Debugging slow thunderbird – calendar issues with deleted.sqlite

Thunderbird reacted sluggish. To debug, I did this:

  • in taskmanager looked up the PID of the thunderbird.exe process
  • started up procmon64.exe from the sysinternals suite (, now Micro$oft)
  • Updated the filter (6. icon on top, the blue-ish thing and then triangle) to „PID“ „is“ <enter the PID from taskmanager> then „Include“ and hit „Add“
  • Hit „Apply“ or „OK“ below the filter entries
  • In the events window lots of entries regarding „calendar-data\deleted.sqlite“, „calendar-data\cache.sqlite“, „calendar-data\cache.sqlite-shm“, „calendar-data\cache.sqlite-wal“ were shown. Thunderbird spent quite a lot of time looking at those kilobyte-sized files.

Solution was to disable „offline-support“ in the calendar entries: In thunderbird, open the calendar tab. On the lefthand side are the calendar providers. Right-click each of them and select properties (last entry). In the new window disable „offline-support“.

After that, stop thunderbird, wait 15-20 seconds (so that thunderbird can close itself properly) and try again.

It worked in my case – otherwise look in sysinternals process monitor again.