HBase - Hadoop: The Definitive Guide - page 698

HBasics
HBase is a distributed column-oriented database built on top of HDFS. HBase is the Ha-
doop application to use when you require real-time read/write random access to very large
datasets.
Although there are countless strategies and implementations for database storage and re-
trieval, most solutions — especially those of the relational variety — are not built with very
large scale and distribution in mind. Many vendors offer replication and partitioning solu-
tions to grow the database beyond the confines of a single node, but these add-ons are gen-
erally an afterthought and are complicated to install and maintain. They also severely com-
promise the RDBMS feature set. Joins, complex queries, triggers, views, and foreign-key
constraints become prohibitively expensive to run on a scaled RDBMS, or do not work at
all.
HBase approaches the scaling problem from the opposite direction. It is built from the
ground up to scale linearly just by adding nodes. HBase is not relational and does not sup-
port SQL, [ 136 ] but given the proper problem space, it is able to do what an RDBMS cannot:
host very large, sparsely populated tables on clusters made from commodity hardware.
The canonical HBase use case is the webtable , a table of crawled web pages and their at-
tributes (such as language and MIME type) keyed by the web page URL. The webtable is
large, with row counts that run into the billions. Batch analytic and parsing MapReduce
jobs are continuously run against the webtable, deriving statistics and adding new columns
of verified MIME-type and parsed-text content for later indexing by a search engine. Con-
currently, the table is randomly accessed by crawlers running at various rates and updating
random rows while random web pages are served in real time as users click on a website's
cached-page feature.
Backdrop
The HBase project was started toward the end of 2006 by Chad Walters and Jim Kellerman
at Powerset. It was modeled after Google's Bigtable, which had just been published. [ 137 ] In
February 2007, Mike Cafarella made a code drop of a mostly working system that Jim
Kellerman then carried forward.
The first HBase release was bundled as part of Hadoop 0.15.0 in October 2007. In May
2010, HBase graduated from a Hadoop subproject to become an Apache Top Level Project.
Today, HBase is a mature technology used in production across a wide range of industries.