In 800xA FP4, event list problem
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For integrity reasons, there exists no mechanism to delete events.
Think about what you could do then to audit lists... I believe some approvals ABB's System 800xA have in Food and Drug, Pharma, etc. businesses could be endagered if it was possible to manipulate with events.
By cold starting the Event Storage service all events are deleted.
To cold start, disable the Event Storage service (all service providers in parallel), erase (actually I suggest rename) the \\OperateITData\EventStorage folder on all aspect server nodes, then enable the Event Storage service again.
Once the operation is to be considered final, delete the old data folders.