15.9.3 Reusing used free segments

Organization of this subsection
(1) Releasing used free segments
(2) Benefits of releasing used free segments
(3) Method of operation

(1) Releasing used free segments

By executing the free page release utility, you can convert used free segments to unused segments and reuse them. This is called releasing used free segments. Figure 15-4 provides an overview of releasing used free segments.

Figure 15-4 Releasing used free segments

[Figure]

(2) Benefits of releasing used free segments

Once segments are allocated, only the table (or index) that is assigned to use a particular segment can use it; no other tables can do so. Releasing used free segments converts used free segments to unused segments, which enables other tables to use those segments.

(3) Method of operation

Whether or not to release used free segments is determined from the execution results of the free page release utility or the database condition analysis utility. Release used free segments if there are a large number of them.

(a) Estimate the system log file capacity

Because updated logs of the database are obtained when used free segments are released, we recommend that you re-estimate the system log file capacity. For details about estimating system log file capacity, see the manual HiRDB Version 8 Installation and Design Guide.

(b) Execute the free page release utility

You use the free page release utility to release used free segments. Check the execution results of the free page release utility to determine if used free segment have been released as expected.

Reference note
A table or index whose used free segments are being released (the free page release utility is executing) cannot be accessed. Because of this, any UAP that attempts to access an RDAREA being processed is placed in wait status. To have the utility return an error without such a UAP being placed in wait status, use the pdhold command to shut down the RDAREA before executing the utility.
(c) If the free page release utility terminates abnormally

If the free page release utility terminates abnormally, the system returns to its status before the utility was executed (before any operation was performed). In such a case, simply re-execute the free page release utility. Although not re-executing the free page release utility does not create a problem, no used free segments are released if you do not re-execute.