TurboIMAGE/XL Database Management System Reference Manual MPE/iX V6.5 (30391-90011)
Chapter 8 411
Using the Database Utilities
DBUNLOAD
n
is the number of the volume.
y
is the number of write errors from which DBUNLOAD has successfully
recovered.
z
is the logical device number of the unit.
DBUNLOAD is necessary if you want to modify the database structure to, for example,
increase the capacity of a data set. To increase a capacity,
1. Unload the entries.
2. Purge the database.
3. Change the schema and create a new root file.
4. Execute the DBUTIL >>CREATE command.
5. Reload the data entries from the volumes created by DBUNLOAD.
The data sets are unloaded in the order that they were defined in the original schema. No
data set names are recorded on the backup volume(s); entries are merely associated with
the corresponding data set from which they are read. DBUNLOAD calls the DBGET procedure
to read each entry from each set of the database and, to read the complete entry, uses a list
parameter of an at-sign followed by a semicolon (@;). Values for data items appear in each
entry in the same order as the items were mentioned in the data set definition in the
schema. The language ID is copied along with the data of the database.
DBUNLOAD requires exclusive access to the database. If the database is already open by any
other process, DBUNLOAD prints the message:
DATABASE IN USE
and prompts again for a database name.
DBUNLOAD operates in either serial or chained mode as explained below. The mode is
determined by the entry point specified with the RUN command; for example:
:RUN DBUNLOAD.PUB.SYS,CHAINED
The default entry, if none is specified, is chained.
• In serial mode, DBUNLOAD copies the data entries serially in record number order.
"Stand-alone" detail data sets, those which are not tied to any master data sets through
specified search item paths, are always unloaded serially.
• In chained mode, DBUNLOAD copies all of the detail entries with the same primary path
search item value to contiguous locations on the backup file. The ordering of the search
item values from the primary path is based on the physical order of the matching value
in the associated master data set. Figure 8-1. (shown at the end of this section on
DBUNLOAD) illustrates the method for unloading a data set in chained mode. After the
database is reloaded, chained access along the primary path is more efficient.