Special threads provide services for the user kernel threads that have to be processed asynchronously from the user kernel threads’ point of view.
Special threads
Name |
Description |
Coordinator |
The coordinator thread monitors all threads in the database instance. It is the first thread that is created when the database instance is started and coordinates the start operations of the additional threads. If operating errors occur, 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 |
The clock thread sets a global time variable which serves as a reference for internal time measurements. It is only used in Microsoft Windows. |
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 initially depends on the number of volumes in the database instance. Normally, two dev threads are activated for each data volume and each log volume; a dev thread is also activated, if it is switched on, for writing the database trace. |
asdev<i> |
To perform data backups, temporary dev threads asdev<i> are activated for reading and writing the data. |
Timer |
Timer threads are responsible for monitoring the time with regard to timeouts and for other time-dependent internal controls. |
Worker |
The worker thread is responsible for reporting completed asynchronous I/O operations. |