While the instance maintains all of its information about the database in memory in the SGA, the database itself is stored on disk. The tablespaces are composed of datafiles, which are operating system files or raw partitions. Each segment is stored in a tablespace. You have some flexibility in that datafiles can be configured to AUTOEXTEND if the tablespace runs out of room, and segments can be set to have an UNLIMITED number of extents. However, there is always a practical limit in that a datafile cannot AUTOEXTEND if there is no more space left in the filesystem, and a segment cannot grow past the available free space in a tablespace.

In the next section, we provide a set of SQL queries that track storage utilization in the database over time.