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

492 Chapter10
Internal Structures and Techniques
Run-Time TurboIMAGE/XL Control Blocks
The TURBOGTX is a permanent file, TURBOGTX.PUB.SYS, that is created by DBXBEGIN (if it
does not exist beforehand). Thereafter, it is opened for all users who employ dynamic
multi-database transaction(s) (DMDBX). Each system has only one TURBOGTX file, and it
remains on the system even after the system is rebooted. It is used for tracking DMDBX.
The QOPEN table is an unnamed global object and is first created by DBOPEN when the first
writer of any database enabled for user logging opens a database. It is subsequently
accessed only by writers of databases enabled for user logging. Each system has only one
QOPEN table, and it is purged when all processes accessing it are terminated. It contains
information pertaining to user logging process for DBOPEN. This information is used to
write to log records for DBRECOV and to coordinate with DBQUIESCE called by
TurboSTORE/iX 7x24 True-Online Backup.
The QLOCK is an unnamed permanent global structure that is created by DBOPEN (if it does
not exist beforehand). There is one per system, and it is accessed by all writers to all
databases. It is purged only at system reboot time. It is used for containing database
information required to quiesce database(s) for TurboSTORE/iX 7x24 True-Online
Backup.
Remote Database Access
TurboIMAGE/XL provides the capability of accessing a database on a remote HP 3000
system from a user program running on the local HP 3000 system, as described in
chapter 9. This capability is provided in conjunction with NS3000/XL and is accomplished
by transmitting TurboIMAGE/XL database access requests (DBGET, DBPUT, and so forth)
to the remote computer where they are executed and the results returned to the local
calling process. The control block structures used by TurboIMAGE/XL for the remote
computer which contains the database are those described in the preceding section.
On the local computer running the user application program, TurboIMAGE/XL constructs
and uses a structure called the Remote Database Control Block (DBR). One DBR is created
each time a user's process issues a DBOPEN accessing a remote TurboIMAGE/XL database
(each access path to a remote database); this DBR is released when the corresponding
DBCLOSE is issued. The DBR resides in a privileged, unnamed temporary file associated
with the user application process on the local computer, and contains database, set, and
item information plus the work areas necessary to set up communication with the remote
computer. Returned data and status information is also processed in the DBR and is
transferred to the appropriate user stack areas before TurboIMAGE/XL returns to the
local calling process.
Access to a TurboIMAGE/V database from an MPE/iX system or access to a
TurboIMAGE/XL database from an MPE V system is allowed provided both systems are
configured with Network Services (NS3000). To access an IMAGE/3000 database, an MPE
V system (with NS/3000 and TurboIMAGE/V) acting as an intermediary is required.
However, if the limits on the remote database exceed those allowed on the local system,
access will not be successful. This is because the DBR will be too small to handle remote
capacities that exceed the local limits.