An Overview of the NoSQL World - Large Scale and Big Data: Processing and Management - page 317

• Better economics : While RDBMS tends to rely on expensive proprietary

servers and storage systems, NoSQL databases typically use clusters of
cheap commodity servers to manage the exploding data and transaction
volumes. Therefore, the cost per gigabyte or transactions per second for
NoSQL can be many times less than the cost for RDBMS, which allows
a NoSQL setup to store and process more data at a much lower price.
Moreover, when an application uses data that is distributed across hun-
dreds or even thousands of servers, simple economics points to the benefit
of using no-cost server software as opposed to that of paying per-processor
license fees. Once freed from license fees, an application can safely scale
horizontally with complete avoidance of the capital expenses.

• Flexible data models : Even minor changes to the data model of a large

production RDBMS have to be carefully managed and may necessitate
downtime or reduced service levels. NoSQL databases have more relaxed
(if any) data model restrictions. Therefore, application changes and data-
base schema changes can be changed more softly.

These advantages have given NoSQL systems a lot of attractions. However, there
are many obstacles that still need to be overcome before theses systems can appeal
to mainstream enterprises such as:*

• Programming model : NoSQL databases offer few facilities for ad hoc query

and analysis. Even a simple query requires significant programming exper-
tise. Missing the support of declaratively expressing the important join
operation has been always considered one of the main limitations of these
systems.

• Transaction support : Transaction management is one of the powerful fea-

tures of RDBMS. The current limited support (if any) of the transaction
notion from NoSQL database systems is considered as a big obstacle toward
their acceptance in implementing mission critical systems.

• Maturity : RDBMS systems are well known with their high stability and

rich functionalities. In comparison, most NoSQL alternatives are in prepro-
duction versions with many key features either being not stable enough or
yet to be implemented. Therefore, enterprises are still approaching this new
wave with extreme caution.

• Support : Enterprises look for the assurance that if a the 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. Although there are few firms
offering support for each NoSQL database, these companies often are small
start-ups without the global reach, support resources, or credibility of the
key market players such as Oracle, Microsoft, or IBM.

* http://blogs.techrepublic.com.com/10things/?p=1772.