oracle--select for update nowait 与 select for update 区别
nowait的含义很多人都会误解为“不用等待，立即执行”。但实际上该关键字的含义是“不用等待，立即返回”
如果当前请求的资源被其他会话锁定时，会发生阻塞，nowait可以避免这一阻塞，因为
If another user is in the process of modifying that row, we will get an ORA‐00054Resource Busy error. We are blocked and must wait for the other user to finish withit.可以实验下，我用pl/sql developer锁定表game
SQL> select * from game where game_id=1 for update nowait;select * from game where game_id=1 for update nowait*
SQL> select lo.oracle_username,do.object_name,s.logon_time,lo.process,s.sid as session_id 2 from v$locked_object lo,v$session s,dba_objects do 3 where lo.session_id = s.sid and do.object_id = lo.OBJECT_ID 4 /ORACLE_USERNAME------------------------------OBJECT_NAME--------------------------------------------LOGON_TIME PROCESS SESSION_ID------------------- ------------ ----------NBA---用户名称GAME---操作的对象2009-08-04 10:55:15---登录的时间 840:5176 10
selectsql_textfromv$session a,v$sqltext_with_newlines bwhereDECODE(a.sql_hash_value,0, prev_hash_value, sql_hash_value)=b.hash_value anda.sid=10;begin :id := sys.dbms_transaction.local_transaction_id; end;kill sessionSQL> select sid,serial# from v$session where sid =10; SID SERIAL#---------- ---------- 10 23SQL> alter system kill session '10,23';
