
HOW WILL WE GO ?
A SMALL OVERVIEW
BASIC FEATURES

17. Features of Couchbase
A high level overview of Couchbase is mentioned below.
1.Stores data in a JSON or binary format in the data store (called a document) 2. Supports basic CRUD operations like get, set, delete etc. Uses MVCC to continue with non-blocking IO for read/writes. 3. Provides a strong layer of caching of data in memory and automatically persists data in file system to support strong failover mechanism 4. Uses concepts like Buckets to group physical resources in a cluster logically with options like setting memory for each bucket as well as replication rule. 5. Each buckets divided in 24 logical partitions called vBuckets and used a cluster map to locate document in a cluster 6. vBuckets the lowest denominator to locate a document in a cluster through hash identifier for each document 7. Asynchronous storing of data in disk and replication data to other servers in a cluster as well as across data-center through XDCR feature 8. Very efficient and easy management of a distributed cluster (horizontal scaling), also known as “Scale Out” 9. Supports integration with Memcache protocol seamlessly 10. Rebalancing of data (documents) through change in the clustering (adding or removing nodes from a cluster and updating cluster map with updated location of documents) 11. Database index like feature through Views for faster access of indexed data 12. Highly secured access to Couchbase server through SASL mechanism 13. Provides the support for both optimistic (through compare and swap - CAS mechanism) and pessimistic locking (through explicit locking) 14. An asynchronous listener based approach for manipulating data through Future interface

18. How does Couchbase work ?

19. More Overview
Replication Process
Smart Client writes the data in server object-managed Cache
Documents is submitted to intra-cluster replication queue for replicating to other servers
The document is persisted to disk write queue asynchronously to write in the disk. The data is written to disk once disk queue flushes off
The data is replicated to other clusters through XDCR once the data in persisted in the disk and eventually indexed for searching. Major Components Data Manager
Object Managed Cache
server warm-up, checkpoint, TAP replicator, backfill, resident item ratio, NRU, ejection, item pager)
Storage Engine
compaction)
Query Engine
Index can be created and queried for JSON documents
Secondary indexes are created through View and Design documents Cluster Manager (orchestration node)
The Hearbeat watchdog
The process Manager
The configuration manager

20. Features of REDIS
A high level overview of Redis is mentioned below.
1.Started in 2009, REDIS (Remote Dictionary Service) is a distributed key-value pair database. A shared memory system for very fast read and write capabilities. Fundamentally, an advanced version of Memcache database. 2. Creator of Redis - Salvatore Sanfilippo termed as “Data Structure Store” capable of storing complex data structure as keys like Set, List, Hash, Sorted Set, bitmaps etc. apart from normal strings. 3. Apart from a data structure store, it also works as blocking queue (Stack) and Publish-Subscribe system 4. A powerful command-line-interface (CLI) and rich API for the clients. 5. An expired based policy can be set for each key-value pair in order to let the list grow unbounded 6. Provides an option to save data in the disk, an unusual case for any key-value system which primarily operates over memory. There is the facility to take the snapshot in an interval based on some criteria like number of changes for keys etc. 7. An additional protection of data through Append-only file for each writes to save from crashing of the server 8. By default, Redis doesn’t provide a good way to handle security of its own. So, its better to use firewall on SSH to protect the secure data. 9. Supports a Master-Slave replication mechanism but not an multi-master scaling and fail-over intelligent system 10. A client managed cluster support through consistent-hashing rather than server side 11. Provides a probabilistic determination of non-existence of data through Bloom filters (managing sequence of bits) 12. Uses a special data structure called “Dynamic String Structure” (SDS) to store all the data internally 13. Uses its own Virtual Memory management to locate data in the disk

21. Replication in REDIS
Master Node
Slave Node
(Read-Write)
Slave Node
(Read-Write)
Slave Node
(Read-only)
Repl
i
cation
Repl
i
cation
Repl
i
cation
Disk
Non-Blocking Synchronization
Redis Server
Redis Client/Smart Client
Periodic Save
Redis uses hash slots to bucketing data elements across nodes, so that data is sharded across nodes for fault-tolerant. If any new node has been added or removed from the cluster, Redis maintains the linkage of data from old to new node through its internal node-to-node communication (ping-pong in Redis’s term) based on binary protocol. Under the hood, Redis also uses a Gossip-based protocol among the nodes to track the status of each node and take necessary actions in case some node went down or not responding. Redis has a smart client who can decide to connect to the right node in the cluster to find the data instead of client to any node arbitrarily.
Gossip
Gossip
A
B
D
C
E

22. An Example of REDIS
Redis can be used for managing data where caching based simple key-value pair along with complex querying facility be given based on the keys.
Analytics
Caching
Search Engine
Messaging
Broker
1.Get a list of cities under a zip code around the world
2.Get a list of books based on ISBN code where each book is associated with multiple “tagging” words
3.Build a sub-system which can browse through a catalog system to find the product data
4.Use a broker to collect data for multiple sources like managing centralized log content Not so good use cases 1. Every bit of data is very precious 2. Multiple master-master setup and failover needed 3. ACID transaction is highly desired 4. Relational data is of prime importance

23. Features of APACHE CASSANDRA
A high level overview of Cassandra is mentioned below. If I had asked people what they wanted, they would have said faster horses. – Henry Ford
1.Influenced by Amazon’s DynamoDB for its distributed design and Google’s Bigtable for the data model, Cassandra is a hybrid datastore supporting both column-family as well as key-value data with Eventual Consistency 2. Cassandra was developed by Facebook and it’s a sparse multi-dimensional hashtable 3. Supports secondary indexes apart from the index on the row-key 4. Supports powerful command-line-interface (CLI) as well as Thrift based multi-lingual drive type communication techniques for the clients.
5.Runs on decentralized mode of keeping each node identical, not like a master-slave topology 6. A tunable consistent system instead of eventual consistency (A always writeble system)
7.Uses Gossip protocol with hinted hands-off to perform peer-to-peer communication across nodes
8.Uses Anti-entropy to manage data synchronization (replication) across multiple nodes with the updated version
9.Uses compaction to merge large datafiles for better management of spaces
10.Uses Bloom filter to find if any element is available in map
11.Uses a concept called “Tombstone” for soft delete. The data is physically deleted during compaction.
12.Uses “Staged Event-Driven Architecture” (SEDA) for highly efficient parallel processing
13.Uses the three separate processes (commit log, memtable, and SSTable) to store and manage data during write operation
14.Uses a concept called “Read Repair” to update outdated values in any node

24. CASSANDRA – Column Family
Suppose A customer has a personal information as well as address. So, two column families can be created, one for personal data and the other for address.
In column family store, data is identified by the row-key. The difference from a RDBMS is that each row can have its own column family data. In case, there are null values for some columns data is not stored there unlike RDBMS tables which consume additional space.

25. CASSANDRA – An Example
Cassandra is a popular datastore for many popular large scale web applications. The following criteria describes some of the important use cases for Cassandra.
High volume writes like tweets from Twitter or comments from Facebook
Don’t need strong consistency
High throughput for Writes
Consistency can be controlled

26. Features of Neo4J
A high level overview of Neo4J is mentioned below.
1.A Graph database (mathematical modeling) for supporting relational information (relationship ) across multiple entities. Developed by Neo technologies.
2.It is built on the concept of nodes, relationship, parameters (key/value pair), and labels
3.A proprietary query named “Cypher” for performing CRUD operations
4.A very high-performing NoSQL database for storing and retrieving connected data
5.Graph is a way to maintain multi-dimensional relation among entities
6.Highly applicable in social networking applications like social graphs, recommendation etc.
7.The Neo4J site provides a rich REPL (Read-eval- print loop) web interface for running queries as well as performing administrative works.
8.It is ACID compliant as well as provides high-availability and master-slave replication across multiple nodes
9.Provides easy client interface through REST and Gremlin
10.Provides fast-look up through Lucene
Sachin
Grapes
Gaurav
Java
Bikram
friend
likes
friend
likes
eats

27. NoSQL – Not mandatory
NoSQL is not a replacement of SQL
Generally NoSQL is not fit for applications which need strong consistency
Correctness of data is more important than availability of data
Transactional context is important than analytical processing
Data is structured and maintained through object relational hierarchy
Need to support Legacy database Future of Databases The future of databases lies with the amalgamation of relational and NoSQL databases based on the need. Pramod J. Sadalage and Martin Fowler mentioned the concept of Polygot Persistence in their famous book “NoSQL Distilled”.

28. Popular Jargons
The following terms are some of the most common and important jargons used in the NoSQL world.
Sharding or Horizontal Scaling
Quorum
Gossip Protocol
Hinted Hands-off
Read Repair
Consistent Hashing
Merkle Tree

29. Useful Links
http://static.googleusercontent.com/media/research.google.com/en//archive/bigtable-osdi06.pdf
Professional NoSQL by Shashank Tiwari
NoSQL Databases by Christof Strauch
Couchbase Server Under the Hood from Couchbase Inc.
http://www.slideshare.net/Muratakal/rdbms-vs-nosql-15797058
http://www.nosql-database.org/
http://www.youtube.com/watch?v=MmL9Lq6WbSY
http://incubator.apache.org/thrift/
http://www.allthingsdistributed.com/2007/10/amazons_dynamo.html
http://www.youtube.com/watch?v=uMxZ4RI6sCQ
http://planetcassandra.org/apache-cassandra-use-cases/
http://www.allthingsdistributed.com/files/amazon-dynamo-sosp2007.pdf
Seven Databases in Seven Weeks by Eric Redmond and Jim R. Wilson