What is the difference between automatic segment space management and manual segment space management?

In a locally managed tablespace, there are two methods that Oracle Database can use to manage segment space: automatic and manual.

Manual segment space management uses linked lists called "freelists" to manage free space in the segment, while automatic segment space management uses bitmaps.

Automatic segment space management is the more efficient method, and is the default for all new permanent, locally managed tablespaces.