[5.0] Enable the system plugin on upgrade

[laoneo]

Summary of Changes

Since some system plugin code is moved to tasks, the scheduler system plugin should be activate on update. When it is disabled, then we can run into the issue that the session table doesn't get cleaned up. We all know what the consequences are.

A reason to disable the system plugin is when sites are using the crontab feature of linux as it is more reliable that the lazy scheduler plugin.

This needs to be documented on docs.joomla.org. Any help would be appreciated for the documentation taskas it affects every site with a disabled scheduler system plugin.

Testing Instructions

• Disable the system scheduler plugin on 4.x
• Update to 5.0

Actual result BEFORE applying this Pull Request

Scheduler plugin is not activated.

Expected result AFTER applying this Pull Request

Scheduler plugin is activated.

Link to documentations

Please select:

• Documentation link for docs.joomla.org:

• No documentation changes for docs.joomla.org needed

• Pull Request link for manual.joomla.org:

• No documentation changes for manual.joomla.org needed

[laoneo]

Marking it as release blocker.

[richard67]

We need this plugin enabled only if there is no cli cron or webcron triggering the scheduler, is that right? If yes: Is there a way to determine if there is such an external trigger, e.g. a check when the scheduler has been triggered last time and a reasonable assumption how long that can be ago to know we have no external trigger?

[laoneo]

I don't know exactly and have no time to do further investigation. All I know is that at least the session gc task must run periodically. So this here is the safest option. If you want to do some more enhanced checks, go for it.

[richard67]

I don't know exactly and have no time to do further investigation. All I know is that at least the session gc task must run periodically. So this here is the safest option. If you want to do some more enhanced checks, go for it.

@laoneo Well, I think more enhanced checks might be possible but would be overkill. But maybe a postinstall message would make sense which notifies about the plugin being enabled with the update and in which case they might want to disable it? @HLeithner What do you think?

[HLeithner]

yes postinstallation message would make sense, at least for upgrades.

[HLeithner]

can we get a manual entry please