TurboIMAGE/XL Database Management System Reference Manual (30391-90012)

Appendix H 687
TurboIMAGE/XL versus TurboIMAGE/V
Control Blocks
Control Blocks
Run-time control blocks are created differently on MPE/iX. A new control block called the
Database User Local Index (DBUX), which is unique to each process, has been added. Also,
four new global tables to monitor system-wide database activity are added. See the
descriptions below for these four tables that were added:
• TURBOLKT
• TURBOGTX
• QOPEN
• QLOCK
Major Differences
Run-time control blocks are no longer created as privileged extra data segments. Instead,
on MPE/iX privileged mapped files are used. If an error occurs when MPE/iX opens a
mapped file, the following error is returned for status code −9:
CANNOT CREATE controlblockname : FILE SYSTEM ERROR nn
where controlblockname is one of the following:
DBS
DBG
DBU
DBR
DBUX
and nn is the number of the file system error. Refer to "Local Database Access" in Chapter
10.
Specifically, control blocks are created as follows:
• The Database System Control Block (DBS) is stored in a permanent mapped file called
TURBODBS.PUB.SYS. It is created as a permanent file and is unique to a system.
DBOPEN creates it if it does not exist and resets it after a system abort.
• The Database Globals Control Block (DBG) and the Database Buffer Area Control
Block (DBB) are stored in a permanent mapped file called DatabaseNameGB which
resides in the same group and account as the database. DatabaseNameGB is created
when the first user opens the database and purged when the last user exits.
• Each Database User Local Control Block (DBU) is stored in an unnamed/new mapped
file. A DBU is created each time a user does a DBOPEN for local database access.
• Each Database Remote Control Block (DBR) is stored in an unnamed/new mapped file.
A DBR is created each time a user does a DBOPEN for remote database access.
• The Database User Local Index Control Block (DBUX) is a new run-time control block