504 Accepting a recurring event with many attendes

[chibenwa]

GIVEN a recurring event with many attendee and exceptions
As an attentee (event had been ITIPed)
WHEN I accept it
Then the server timeouts

THis is performance related: less attendee / exceptions and it runs smooth (if exec time of ~1 minute means smooth)

I presume we sequentially try to update all attendance of all users which indeed runs f***ing slow