Overview of Special Threads

Use

Special threads provide services for the user kernel threads.

Overview of Special Threads

Name

Description

Coordinator

The coordinator thread monitors all threads in the database instance. It is the first thread that the database instance creates when it is started and coordinates the start operations of the other threads. If an error occurs, the coordinator thread can stop other threads.

Requester

The requester thread accepts user logons to the database instance and assigns them to a user task within a user kernel thread.

Console

The console thread processes the requests of the XCONS database tool (database console).

Clock

Only for Microsoft Windows

The clock thread sets a global time variable with which internal time measurements are aligned.

dev<n>

Dev threads are responsible for carrying out write and read requests of the tasks in the volumes.

The dev threads are numbered sequentially (dev<n>). Dev thread dev0 has a special role: it coordinates and monitors the other dev threads.

The number of dev threads is primarily dependent on the number of volumes in the database instance. The database system activates two dev threads for each data volume and each log volume. If the database trace is on, the database system activates a dev thread for it as well.

asdev<i>

To perform data backups, the database system activates temporary dev threads asdev<i> for reading and writing the data.

Timer

Timer threads are responsible for monitoring the time for timeouts, for internal load balancing and for other time-dependent internal controls.

Worker

The worker thread is responsible for reporting completed asynchronous I/O operations.

Activities

To display information about threads, use the Database Manager or XCONS or in SAP systems the database assistant or liveCache assistant. See

?     Database Manager GUI, Displaying Database Sessions

?     Database Manager CLI, show

?     XCONS documentation

?     Database Administration in CCMS: MaxDB, Kernel Threads

See also:

Process Structure