Default service superclasses and subclasses
Each new or upgraded database has three predefined default service superclasses: the default user class, the default maintenance class, and the default system class.
The default service superclasses are created with one or more default service subclasses. You cannot create additional service subclasses for the default service superclasses, and you cannot disable or drop any of the default service superclasses. Default service superclasses and their default service subclasses are dropped only when the database is dropped.
All work that is issued by connections to a default service superclass is processed in the default service subclass of that service superclass.
- Default user service superclass (SYSDEFAULTUSERCLASS)
- By default, all user activities run in SYSDEFAULTUSERCLASS.
SYSDEFAULTUSERCLASS has two default service subclasses: SYSDEFAULTSUBCLASS and SYSDEFAULTMANAGEDSUBCLASS.
Heavyweight
queries run in SYSDEFAULTMANAGEDSUBCLASS, where they can be controlled and monitored as a group. For more information, see Default query concurrency management. - Default maintenance service superclass (SYSDEFAULTMAINTENANCECLASS)
- The default maintenance service superclass tracks the internal Db2® connections that
perform database maintenance and administration tasks. Connections from the Db2 asynchronous
background processing (ABP) agents are mapped to this service superclass. ABP agents are internal
agents that perform database maintenance tasks. Asynchronous index cleanup (AIC) is an example of an
ABP-driven task. ABP agents automatically reduce their resource consumption and number of subagents
when the number of user connections increases on the data server. Utilities that are issued by user
connections are mapped using regular service classes. You cannot implement service class thresholds
on SYSDEFAULTMAINTENANCECLASS.
The default service subclass for SYSDEFAULTMAINTENANCECLASS is always created with the name SYSDEFAULTSUBCLASS.
The internal connections that are tracked by the default maintenance service superclass include:- ABP connections (including AIC)
- Health monitor initiated backup
- Health monitor initiated RUNSTATS
- Health monitor initiated REORG
- Default system service superclass (SYSDEFAULTSYSTEMCLASS)
- The default system service superclass tracks internal Db2 connections and
threads that perform system-level tasks. You cannot define service subclasses for this service
superclass, nor can you associate any workloads or work actions with it. In addition, you cannot
implement service class thresholds on SYSDEFAULTSYSTEMCLASS.
The default service subclass for SYSDEFAULTSYSTEMCLASS is always created with the name SYSDEFAULTSUBCLASS.
The Db2 threads and connections that are tracked by the default system service superclass include:- ABP daemon (db2taskd)
- Self-tuning memory manager (db2stmm)
- Prefetcher engine dispatchable units (EDUs) (db2pfchr)
- Page cleaner EDUs (db2pclnr)
- Log reader EDUs (db2loggr)
- Log writer EDUs (db2loggw)
- Log file reader EDUs (db2lfr)
- Deadlock detector EDUs (db2dlock)
- Event monitors (db2evm)
- Event monitor fast writers (db2fw)
- Last used daemon (db2lused)
- Package cache daemon (db2pcsd)
- Connections performing system-level tasks