segment
A division within an InnoDB tablespace. If a tablespace is analogous to a directory, the segments are analogous to files within that directory. A segment can grow. New segments can be created.
For example, within a file-per-table tablespace, the table data is in one segment and each associated index is in its own segment. The system tablespace contains many different segments, because it can hold many tables and their associated indexes. The system tablespace also includes up to 128 rollback segments making up the undo log.
Segments grow and shrink as data is inserted and deleted. When a segment needs more room, it is extended by one extent (1 megabyte) at a time. Similarly, a segment releases one extent's worth of space when all the data in that extent is no longer needed.
See also extent.
See also file-per-table.
See also rollback segment.
See also system tablespace.
See also tablespace.
See also undo log.