NoSQL, which most now take to mean “Not Only SQL,” is a new non-relational approach to data management that supports dynamic and flexible schemas, optimized storage for web scale, and extreme performance as well as makes semi-structured and unstructured data easier to use and access. Although RDBMS technology is still a good fit for critical transactional applications, new types of applications are motivating architects to look elsewhere when the relational approach falls short. Craigslist, Facebook, Twitter, Yahoo, and YouTube have already used NoSQL to support demanding web-scale applications. Although adoption of NoSQL in enterprises is around 4%, Forrester expects this to double in the next two years and that by 2015, 20% of enterprises will use NoSQL to support some or all of their applications. This is one of the major reasons for choosing to use NoSQL.

NoSQL offers several benefits in the areas of data management, access, storage, scale, and performance that make it a viable alternative to RDBMS. NoSQL delivers:

Flexible schema structures to support new types of applications.
Unlike an RDBMS, which requires the application developer to predefine data attributes, entities, and relationships, NoSQL offers a more flexible approach in which the application rather than the data store defines the schema and access paths. NoSQL supports a wide range of new data types, including textual types such as JSON as well as many other unstructured and semistructured data types. NoSQL’s inclusion of these flexible schemas and data types makes it easier to build new types of social media, cloud, and other scale-out applications.

High-performance key-value data reads and writes.
Applications that require extensive data reads and writes often experience excessive latency due to disk input/output (I/O) bottlenecks, especially when the app has high volumes of both. NoSQL approaches are efficient at reading very large amounts of data in a scale-out model, with each node in a cluster having its own I/O channels and controllers to deliver linear scale. For example, Twitter spreads accounts across thousands of nodes using a key-value store, and millions of users get low latency while concurrently accessing data. Conversely, NoSQL is not well suited to joining entities unless the store contains prejoined data.

Elastic scale to support dynamic workloads.
Because of the need to partition data across multiple databases, it’s challenging to scale out an RDBMS to handle growth. This makes it challenging to use an RDBMS when building an application that can easily scale from a thousand to a million users. NoSQL’s shared-nothing, scale-out architecture makes it easy to add nodes in a cluster or cloud to deliver linear scale.

High-performance key-value data reads and writes.
Applications that require extensive data reads and writes often experience excessive latency due to disk input/output (I/O) bottlenecks, especially when the app has high volumes of both. NoSQL approaches are efficient at reading very large amounts of data in a scale-out model, with each node in a cluster having its own I/O channels and controllers to deliver linear scale. For example, Twitter spreads accounts across thousands of nodes using a key-value store, and millions of users get low latency while concurrently accessing data. Conversely, NoSQL is not well suited to joining entities unless the store contains prejoined data.

Elastic scale to support dynamic workloads.
Because of the need to partition data across multiple databases, it’s challenging to scale out an RDBMS to handle growth. This makes it challenging to use an RDBMS when building an application that can easily scale from a thousand to a million users. NoSQL’s shared-nothing, scale-out architecture makes it easy to add nodes in a cluster or cloud to deliver linear scale.

Freedom to innovate.
NoSQL is for application developers and programmers who want complete control and flexibility to store and access data in the manner they want without having to comply with the constraints and rigid structures an RDBMS imposes.

Five challenges of NoSQL
The promise of the NoSQL database has generated a lot of enthusiasm, but there are many obstacles to overcome before they can appeal to mainstream enterprises. Here are a few of the top challenges.

Maturity
RDBMS systems have been around for a long time. NoSQL advocates will argue that their advancing age is a sign of their obsolescence, but for most CIOs, the maturity of the RDBMS is reassuring. For the most part, RDBMS systems are stable and richly functional. In comparison, most NoSQL alternatives are in pre-production versions with many key features yet to be implemented. Living on the technological leading edge is an exciting prospect for many developers, but enterprises should approach it with extreme caution.

Support
Enterprises want the reassurance that if a key system fails, they will be able to get timely and competent support. All RDBMS vendors go to great lengths to provide a high level of enterprise support. In contrast, most NoSQL systems are open source projects, and although there are usually one or more firms offering support for each NoSQL database, these companies often are small start-ups without the global reach, support resources, or credibility of an Oracle, Microsoft, or IBM.

Analytics and business intelligence
NoSQL databases have evolved to meet the scaling demands of modern Web 2.0 applications. Consequently, most of their feature set is oriented toward the demands of these applications. However, data in an application has value to the business that goes beyond the insert-read-update-delete cycle of a typical Web application. Businesses mine information in corporate databases to improve their efficiency and competitiveness, and business intelligence (BI) is a key IT issue for all medium to large companies. NoSQL databases offer few facilities for ad-hoc query and analysis. Even a simple query requires significant programming expertise, and commonly used BI tools do not provide connectivity to NoSQL. Some relief is provided by the emergence of solutions such as HIVE or PIG, which can provide easier access to data held in Hadoop clusters and perhaps eventually, other NoSQL databases.

Administration
The design goals for NoSQL may be to provide a zero-admin solution, but the current reality falls well short of that goal. NoSQL today requires a lot of skill to install and a lot of effort to maintain.

Expertise
There are literally millions of developers throughout the world, and in every business segment, who are familiar with RDBMS concepts and programming. In contrast, almost every NoSQL developer is in a learning mode. This situation will address naturally over time, but for now, it’s far easier to find experienced RDBMS programmers or administrators than a NoSQL expert.

References
[1] Stonebraker, M. “SQL databases v. NoSQL databases.” Commun. ACM 53(4) (April 2010), pp. 10 – 11.
[2] Leavitt, N., “Will NoSQL Databases Live Up to Their Promise?,” Computer , 43(2), Feb. 2010 pp.12 – 14.
[3] Yuhanna, N., “NoSQL Offers New Options for Application Developers”, Forrester Research, September 2011, ID: 60237
[4] Hopkins, B., “Big Opportunities in Big Data”, Forrester Research, May 2011, ID: 59321