Databases Reference
In-Depth Information
Key
Value
image-12345.jpg
Binary image file
Image name
http://www.example.com/my-web-
page.html
HTML of a web page
Web page URL
N:/folder/subfolder/myfile.pdf
PDF document
File path name
9e107d9d372bb6826bd81d3542a419d6
The quick brown fox jumps
over the lazy dog
MD5 hash
view-person?person-
id=12345&format=xml
<Person><id>12345</id
.</Person>
REST web service call
SELECT PERSON FROM PEOPLE
WHERE PID="12345"
<Person><id>12345</id
.</Person>
SQL query
Figure 4.2
Sample items in a key-value store. A key-value store has a key that's
associated with a value. Keys and values are flexible. Keys can be image names, web
page URLs, or file path names that point to values like binary images, HTML web pages,
and PDF documents.
The many names of a key-value store
A key-value store has different names depending on what system or programming lan-
guage you're using. The process of looking up a stored value using an indexed key
for data retrieval is a core-data access pattern that goes back to the earliest days of
computing. A key-value store is used in many different computing systems but wasn't
formalized as a data architecture pattern until the early 1990s. Popularity increased
in 1992, when the open source Berkley DB libraries popularized it by including the
key-value store pattern in the free UNIX distribution. Key-value store systems are
sometimes referred to as
key-data stores
, since any type of byte-oriented data can be
stored as the value. For the application programmer, a structure of an array with two
columns is generally called an
associative array
or
map
, and each programming lan-
guage may call it something slightly different—a hash, a dictionary, or even an object.
The current convention, and this text, uses the term key-value store. For more on the
history of Berkeley DB, see
http://mng.bz/kG9c
.
4.1.2
Benefits of using a key-value store
Why are key-value stores so powerful, and why are they used for so many different pur-
poses? To sum it up: their simplicity and generality save you time and money by mov-
ing your focus from architectural design to reducing your data services costs through
Precision service levels
Precision service monitoring and notification
Scalability and reliability
Portability and lower operational costs
