今天新装一个库，最后dbconsole起不来，最后想用emca -repos recreate重建一个EM资料库
重建EM资料库会先删后建，删的时候，会启动数据库到quiesce模式，这个一定要注意

删的时候，很久都没动静，v$session_wait看到是经常在latch: library cache上等待，很奇怪
捕获SQL看了下
declare
  l_username varchar2(30);
  l_sid number;
  l_serial number;
  err number;
  c number;
begin
    -- Now, drop the SYSMAN user
    c := 0;
    l_username := upper('SYSMAN');
    begin
     loop
        BEGIN
          LOOP
            BEGIN
              FOR crec in (SELECT sid, serial#
                             FROM v$session
                    WHERE upper(username)=l_username
                              AND status NOT IN('KILLED'))
              LOOP
                BEGIN
                   EXECUTE IMMEDIATE 'ALTER SYSTEM KILL SESSION ''' ||
                                     crec.sid || ',' || crec.serial# || '''';
                  EXCEPTION
                      WHEN OTHERS THEN
                         err := SQLCODE;
                         IF err != -30 THEN
                            EXIT;
                         END IF;
                END;
                commit;
              END LOOP;
              EXCEPTION
                WHEN OTHERS THEN
                  err := SQLCODE;
                  IF err != -30 THEN
                    EXIT;
                  END IF;
            END;
            IF SQL%NOTFOUND THEN
               EXIT;
            END IF;
            commit;
          END LOOP;
          execute immediate 'drop user ' || l_username || ' cascade';
          exit;
          EXCEPTION
            WHEN NO_DATA_FOUND THEN
              exit;
            WHEN OTHERS THEN
              err := SQLCODE;
              IF err = -1918 THEN
                EXIT;
              ELSE
                IF err = -1940 THEN
                   NULL;
                ELSE
                   DBMS_OUTPUT.PUT_LINE('not 1940 err' || err);
                   c := c+1;
                   IF c > 50 THEN
                      RAISE;
                   END IF;
                END IF;
              END IF;
        END;
      end loop;
    end;
    commit;

end;

这个SQL不停的出现，是在做一个轮询，估计是卡在哪里了
判断这个SESSION的逻辑，其是在杀dbsnmp用户，检查了下dbsnmp，发现有2个KILL状态的dbsnmp用户的SESSION。
在OS上干掉，OK。

另外说下resmgr:become active这个Scheduler类的等待，应该是由于数据库在quiesce模式，其他非SYSDBA权限的SESSION等待