You can reclaim unused storage in a DMS table space by telling the database manager to consolidate in-use extents lower in the table space. This also has the effect of lowering the high water mark. To reduce the container sizes in a DMS table space requires a separate REDUCE operation must also be performed.
To reclaim the unused storage in a DMS table space, you first must initiate an operation to cause extents in the table to be rearranged so as to make use of the free extents lower in the table space. This is done using the LOWER HIGH WATER MARK clause of the ALTER TABLESPACE statement. Next, you can reduce the size of the containers in the table space by a specified amount.
When you reduce the size of containers in a DMS table space, you must specify the names of the containers to reduce, or use the ALL CONTAINERS clause.
Restrictions
The following clauses are not supported with the ALTER TABLESPACE statement when executed in DB2 data sharing environments:
ALTER TABLESPACE ts LOWER HIGH WATER MARK
ALTER TABLESPACE ts REDUCE (ALL CONTAINERS 5 M)
ALTER TABLESPACE ts LOWER HIGH WATER MARK
ALTER TABLESPACE ts REDUCE (FILE "Container1" 2000)