Tasks perform the activities that are requested by users of the database session or by the kernel.
The following table lists the most important tasks.
Tasks
Name |
Description |
Event task |
The event task accepts events that are created in the kernel and communicates them externally. |
Log writer |
The log writers write log entries from the log wait queue to the log area, for example after a COMMIT or at a savepoint. |
Pager (data writer) |
Pagers write the data from the data cache to the data volumes at each savepoint. With a large data cache, it can take a very long time to perform a savepoint, which is why the pagers in this case become active between the end of a savepoint and the start of the next savepoint as well, in order to asynchronously save the data that has changed asynchronously. During a restart, the pagers read the converter pages from the data volumes into the converter. The number of pagers required is calculated by the system itself. It is primarily dependent on the size of the data cache and the number of data volumes. |
Server task |
The server tasks parallelize database functions. They are required for example to back up data and log entries, create indices and to finally delete tables. During a restart, they import log entries and process transactions in parallel. You can configure the number of server tasks that are available using the MAXSERVERTASKS special database parameter. |
Timer task |
The timer task is responsible for timeouts of SQL lock requests and checks whether log entries can be backed up. |
Trace writer task |
The trace writer task writes the trace entries in the main memory when the database trace is switched on. |
User task |
User tasks are responsible for processing statements from users. When a database session is opened, exactly one user task is assigned to each user. You can configure the number of user tasks that are available using the MAXUSERTASKS special database parameter. |
Utility task |
The utility task performs administration tasks. |
See also:
Threads and Tasks of a Database Instance