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diff --git a/source/concepts/janitor.rst b/source/concepts/janitor.rst new file mode 100644 index 0000000..52765ed --- /dev/null +++ b/source/concepts/janitor.rst @@ -0,0 +1,41 @@ +The Janitor Process +=================== +The janitor process carries out periodic cleanup tasks. For example, +it is used by +:doc:`omfile <../configuration/modules/omfile>` +to close files after a timeout has expired. + +The janitor runs periodically. As such, all tasks carried out via the +janitor will be activated based on the interval at which it runs. This +means that all janitor-related times set are approximate and should be +considered as "no earlier than" (NET). If, for example, you set a timeout +to 5 minutes and the janitor is run in 10-minute intervals, the timeout +may actually happen after 5 minutes, but it may also take up to 20 +minutes for it to be detected. + +In general (see note about HUP below), janitor based activities scheduled +to occur after *n* minutes will occur after *n* and *(n + 2\*janitorInterval)* +minutes. + +To reduce the potential delay caused by janitor invocation, +:ref:`the interval at which the janitor runs can be be adjusted <global_janitorInterval>`\ . +If high precision is +required, it should be set to one minute. Janitor-based activities will +still be NET times, but the time frame will be much smaller. In the +example with the file timeout, it would be between 5 and 6 minutes if the +janitor is run at a one-minute interval. + +Note that the more frequent the janitor is run, the more frequent the +system needs to wakeup from potential low power state. This is no issue +for data center machines (which usually always run at full speed), but it +may be an issue for power-constrained environments like notebooks. For +such systems, a higher janitor interval may make sense. + +As a special case, sending a HUP signal to rsyslog also activate the +janitor process. This can lead to too-frequent wakeups of janitor-related +services. However, we don't expect this to cause any issues. If it does, +it could be solved by creating a separate thread for the janitor. But as +this takes up some system resources and is not not considered useful, we +have not implemented it that way. If the HUP/janitor interaction causes +problems, let the rsyslog team know and we can change the implementation. + |