查询当前数据库连接数，进程数，启动数据库
查询数据库当前进程的连接数：
select count(*) from v$process;
查看数据库当前会话的连接数：
elect count(*) from v$session;
查看数据库的并发连接数：
select count(*) from v$session where status=‘ACTIVE‘;
查看当前数据库建立的会话情况：
select sid,serial#,username,program,machine,status from v$session;
查询数据库允许的最大连接数：
select value from v$parameter where name = ‘processes‘;
或者：show parameter processes;
查询所有数据库的连接数
selectschemaname,count(*)fromv$sessiongroupbyschemaname;
查询终端用户使用数据库的连接情况。
selectosuser,schemaname,count(*)fromv$sessiongroupbyschemaname,osuser;
#查看当前不为空的连接
select * from v$session where username is not null
#查看不同用户的连接数
select username,count(username) from v$session where username is not null group by username
#连接数
select count(*) from v$session
#并发连接数
Select count(*) from v$session where status=‘ACTIVE‘
#最大连接
show parameter processes
#修改连接
alter system set processes = value scope = spfile
修改数据库允许的最大连接数：
alter system set processes = 300 scope = spfile;
(需要重启数据库才能实现连接数的修改)
重启数据库：
shutdown immediate;
startup;
查看当前有哪些用户正在使用数据：
select osuser,a.username,cpu_time/executions/1000000||‘s‘,sql_fulltext,machine
from v$session a,v$sqlarea b
where a.sql_address = b.address
order by cpu_time/executions desc;
备注：UNIX 1个用户session对应一个操作系统process，而Windows体现在线程。
oracle中查询被锁的表并释放session
SELECT A.OWNER,A.OBJECT_NAME,B.XIDUSN,B.XIDSLOT,B.XIDSQN,B.SESSION_ID,B.ORACLE_USERNAME, B.OS_USER_NAME,B.PROCESS, B.LOCKED_MODE, C.MACHINE,C.STATUS,C.SERVER,C.SID,C.SERIAL#,C.PROGRAM
FROM ALL_OBJECTS A,V$LOCKED_OBJECT B,SYS.GV_$SESSION C
WHERE ( A.OBJECT_ID = B.OBJECT_ID ) AND (B.PROCESS = C.PROCESS ) ORDER BY 1,2
释放session Sql:
alter system kill session ‘sid, serial#‘
alter system kill session ‘379, 21132‘
alter system kill session ‘374, 6938‘
查看占用系统io较大的session
SELECT se.sid,se.serial#,pr.SPID,se.username,se.status,se.terminal,se.program,se.MODULE,se.sql_address,st.event,st.p1text,si.physical_reads,si.block_changes
FROM v$session se, v$session_wait st,v$sess_io si,v$process pr
WHERE st.sid=se.sid AND st.sid=si.sid AND se.PADDR=pr.ADDR AND se.sid>6 AND st.wait_time=0 AND st.event NOT LIKE ‘%SQL%‘ ORDER BY physical_reads DESC
找出耗cpu较多的session
select a.sid,spid,status,substr(a.program,1,40) prog,a.terminal,osuser,value/60/100 value
from v$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
查询session被锁的sql可以用一下语句
select sys.v_$session.osuser,sys.v_$session.machine,v$lock.sid,
sys.v_$session.serial#,
decode(v$lock.type,
‘MR‘, ‘Media Recovery‘,
‘RT‘,‘Redo Thread‘,
‘UN‘,‘User Name‘,
‘TX‘, ‘Transaction‘,
‘TM‘, ‘DML‘,
‘UL‘, ‘PL/SQL User Lock‘,
‘DX‘, ‘Distributed Xaction‘,
‘CF‘, ‘Control File‘,
‘IS‘, ‘Instance State‘,
‘FS‘, ‘File Set‘,
‘IR‘, ‘Instance Recovery‘,
‘ST‘, ‘Disk Space Transaction‘,
‘TS‘, ‘Temp Segment‘,
‘IV‘, ‘Library Cache Invalida-tion‘,
‘LS‘, ‘Log Start or Switch‘,
‘RW‘, ‘Row Wait‘,
‘SQ‘, ‘Sequence Number‘,
‘TE‘, ‘Extend Table‘,
‘TT‘, ‘Temp Table‘,
‘Unknown‘) LockType,
rtrim(object_type) || ‘ ‘ || rtrim(owner) || ‘.‘ || object_name object_name,
decode(lmode, 0, ‘None‘,
1, ‘Null‘,
2, ‘Row-S‘,
3, ‘Row-X‘,
4, ‘Share‘,
5, ‘S/Row-X‘,
6, ‘Exclusive‘, ‘Unknown‘) LockMode,
decode(request, 0, ‘None‘,
1, ‘Null‘,
2, ‘Row-S‘,
3, ‘Row-X‘,
4, ‘Share‘,
5, ‘S/Row-X‘,
6, ‘Exclusive‘, ‘Unknown‘) RequestMode,
ctime, block b
from v$lock, all_objects, sys.v_$session
where v$Lock.sid > 6
and sys.v_$session.sid = v$lock.sid
and v$lock.id1 = all_objects.object_id;
启动oracle
su - oracle
sqlplus system/pwd as sysdba //进入sql
startup //启动数据库
lsnrctl start //启动监听
sqlplus "/as sysdba"
shutdown immediate;
startup mount;
alter database open;