You can limit the number of results returned when you search for users and groups and set a user directory timeout for vCenter Server.
vCenter Server systems that use a directory service regularly validate users and groups against the user directory domain. Validation occurs at regular intervals specified in the vCenter Server settings. For example, if user Smith was assigned permissions and in the domain the user’s name was changed to Smith2, the host concludes that Smith no longer exists and removes permissions for that user when the next validation occurs.
Similarly, if user Smith is removed from the domain, all permissions are removed when the next validation occurs. If a new user Smith is added to the domain before the next validation occurs, the new user Smith receives all the permissions the old user Smith was assigned.