Database Reference
In-Depth Information
Key-value stores are the simplest NoSQL technologies. All other NoSQL categories build
onthesimplicity,performance,andscalabilityofkey-valuestorestobetterfitsomespecific
use cases.
1.6.2. Column-family stores
The distributed key-value model scaled very well but there was a need to use some sort of
datastructurewithinthatmodel.Thisishowthecolumn-familystorecategorycameonthe
NoSQL scene.
The idea was to group similar values (or columns) together by keeping them in the same
column family (for example, user data or information about topics). Using this approach,
what was a single value in a key-value store evolved to a set of related values. (You can
observe data in a column-family store as a map of maps, or a key-value store where each
value is another map.) The column families are stored in a single file, enabling better read
and write performance on related data. The main goal of this approach was high perform-
ance and high availability when working with big data, so it's no surprise that the leading
technologies in this space are Google's BigTable and Cassandra, originally developed by
Facebook.
1.6.3. Document-oriented databases
A lot of real problems (such as content management systems, user registration data, and
CRM data) require a data structure that looks like a document. Document-oriented data-
basesprovidejustsuchaplacetostoresimple,yetefficientandschemaless,documentdata.
The data structure used in this document model enables you to add self-contained docu-
ments and associative relationships to the document data.
Youcanthinkofdocument-orienteddatabasesaskey-valuestoreswherethevalueisadoc-
ument. This makes it easier to model the data for common software problems, but it comes
at the expense of slightly lower performance and scalability compared to key-value and
column-family stores. The convenience of the object model built into the storage system
is usually a good trade-off for all but massively concurrent use cases (most of us are not
trying to build another Google or Facebook, after all).
