Kill user sessions dynamically through PL/SQL

Question

Hello,
Every night I have to DROP one user in order to recreate the entire schema. In order to do this I have to disconnect the user from the DB by killing its sessions. I am using following PL/SQL code
ALTER SYSTEM ENABLE RESTRICTED SESSION;
begin
    for x in (
            select Sid, Serial#, machine, program
            from v\$session
       where username = 'STARSTAGING_DB'
   ) loop
          execute immediate 'Alter System DISCONNECT Session '''|| x.Sid
                  || ',' || x.Serial# || ''' IMMEDIATE';
    end loop;
end;
DROP USER starstaging_db CASCADE;
ALTER SYSTEM DISABLE RESTRICTED SESSION;
I have also tried using keyword KILL instead of DISCONNECT of session.
Most of the day this works, user is dropped and new one is created, but sometimes I get the following problem.
The problem that has occurred in a log file is:
PL/SQL procedure successfully completed.
DROP USER starstaging_db CASCADE
ERROR at line 1:
ORA-01940: cannot drop a user that is currently connected
System altered.
CREATE USER STARSTAGING_DB IDENTIFIED BY *****
ERROR at line 1:
ORA-01920: user name 'STARSTAGING_DB' conflicts with another user or role name
Does anyone have an idea how I can make sure that the user for sure disconnects, so that I can drop him?
Best Regards,
Vladimir

Answer 1

Cannot comment on a better approach as that means a proper analysis of the business requirements. Just keep in mind that killing sessions is a brutal way to manage user connectivity to the database - and should be seen as an exception and the last resort.
You can wrap your schema drop code into a retry loop. Something as follows:
loop
   begin
      ..do the drop..
      success := true;
  exception when FAILED then
      dbms_lock.sleep(60); -- sleep 60 seconds
  end;
  retry := retry + 1;
  exit when success or retry > HAVE_WAITED_LONG_ENOUGH;
end loop;