Using The reorg Command

Garbage collection is most effective when you set enable housekeeper GC to 4 or 5.

SAP recommends that you set the parameter value to 5. However, if performance considerations prevent setting this parameter to 4 or 5, and you have an accumulation of empty pages, run reorg on the affected tables. You can obtain statistics on empty pages through the optdiag utility.

When the server is shut down or crashes, requests to deallocate pages that the housekeeper garbage collection task has not yet serviced are lost. These pages, empty but not deallocated by the housekeeper garbage collection task, remain allocated until you remove them by running reorg.

See System Administration Guide: Volume 2 > Using the reorg Command.