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HBase is an open-source Technology:Column-oriented database modeled after Google's BigTable.

Description

HBase is a database which models data as a multi-dimensional map of strings to an array of bytes. Each entry in a database table is specified by a row key, a column key and a timestamp. Additionally, columns are grouped into column families.

HBase is written in Java and built on top of Technology:Hadoop. Beyond using Java to query HBase, it can also be accessed from a shell using JRuby. A query from the JRuby shell may look like this:

hbase(main):001:0> get 'meganalysis_employees', 'Craig'
COLUMN                    CELL                                                                     
 corporate:salary         timestamp=1347568664910, value=@\xFE$\x00\x00\x00\x00\x00                
 personal:address         timestamp=1347568664910, value=Redmond                                   
 personal:name            timestamp=1347568664910, value=Craig                                     
3 row(s) in 0.0090 seconds

hbase(main):002:0> get 'meganalysis_employees', 'Craig', 'corporate:salary'
COLUMN                    CELL                                                                     
 corporate:salary         timestamp=1347568664910, value=@\xFE$\x00\x00\x00\x00\x00                
1 row(s) in 0.0210 seconds

The get query takes up to four parameters: The target table, the target row key, target column family:column key and a timestamp.

Note that for the employees salary, there is just a string of Unicode escape sequences, because HBase stores only raw bytes and so the double value for the salary is not interpreted by the DB. HBase's Java libraries come with a number of helper functions to convert between byte arrays and other data types to address this.

Since HBase is built on top of it, Technology:Hadoop is used to realize Technology:Data Aggregation meaning, MapReduce jobs can be implemented as a Hadoop worker in plain Java. It is also possible to run Java or JRuby code directly on the database server.

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