Bug 441906

SUMMARY

When an application sends hundreds of notifications in short succession, the system may freeze (out of memory?). 
This is often caused by a reconnecting to the internet after e.g. having been on stand-by, and receiving notifications for each and every missed chat message at once.


STEPS TO REPRODUCE
1. Run a program which creates a notification on e.g. an incoming chat message (for instance, Telegram or Discord).
2. Go 'offline' for some time. I commonly trigger it because my computer was on  'stand by' for a couple of hours and then wakes up again.
3. On reconnecting to the internet, hundreds of messages appear in close succession.
4. The notification manager tries to create and display a notification window for all of these.

OBSERVED RESULT

In the best case, multiple minutes where the rightmost part of the screen is covered by a super high stack of notifications which are appearing and disappearing in rapid succession, often with a slowdown of the machine as a whole (as significant effort seems to be put in creating/animating all of these notifications).

In the worst case, the computer hangs with a frozen screen, requiring a hard-reset restart. My assumption is that this happens because so many notifications are created that the computer runs out of RAM.

EXPECTED RESULT
It is expected that all notifications will show up in the 'history' tab of the notification manager, but it does not make sense to pop-up all of them. Maybe a rate-limiting technique can be used to limit excessive notification requests. For instance, limit pop-up to a maximum of, five per application per second.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Manjaro 21.1.1
(available in About System)
KDE Plasma Version: 5.22.4
KDE Frameworks Version: 5.85.0
Qt Version: 5.15.2