Application processes, concurrency, and recovery

All SQL programs execute as part of an application process. An application process involves the execution of one or more programs, and it is the unit to which DB2® allocates resources and locks.

Different application processes might involve the execution of different programs, or different executions of the same program. The means of initiating and terminating an application process are dependent on the environment.

Locking, commit, and rollback
More than one application process might request access to the same data at the same time. Furthermore, under certain circumstances, an SQL statement can execute concurrently with a utility on the same table space. Locking is used to maintain data integrity under such conditions, preventing, for example, two application processes from updating the same row of data simultaneously.
Unit of work
A unit of work is a recoverable sequence of operations within an application process. A unit of work is sometimes called a logical unit of work.
Unit of recovery
A DB2 unit of recovery is a recoverable sequence of operations executed by DB2 for an application process.
Rolling back work
DB2 can back out all changes made in a unit of recovery or only selected changes. Only backing out all changes results in a point of consistency.
Packages and application plans
A package contains control structures that DB2 uses when it runs SQL statements. An application plan relates an application process to a local instance of DB2 and specifies processing options.

Parent topic: Application processes and transactions

Parent topic: DB2 for z/OS and SQL concepts