UNIT I Introduction to

NoSQL

1
 Agenda
• Understanding NoSQL Databases,

• History of NoSQL

• Features of NoSQL- Scalability, Cost, Flexibility

• NoSQL Business Drivers

• Classification and Comparison of NoSQL Databases

• Consistency – Availability - Partitioning (CAP)

• Limitations of Relational Databases

• Comparing NoSQL with RDBMS

• Managing Different Data Types

• Key-Value Stores, Document

Understanding NoSQL Database

• NoSQL stands for:

• No Relational
• No RDBMS
• Not Only SQL
• NoSQL is an umbrella term for all databases and data stores that
don’t follow the RDBMS principles
• A collection of several (related) concepts about data storage and manipulation
• Often related to large data sets
NoSQL Definition
From www.nosql-database.org:
Next Generation Databases mostly
addressing some of the points: being non-
relational, distributed, open-source and
horizontal scalable.

The original intention has been modern

web-scale databases. The movement began
early 2009 and is growing rapidly.

Often more characteristics apply as:

schema-free, easy replication support,
simple API, eventually consistent / BASE
(not ACID), a huge data amount, and more.
History of NoSQL

• Non-relational DBMSs are not new

• But NoSQL represents a new incarnation
• Due to massively scalable Internet applications
• Based on distributed and parallel computing
• Development
• Starts with Google
• First research paper published in 2003
• Continues also thanks to Lucene's developers/Apache (Hadoop) and Amazon
(Dynamo)
• Then a lot of products and interests came from Facebook, Netflix, Yahoo, eBay,
Hulu, IBM, and many more
History of NoSQL

• Three major papers were the seeds of the NoSQL movement

• BigTable (Google)
• Dynamo (Amazon)
• Distributed key-value data store
• Eventual consistency
• CAP Theorem (discuss in a sec ..)
NoSQL and Big Data

• NoSQL comes from Internet, thus it is often related to the “big

data” concept
• How much big are “big data”?
• Over few terabytes Enough to start spanning multiple storage units
• Challenges
• Efficiently storing and accessing large amounts of data is difficult, even more
considering fault tolerance and backups
• Manipulating large data sets involves running immensely parallel processes
• Managing continuously evolving schema and metadata for semi-structured and
un-structured data is difficult
How did we get here?

• Explosion of social media sites (Facebook, Twitter) with large

data needs
• Rise of cloud-based solutions such as Amazon S3 (simple
storage solution)
• Just as moving to dynamically-typed languages (Python, Ruby,
Groovy), a shift to dynamically-typed data with frequent
schema changes
• Open-source community
Limitations of Relational Databases

• The context is Internet

• RDBMSs assume that data are
• Dense
• Largely uniform (structured data)
• Data coming from Internet are
• Massive and sparse
• Semi-structured or unstructured
• With massive sparse data sets, the typical storage mechanisms
and access methods get stretched
Limitations of Relational Databases
• Issues with scaling up when the dataset is just too big
• RDBMS were not designed to be distributed
• Traditional DBMSs are best designed to run well on a
“single” machine
• Larger volumes of data/operations requires to upgrade the server with faster
CPUs or more memory known as ‘scaling up’ or ‘Vertical scaling’
• NoSQL solutions are designed to run on clusters or multi-
node database solutions
• Larger volumes of data/operations requires to add more machines to the
cluster, Known as ‘scaling out’ or ‘horizontal scaling’
• Different approaches include:
• Master-slave
• Sharding (partitioning)
Limitations of Relational Databases

• Master-Slave
• All writes are written to the master. All reads performed against
the replicated slave databases
• Critical reads may be incorrect as writes may not have been
propagated down
• Large data sets can pose problems as master needs to
duplicate data to
• Sharding
• Any DB distributed across multiple machines needs to
know in what machine a piece of data is stored or must
be stored
• A sharding system makes this decision for each row, using
its key
 Features of NoSQL
• Large data volumes • Asynchronous Inserts &
• Google’s “big data” Updates
• Scalable replication • Schema-less
and distribution • ACID transaction
• Potentially thousands of properties are not needed
machines – BASE
• Potentially distributed • CAP Theorem
around the world • Open source development
• Queries need to return
answers quickly
• Mostly query, few
updates
NoSQL Database Types

Discussing NoSQL databases is complicated

because there are a variety of types:

•Sorted ordered Column Store

•Optimized for queries over large datasets, and store
columns of data together, instead of rows
•Document databases:
•pair each key with a complex data structure known as a document.
•Key-Value Store :
•are the simplest NoSQL databases. Every single item in the database is stored as
an attribute name (or 'key'), together with its value.
•Graph Databases :
•are used to store information about networks of data, such as social connections.
Document Databases (Document
Store)
• Documents
• Loosely structured sets of key/value pairs in documents, e.g., XML, JSON,
BSON
• Encapsulate and encode data in some standard formats or encodings
• Are addressed in the database via a unique key
• Documents are treated as a whole, avoiding splitting a document into its
constituent name/value pairs
• Allow documents retrieving by keys or contents
• Notable for:
• MongoDB (used in FourSquare, Github, and more)
• CouchDB (used in Apple, BBC, Canonical, Cern, and more)
Document Databases (Document Store)

• The central concept is the notion of a "document“ which corresponds to a

row in RDBMS.
• A document comes in some standard formats like JSON (BSON).
• Documents are addressed in the database via a unique key that represents
that document.
• The database offers an API or query language that retrieves documents
based on their contents.
• Documents are schema free, i.e., different documents can have structures
and schema that differ from one another. (An RDBMS requires that each
row contain the same columns.)

15
 Document Databases, JSON
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Key/Value stores
• Store data in a schema-less way
• Store data as maps
• HashMaps or associative arrays
• Provide a very efficient average running
time algorithm for accessing data
• Notable for:
• Couchbase (Zynga, Vimeo, NAVTEQ, ...)
• Redis (Craiglist, Instagram, StackOverfow,
flickr, ...)
• Amazon Dynamo (Amazon, Elsevier,
IMDb, ...)
• Apache Cassandra (Facebook, Digg,
Reddit, Twitter,...)
• Voldemort (LinkedIn, eBay, …)
• Riak (Github, Comcast, Mochi, ...)
Sorted Ordered Column-Oriented
Stores
• Data are stored in a column-oriented way
• Data efficiently stored
• Avoids consuming space for storing nulls
• Columns are grouped in column-families
• Data isn’t stored as a single table but is stored by column families
• Unit of data is a set of key/value pairs
• Identified by “row-key”
• Ordered and sorted based on row-key

• Notable for:
• Google's Bigtable (used in all
Google's services)
• HBase (Facebook, StumbleUpon,
Hulu, Yahoo!, ...)
Graph Databases

• Graph-oriented
• Everything is stored as an edge, a node or an attribute.
• Each node and edge can have any number of attributes.
• Both the nodes and edges can be labelled.
• Labels can be used to narrow searches.

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NoSQL, No ACID

• RDBMSs are based on ACID (Atomicity, Consistency,

Isolation, and Durability) properties
• NoSQL
• Does not give importance to ACID properties
• In some cases completely ignores them
• In distributed parallel systems it is difficult/impossible to
ensure ACID properties
• Long-running transactions don't work because keeping resources
blocked for a long time is not practical
BASE Transactions

• Acronym contrived to be the opposite of ACID

• Basically Available,
• Soft state,
• Eventually Consistent
• Characteristics
• Weak consistency – stale data OK
• Availability first
• Best effort
• Approximate answers OK
• Aggressive (optimistic)
• Simpler and faster
 CAP Theorem
A congruent and logical way for assessing the problems involved in
assuring ACID-like guarantees in distributed systems is provided by the
CAP theorem
At most two of the following three can be maximized at one time
• Consistency
• Each client has the same view of the
data
• Availability
• Each client can always read and write
• Partition tolerance
• System works well across distributed
physical networks
 CAP Theorem: Two out of Three
• CAP theorem – At most two properties on three can be
addressed
• The choices could be as follows:

1. Availability is compromised but consistency and partition

tolerance are preferred over it
2. The system has little or no partition tolerance. Consistency
and availability are preferred
3. Consistency is compromised but systems are always
available and can work when parts of it are partitioned
Consistency or Availability
• Consistency and Availability is not
“binary” decision

C A
• AP systems relax consistency in
favor of availability – but are not
inconsistent

• CP systems sacrifice availability for

consistency- but are not unavailable
P
• This suggests both AP and CP
systems can offer a degree of
consistency, and availability, as
well as partition tolerance
Performance
• There is no perfect NoSQL database
• Every database has its advantages and disadvantages
• Depending on the type of tasks (and preferences) to accomplish
• NoSQL is a set of concepts, ideas, technologies, and software
dealing with
• Big data
• Sparse un/semi-structured data
• High horizontal scalability
• Massive parallel processing
• Different applications, goals, targets, approaches need
different NoSQL solutions
 Where would I use it?

• Where would I use a NoSQL database?

• Do you have somewhere a large set of uncontrolled, unstructured,
data that you are trying to fit into a RDBMS?
• Log Analysis
• Social Networking Feeds (many firms hooked in through Facebook or
Twitter)
• External feeds from partners
• Data that is not easily analyzed in a RDBMS such as time-based data
• Large data feeds that need to be massaged before entry into an
RDBMS
 Don’t forget about the DBA
• It does not matter if the data is deployed on a NoSQL
platform instead of an RDBMS.
• Still need to address:
• Backups & recovery
• Capacity planning
• Performance monitoring
• Data integration
• Tuning & optimization
• What happens when things don’t work as expected and
nodes are out of sync or you have a data corruption
occurring at 2am?
• Who you gonna call?
• DBA and SysAdmin need to be on board
The Perfect Storm

• Large datasets, acceptance of alternatives, and dynamically-

typed data has come together in a perfect storm
• Not a backlash/rebellion against RDBMS
• SQL is a rich query language that cannot be rivaled by the
current list of NoSQL offerings
• So you have reached a point where a read-only cache and write-based
RDBMS isn’t delivering the throughput necessary to support a particular
application.
• You need to examine alternatives and what alternatives are out there.
• The NoSQL databases are a pragmatic response to growing scale of databases
and the falling prices of commodity hardware.
Summary

• Most likely, 10 years from now, the majority of data is still stored in
RDBMS.
• Leading users of NoSQL datastores are social networking
sites such as Twitter, Facebook, LinkedIn, and Digg.
• Not every problem is a nail and not every solution is a
hammer.
• NoSQL has taken a field that was "dead" (database development) and
suddenly brought it back to life.