Oracle 会话并发问题

SELECT session_id  
        INTO v_session_id  
        FROM lf_session_log  
       WHERE (ROWID) IN (SELECT row_id  
                           FROM (SELECT ROWID row_id  
                                    FROM lf_session_log  
                                   WHERE query_state = 'R'  
                                         AND expdttime > sysdate  
                                         AND service_type = 1  
                                         AND session_type = 'P')  
                          WHERE rownum = 1)  
         FOR UPDATE wait 2;  
      
      UPDATE lf_session_log  
         SET query_state = 'U', expdttime = p_expdttime  
       WHERE session_id = v_session_id  
      RETURNING session_id INTO p_session_id;  
commit;  
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