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.