Note: some of the contents in this wiki come from the article here - thanks go to Mitchel Sellers.

DotNetNuke.Entities.Users.PurgeUsersOnline (friendly name of "Purge Users online")

This task is one that is used by the Users Online module within DNN. When this task executes it will remove users from the listing of online users that are no longer active in your site. When using this module the time frequency for this module is something that you want to take into careful consideration, more details will be discussed in the "When to change" section

Standard Schedule

By default this task is NOT ENABLED by DNN, if you enable users online it will execute every 1 minute to purge the users

When to Change

Typically the default values for this functionality is ok if you are using the module, if you run an incredibly high activity site though you might consider adjusting this to run every 5 minutes or so, just to reduce the minimal load that it does add to your site

DotNetNuke.Services.Log.SiteLog.PurgeSiteLog (friendly name of "Purge site log")

This task if it is enabled will purge the records in the site log that are older than the specified history time. This task is highly important as when using the site log this will prevent the log table from growing too large

Standard Schedule

By default this task is NOT ENABLED by DNN, if you enable this task the default run frequency is once per day.

When to Change

This task is one that by the nature of how it works is best to leave at a 1 per day schedule as it only cleans records based on a daily basis

DotNetNuke.Services.Scheduling.PurgeScheduleHistory (friendly name of "Purge Schedule History")

This task is used to purge records from the Schedule History table. This is an important task because if your schedule history is left alone it is very possible for your database size to grow in a very rapid manner due to the sheer number of items that are completed by the scheduler.

Standard Schedule

By default this task is ENABLED by DNN and will execute once per day.

When to Change

This is another task that due to the nature of the action it performs changes to the schedule are not needed

DotNetNuke.Services.Log.EventLog.PurgeLogBuffer (friendly name of "Purge Log buffer")

This task is used to purge records from the Event Log queue to the database. This is an important feature of DNN as this task is what ensures that all actions are successfully recorded to the EventLog table.

Standard Schedule

By default this task is ENABLED by DNN and will execute once per minute

When to Change

You can modify this task to run less frequently on a highly active site and it might have minimal performance modifications. For example if it runs every minute and takes 5 seconds, you could schedule it to run every 5 minutes and it would take 25 seconds. However, in my experience with DotNetNuke it is not ever necessary to modify this task.

DotNetNuke.Services.Log.EventLog.SendLogNotifications (friendly name of "Send Log Notications")

This task is responsible for sending e-mail notifications to the administrator from the event log system.

Standard Schedule

By default this task is NOT ENABLED by DNN, if enabled it will execute once every 5 minutes by default.

When to Change

Due to the nature of urgent updates to the administrator, if this task is enabled I would not recommend changing the interval.

DotNetNuke.Services.Search.SearchEngineScheduler (friendly name of "Search Site Crawler")

This task is responsible for the population of the search engine within DNN. In older releases (pre DNN 7.1.0) when this task is executed all modules that support ISearchable will be polled for index information and if any exists it will be added to the database search index. In DNN 7.1.0 and above this release now looks for ModuleSearchBase and is able to request only changes of data from the last time the check was made (which performs much better). In addition, it supports other indexers such as a user-indexer, all of which only return changed data since the previous search. DNN 7.1.0 and above use a Lucene based search.

Standard Schedule

By default this task is ENABLED by DNN and will execute once every 30 minutes

When to Change

As mentioned earlier pre DNN 7.1.0 sites used an ineffiecent search so if using one of those releases you might consider changing this value to reduce performance overhead. For DNN 7.1.0 and above no such change should be necessary

DotNetNuke.Modules.Admin.ResourceInstaller.InstallResources

This task is responsible for the automatic installation of modules that have been placed in the various /Install folders in your DNN installation. This is a legacy scheduled task which has been removed from recent DNN versions (around the 6.x timeframe AFAIK)

Standard Schedule

By default this task is NOT ENABLED by DNN, if enabled it will execute once every 30 minutes by default.

When to Change

You can enable this task if you want to automatically install modules, however, I personally recommend NOT using this feature

DotNetNuke.Services.FileSystem.SynchronizeFileSystem

This task is responsible for updating the File Manager by syncronizing the DNN file system with your physical file system. This is needed if you add many files to your site via FTP and not using one of the "DNN ways" of uploading. This is a legacy scheduled task which has been removed from DNN since 6.0.

Standard Schedule

By default this task is NOT ENABLED by DNN, if enabled it will execute once every hour by default.

When to Change

If you use FTP to upload files to your /Portals/ folder you might enable this option, however, I personally recommend just using the "Recursive" sync option within file manager whenever I have an issue. My reasons for this are that if you have a large number of files, this task can take a very long time to execute.

DotNetNuke.Services.Cache.PurgeCache (friendly name of "Purge Module Cache")

This scheduled task is responsible for purging cache files from the hard drive when using the "Disk" method of caching. If you are using the "Disk" caching method this is a key scheduled task.

Standard Schedule

By default this task is ENABLED by DotNetNuke and will execute once per 2 hours.

When to Change

You can disable this task if you are working with "Memory" caching (which I highly recommend).
- See more at: http://mitchelsellers.com/blogs/2008/02/13/dotnetnuke-scheduler-explained.aspx#sthash.PsQkupiR.dpuf

DotNetNuke.Services.Social.Messaging.Scheduler.CoreMessagingScheduler (friendly name of "Messaging Dispatch")

This task is responsible for sending out any queued emails -this is needed as some tasks such as messaging roles/social groups can result in many emails and this could cause a page to operate slowly, or an email server to mistakenly think spam was being sent. Instead this task sends batches of emails (50 at a time) until the queue is finished.

Standard Schedule

By default this task is ENABLED by DNN and runs every minute.

When to Change

If your site has little email you might consider changing it to a longer frequency.