In SS sweep blocks establishment of concurrent attachments [CORE4135] #4462
Commented by: @hvlad
Before the fix the order of events when attachment is established was :
TRA_sweep is run while exclusive access to dbb is holds, therefore it blocks cuncurrent attach_database calls.
New order of events is:
If exception is raised after "ATTACH_DATABASE" was fired, then "ERROR" and "DETACH_DATABASE" events will be fired.