Accounting for processor usage in a CICS DB2 environment

The processor times reported in the DB2® accounting records are the TCB time for the thread TCB running code in CICS® or in the DB2 address space, using cross-memory services; and the SRB time for work scheduled in CICS.

The DB2 accounting trace can be started with CLASS 1, CLASS 2, or CLASS 3. However, CLASS 1 must always be active to externalize the information collected by activating CLASS 2, CLASS 3, or both classes. CLASS 1 (the default) results in accounting data being accumulated by several DB2 components during normal execution. This data is then collected to write the DB2 accounting record. The data collection does not involve any overhead of individual event tracing. CLASS 2 and CLASS 3 activate many additional trace points. Every occurrence of these events is traced internally, the additional total statistics computed and written to the DB2 accounting record.

For accounting CLASS 1, a task processor timer is created when the task control block (TCB) is attached. When a thread to DB2 starts, the timer value is saved. When the thread is terminated (or the authorization ID is changed), then the timer is checked again. Both the timer start and end values are recorded in the DB2 accounting record.

For accounting CLASS 2, the timer is checked on every entry and exit from DB2 to record the 'IN DB2' time in the DB2 accounting record. In this case, it is the difference that is stored in the record.

For accounting CLASS 3, the I/O elapsed time and lock and latch suspension time spent 'IN DB2' are collected and written to the DB2 accounting record.


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