In a database management system, a tablespace is a logical container that stores data. A tablespace can contain multiple data files, and each data file belongs to a single tablespace. The size of a tablespace is the total size of all the data files in the tablespace.
Checking the size of a tablespace is important for performance tuning and capacity planning. If a tablespace is too small, it can cause performance problems. If a tablespace is too large, it can waste storage space.