Special Thread
Special threads are operating system threads. They provide those services to user kernel threads that the user kernel threads must process asynchronously. Those services include connection requests, reading or writing to data volumes, and backups.
|
Name |
Description |
|---|---|
|
Coordinator |
The Coordinator thread monitors all threads in the database. It is the first thread that the system creates when the database is started. It coordinates the start processes of the other threads. If errors occur, the Coordinator thread can stop other threads. |
|
Requester |
The Requester thread accepts user logons to the database 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 on 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> ). The Dev thread dev0 plays a special role here. It coordinates and monitors the other Dev threads. The number of Dev threads is primarily dependent on the number of volumes in the database. 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 time-outs, for internal load balancing and for other time-dependent internal controls. |
|
Worker |
The Worker thread is responsible for reporting completed asynchronous I/O operations. |
Concepts of the Database System, Threads