10.4. Managing Extent Usage

An extent in Oracle parlance is the size of the chunks of storage that are allocated to a table or index upon creation or when that table or index needs to be extended to accommodate more data. Extent management was always a problem in older versions of Oracle because it could never be precisely controlled.

With the advent of locally managed tablespaces (LMTs) in Oracle8i, Oracle has greatly simplified space management. LMTs allow DBAs to control the extent sizes allocated for tablespace objects, regardless of their STORAGE specifications. This eliminates the fragmentation that can occur in dictionary-managed tablespaces when objects are created with different extent sizes. Such fragmentation is impossible when LMTs are used. With LMTs, the extent size can be controlled so that all tablespace extents are the same size. In this section, we'll look at the benefits of LMTs and then see how the toolkit script maxext.pl can make this feature even more effective.