HP 3000 Manuals HP 3000 Manuals
ALLBASE/SQL Data Access
The DBEnvironment determines both what data can be accessed in a
transaction and what data can be recovered. Following a failure, a
transaction can be recovered, or all data can be recovered, as follows:
* A transaction is one or more SQL statements that together perform
a unit of work on one or more databases in a DBEnvironment. Work
done within a transaction can be made permanent (committed) or
undone (rolled back).
* After a system or hardware failure, all data within a
DBEnvironment is recovered to a consistent state. Changes
performed by any transactions incomplete at failure time are
rolled back. Changes performed by transactions completed before
failure time are made permanent.
You can have more than one DBEnvironment on your system. When you
connect to a DBEnvironment, ALLBASE/SQL establishes a DBE session for
you. The query processor can process statements only when you are in a
DBE session. You can access any DBEnvironment in either of the two
following modes:
* Single-user mode--only one user or program can use a
DBEnvironment.
* Multiuser mode--more than one user and/or program can use a
DBEnvironment at the same time.