I inserted some data my means of SQL into a SDE managed table - or to be more precise into the SDE managed view belonging to the table.
I had done that before and so far it had worked without any issues. This time the compress operation didnt compress at least the table I had inserted rows. I ran compress a few times but to no avail. I restarted ArcGIS server but again it didnt change the result. Then I stopped ArcGIS server and killed all remaining connections to the Oracle schema and ran compress again. This time compress finished succesfully. Up to now I never had to kill all connections - so I assume there was something different this time.
ArcMap 10.5.1, Oracle 11.2.0.4
