Bugzilla

(In reply to Richard Leger from comment #70)
> The point of this bug is not so much about using or not using offline support, but rather the slow speed of Thunderbird to load caldav calendar with thousand of items, as it happens every time you start TB with or without offline support and the **high number of network requests** and the **lengthy time** required to for response parsing/ui populating. While calendar perf has improved over the past year, it still not great in regards to this bug.

Thanks a lot for this clarification. By the way, my impression is that old versions were faster in this behaviour. Unfortunately, I can no longer measure this, my order of magnitude is just the frustration or the number of complaints from our employees. The combination of both bugs (high number of network requests and missing events in offline support) we advise people to subscribe the personal calendar without offline support, the rest with offline support and deactivate all those regularly.
  
> @benedikt.kaless what do you mean by "slowness"? Is it at startup? Or afterwards during TB usage?

I describe "slowness" as following: When people subscribe to more than 10 calendars thunderbird needs up to 3-5 minutes after start before it is usuable. During startup it doesn't react on mouse-clicks and doesn't load new mails. But furthermore, it responds slowly even after hours of use. For example, characters are displayed with such a delay when composing emails that entire sentences get mixed up when typing. Colleagues pre-formulate emails in text editors and copy and paste them. It's a frustrating user experience :)
On my Linux I get a warning ‘Thunderbird is not responding’ at regular intervals

> It is quite impressive that you can use  5-10 calendars at a time, as not long ago that would crawl TB or make it unresponsive for minutes or bring it in an unusable state. 

My impression is, it depends on the amount of events in these calendars and how often they change of course.

> (In reply to benedikt.kaless from comment #68)
> > Due to this bug 1694709 offline-support is not activated for all those calendars because events are vanishing in a calendar using offline support.
> 
> I can confirm as well, though I haven't yet noticed recently in TB 128.3.1, it is too early to tell as it happens randomly. A way to fix it is do disable offline support, and re-enable it, so missing items re-appear as the full calendar is reloaded in cache. The main problem being that event disappearing/missing are not necessarily noticed by end-users as it happens silently, so it causes them to miss meetings double book them, etc... That also the reason we disabled offline support for network calendars in organisations we support as online calendar is the most reliable. Not the point of this bug but good to be aware of :-)

This bug unfortunately leaves users with the impression that they cannot rely on Thunderbird as a tool in their day-to-day work. If appointments are missing, they are not reminded of meetings and miss them. 

The combination of both bugs is really critical for users because it means that workflows that you simply need in everyday office life don't work.
Perhaps - I am not familiar with the codebase of thunderbird - it is a quick win to don't sync hidden calendars. People are used to hide calendars via the "eye"-symbol and show calendars as soon as they want to coordinate meetings.

I think it's good that there's movement in this thread again. I can only expressly ask you to deal with this behaviour, because it's a real blocker right now.

Thanks
Benedikt