(Quelle: IBM Hotline News 2005)

http://www-1.ibm.com/support/docview.wss?rs=64&context=SSEPEK&dc=DB520&uid=swg21045823&loc=en_US&cs=utf-8&lang=en

Problem: What is DB2 Accounting Class 2 Not Accounted Time?

Solution: The following simple formula defines DB2® Class 2 Not Accounted Time:

DB2 Class 2 Not Accounted Time =

DB2 Class 2 Elapsed time - (DB2 Class 2 CPU time + DB2 Class 3 suspension time)

Usually the DB2 Class 2 Not Accounted time is very small or negligible. It represents time that DB2 is unable to account for. If you see significant DB2 Class 2 Not Accounted time, it could be due to one of the following reasons:

• In some cases, high DB2 Class 2 Not Accounted time is caused by too much detailed online tracing or bugs in some vendor performance monitors.

Reduce the level of tracing or stop the vendor performance monitor to help reduce the Not Accounted time to an acceptable level. This situation is usually the primary cause of high not-accounted-for-time on systems that are not CPU-constrained.

• In a non-data sharing environment, it could be due to running on a very high CPU utilization environment and waiting for CPU cycles, especially with lower dispatching priority in Work Load Manager goal mode.

A non-dedicated LPAR can be interrupted by another LPAR and lose the processor for some time.

• Also in a non-data sharing environment, it could be due to running in a high MVS™ paging environment and waiting for storage allocation. If DB2 gets swapped out by losing control of the processor or waiting for a processor, this increased time is the result.
• In a data sharing environment, prior to V7, it could be due to asynchronous coupling facility requests. For example, group buffer pool requests for > 4KB pages, long running coupling facility commands such as 'Read Directory Info' and 'Delete Name under mask', or conversion of synchronous requests to asynchronous requests due to a coupling facility subchannel busy condition. In V7 or later, the coupling facility suspensions due to asynchronous requests are shown under a new category called 'Asynch IXL Requests' in DB2 performance monitor. If the asynchronous write to the secondary group buffer pool (GBP) does not complete before synchronous write to the primary GBP with GBP duplexing, not accounted time can be the result.
• Not accounted time can be the wait time for return from requests to be returned from VTAM® or TCP/IP.
• Instrumentation Facility Interface (IFI) log read can cause not accounted time.
• If the environment is very I/O intensive, the Media Manager might be running out of request blocks.
• z/OS® events can cause not accounted time, such as SRM timer pops, for example when an SMF SRB is triggered to collect open data set statistics.
• Waiting for package accounting can result in not accounted time.
• Not accounted time can be accounted for by a PREPARE which is not found in the Dynamic Statement Cache.
• Waiting for a page being moved from VP to HP can result in not accounted time.
• DD consolidation (z/OS parameter DDCONS=YES DETAIL) has overhead that is not accounted. See DDCONS informational APAR II07124.
• Data set open contention related to PCLOSET being too small can cause time that is not accounted.
• Time for RMF interval data set statistics gathering can cause not accounted time.

DB2 internal suspend and resume can cause this not accounted time by looping when several threads are waiting for the same resource, but this case is very rare.