RTFM

Does garbage collection occur in the data files and indexes? For example, is space from deleted records recovered or reused?

Yes, space from deleted records is re-used on subsequent inserts. Space in files is never de-allocated back to disk. If index balancing is turned on, then unused space in index pages is also re-used. See Rebuild Utility Concepts in Advanced Operations Guide for information about using the Rebuild utility.


Rebuild Utility
Remove deleted record space from a file, change the page size, or add system data.