The free space reusage facility uses the free space on used pages by switching the page search mode to the free page reuse mode once the number of a table's used segments reaches the number of user-specified segments and those segments have all become full. If there is no free space in any of the specified number of segments, it switches to the new page allocate mode for allocation of a new unused segment.
When no segment count has been specified, the free page reuse mode is used when there are no more unused pages in the RDAREA.
When there are no more unused pages in the RDAREA, search efficiency is better in the free page reuse mode when the free space reusage facility is used than when it is not used. In free page reuse mode, the next search position is remembered and subsequent searches are performed from there. If this facility is not used, searches always start from the beginning.
Note that if the free space reusage facility is not used, operations always use the new page allocate mode. In this case, performance will drop significantly when there are no more unused segments. To prevent this, increase the number of unused segments, such as by reorganizing the table or by releasing used free pages and used free segments.
The following figure provides an overview of the free space reusage facility.
Figure 14-4 Overview of the free space reusage facility