TurboIMAGE/XL Database Management System Reference Manual MPE/iX V6.5 (30391-90011)

Chapter 5 149
TurboIMAGE/XL Library Procedures
DBCONTROL
Discussion
DBCONTROL can be called by a program for the following purposes:
• To enable or disable the AUTODEFER option for the current mode 3 DBOPEN.
• To enable or disable the critical item update option for the current process accessing the
database in mode 1, 3, or 4 depending on the CIUPDATE setting for the database.
• To enable or disable the HWMPUT for the current DBOPEN.
• To include a database in dynamic multiple database transaction.
• To activate deadlock detection for the database.
• To perform B-Tree index related tasks.
In TurboIMAGE/XL default mode, MPE/iX Transaction Management (XM) is used to log
database modifications (DBPUTs, DBDELETEs, DBUPDATEs) to the XM log file. With deferred
output, MPE/iX Transaction Management is not used. Instead, the MPE/iX file system
default mode is used. This mode keeps data pages in memory for as long as possible, either
until file close time or until no more memory is available.
Thus, with deferred output, database modifications caused by calls to DBPUT, DBUPDATE,
or DBDELETE cannot be written to the disk (or can only be partially written). Although
TurboIMAGE/XL generally operates more efficiently in this mode, a system failure while
the database is operating in this mode has a very high probability of causing internal
structural damage to the database.
A program that opens the database exclusively can call DBCONTROL mode 1 to enter the
deferred mode of operation, except when a dynamic transaction is active. In this case, all
database modifications will be kept in memory for as long as possible, either until the
database is closed or until no more memory is available.
A program that opens the database exclusively can call DBCONTROL mode 2 to turn off the
deferred mode of operation. In this case, all database modifications will be written to the
MPE/iX Transaction Management log file until the database is closed.
Programs that are designed to modify the values of detail data set search and sort items
can call DBCONTROL mode 5 if the CIUPDATE setting for a database equals ALLOWED. The
CIUPDATE option is available only in database access modes 1, 3, and 4. The mode 5 call
enables CIUPDATE for only this process until either a DBCONTROL mode 6 call disables the
option for the process or the database is closed. Other processes operating on the same
database are not impacted by these calls.
A program, which must ensure that the values of detail data set search and sort items
remain unchanged for the duration or a portion of the process, can call DBCONTROL mode 6
to disable CIUPDATE if this option has been set to ON for the database, or if the option is
ALLOWED (default or set by DBUTIL) and an earlier call to DBCONTROL mode 5 enabled the
option. CIUPDATE is available only in database access modes 1, 3, and 4. When DBCONTROL
mode 6 is used to disable CIUPDATE, the option is disabled for that process alone until a call
to DBCONTROL mode 5 enables the option for the process or the database is closed. Other
processes operating on the same database are not affected by these calls.