关于Oracle的session
1.如何查看session级的等待事件？
当我们对数据库的性能进行调整时，一个最重要的参考指标就是系统等待事件。$system_event,v$session_event,v$session_wait这三个视图里记录的就是系统级和session级的等待事件，通过查询这些视图你可以发现数据库的一些操作到底在等待什么？是磁盘I/O，缓冲区忙，还是插锁等等。
通过如下sql你可以查询你的每个应用程序到底在等待什么，从而针对这些信息对数据库的性能进行调整。
Select s.username,s.program,s.status,se.event,se.total_waits,se.total_timeouts,se.time_waited,se.average_wait
from v$session s, v$session_event se
Where s.sid=se.sid And se.event not like 'SQl*Net%' And s.status ='ACTIVE' And s.username is not null
2.oracle中查询被锁的表并释放session
SELECT A.OWNER,A.OBJECT_NAME,B.XIDUSN,B.XIDSLOT,B.XIDSQN,B.SESSION_ID,B.ORACLE_USERNAME, B.OS_USER_NAME,B.PROCESS, B.LOCKED_MODE, C.MACHINE,C.STATUS,C.SERVER,C.SID,C.SERIAL#,C.PROGRAM
from ALL_OBJECTS A,V$LOCKED_OBJECT B,SYS.GV_$SESSION C
WHERE ( A.OBJECT_ID = B.OBJECT_ID ) AND (B.PROCESS = C.PROCESS ) ORDER BY 1,2
释放session Sql:
alter system kill session 'sid, serial#'
alter system kill session '379, 21132'
alter system kill session '374, 6938'
3.查看占用系统io较大的session
SELECT se.sid,se.serial#,pr.SPID,se.username,se.status,se.terminal,se.program,se.MODULE,se.sql_address,st.event,st.p1text,si.physical_reads,si.block_changes
from v$session se, v$session_wait st,v$sess_io si,v$process pr
WHERE st.sid=se.sid AND st.sid=si.sid AND se.PADDR=pr.ADDR AND se.sid>6 AND st.wait_time=0 AND st.event NOT LIKE '%SQL%' ORDER BY physical_reads DESC
4.找出耗cpu较多的session
select a.sid,spid,status,substr(a.program,1,40) prog,a.terminal,osuser,value/60/100 value
from v$session a,v$process b,v$sesstat c
where c.statistic#=12 and c.sid=a.sid and a.paddr=b.addr order by value desc
5.查询session被锁的sql可以用一下语句
