This will defragment the tablespace named TABLESPACE.
Over time, if you create and drop database objects, and/or insert and delete records, the usage of a tablespace will become fragmented. Between any two used fragments there will be an unused fragment. This command will “coalesce” the used fragments into a single chunk, thus freeing-up the unused fragments.
Cons: You need DBA privileges to execute this command. Sometimes there will be no increase in available space because the tablespace was not sufficiently fragmented in the first place.