Columns in Apache HBase are grouped into column families.
All column members of a column family have the same prefix. For example, the
columns courses:history and
courses:math are both members of the
courses column family.
The colon character (
:) delimits the column family from the
The column family prefix must be composed of
printable characters. The qualifying tail, the
column family qualifier, can be made of any
arbitrary bytes. Column families must be declared up front
at schema definition time whereas columns do not need to be
defined at schema time but can be conjured on the fly while
the table is up an running.
Physically, all column family members are stored together on the filesystem. Because tunings and storage specifications are done at the column family level, it is advised that all column family members have the same general access pattern and size characteristics.