几个惯用的数据库操作以及视图
一.查看表空间剩余百分比
SELECT tablespace_name, TO_CHAR
(100*sum_free_blocks/sum_alloc_blocks, '999.99')
AS percent_free
FROM
(SELECT tablespace_name, SUM(blocks)
AS sum_alloc_blocks
FROM dba_data_files
GROUP BY tablespace_name),
(SELECT tablespace_name
AS fs_ts_name,MAX(blocks)
AS max_blocks,
COUNT(blocks)
AS count_blocks, SUM(blocks) AS sum_free_blocks
FROM dba_free_space
GROUP BY tablespace_name)
WHERE tablespace_name = fs_ts_name
ORDER BY percent_free DESC;
涉及的视图有：dba_free_space dba_data_files
二.查看当前sessions的sid,pid,以及serial#等
select p.pid, p.spid, s.sid, s.serial# from v$session s,v$process p
where s.sid = (select sid from v$mystat where rownum = 1) and p.addr = s.paddr
涉及的视图有：v$session v$process v$mystat
三.查看回滚段与数据段信息的一些SQL
1.系统实际UNDO表空间占用率可以使用如下语句来计算。
select ((select (nvl(sum(bytes),0)) from dba_undo_extents where tablespace_name ='UNDOTBS1' and status in ('ACTIVE','UNEXPIRED')) *100) / (select sum(bytes) from dba_data_files where tablespace_name='UNDOTBS1') "PCT_INUSE" from dual;
PCT_INUSE
----------
27.575
将UNEXPIRED，ACTIVE两种状态的回滚段一起算上，实际现场的UNDO占用率为27.575%。
2.查看表空间的使用情况
SELECT A.TABLESPACE_NAME,A.BYTES/1024/1024 TOTAL,B.BYTES/1024/1024 USED, C.BYTES/1024/1024 FREE,
(B.BYTES*100)/A.BYTES "% USED",(C.BYTES*100)/A.BYTES "% FREE"
FROM SYS.SM$TS_AVAIL A,SYS.SM$TS_USED B,SYS.SM$TS_FREE C
WHERE A.TABLESPACE_NAME=B.TABLESPACE_NAME AND A.TABLESPACE_NAME=C.TABLESPACE_NAME;
3.查看回滚段的状况
select rownum, sys.dba_rollback_segs.segment_name Name, v$rollstat.extents
Extents, v$rollstat.rssize Size_in_Bytes, v$rollstat.xacts XActs,
v$rollstat.gets Gets, v$rollstat.waits Waits, v$rollstat.writes Writes,
sys.dba_rollback_segs.status status
from v$rollstat, sys.dba_rollback_segs, v$rollname
where v$rollname.name(+) = sys.dba_rollback_segs.segment_name and
v$rollstat.usn (+) = v$rollname.usn order by rownum;
4.查看数据段的信息
select * from dba_segments where tablespace_name ='UNDOTBS1'
相关视图：
select * from dba_rollback_segs
select * from v$rollstat
select * from v$rollname
select * from dba_undo_extents
select * from dba_segments where tablespace_name ='UNDOTBS1'
涉及的视图有：dba_rollback_segs v$rollstat v$rollname dba_undo_extents dba_segments
4.定位高耗资源的SQL
select sql_text,
sharable_mem,persistent_mem,runtime_mem,
sorts,
users_opening,
executions,
loads,
parse_calls,
disk_reads,buffer_gets,rows_processed,
optimizer_mode,address,hash_value
from v$sql
order by disk_reads desc;
根据上述语句的输出的sql_text定位执行对应sql的Oracle进程ID：
select a.sid,a.osuser "程序用户",a.process "程序ID",
a.username "ORA用户" ,a.terminal "P终端",
b.spid "后台ID",b.username "后台用户",
b.terminal "B终端"
from v$session a,v$process b
where a.paddr = b.addr and (a.sql_address,a.sql_hash_value) in (
select address,hash_value from v$sqltext where
upper(sql_text) like '%ZXDBM_ISMP.SYNC_TASK%'
)
'%ZXDBM_ISMP.SYNC_TASK%' 部分使用第一个sql查询出来的sql_text代替；
查询结果中的spid "后台ID" 就是执行该sql对应的oracle进程的pid(oracle服务器上的oracle进程)。如果确认高耗资源的sql可以中止执行以释放系统资源，需要在数据库服务器上使用oracle用户将查询出来的spid 杀掉（kill -9 spid）。如果高耗资源的sql执行了表的增、删、改操作，也需要kill掉对应的oracle后台进程以释放这些表的锁资源；
涉及的视图有：v$sql v$session v$process v$sqltext
五.修改数据库的连接数
修改Oracle数据库的连接数
1. 查看processes和sessions参数
SQL> show parameter processes
NAME TYPE VALUE
db_writer_processes integer 1
gcs_server_processes integer 0
job_queue_processes integer 10
log_archive_max_processes integer 2
processes integer 50
SQL> show parameter sessions
NAME TYPE VALUE
license_max_sessions integer 0
license_sessions_warning integer 0
logmnr_max_persistent_sessions integer 1
sessions integer 60
shared_server_sessions integer
2. 修改processes和sessions值
SQL> alter system set processes=300 scope=spfile;
系统已更改。
SQL> alter system set sessions=335 scope=spfile;
系统已更改。
3. 修改processes和sessions值必须重启oracle服务器才能生效
ORACLE的连接数(sessions)与其参数文件中的进程数(process)有关，它们的关系如下：
sessions=(1.1*process+5)
查询数据库当前进程的连接数：
select count(*) from v$process;
查看数据库当前会话的连接数：
select count(*) from v$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$parameter where name = 'processes';
或者：show parameter processes;
修改数据库允许的最大连接数：
alter system set processes = 300 scope = spfile;
(需要重启数据库才能实现连接数的修改)
重启数据库：
shutdown immediate;
startup;
查看当前有哪些用户正在使用数据：
select osuser,a.username,cpu_time/executions/1000000||'s',sql_fulltext,machine
from v$session a,v$sqlarea b
where a.sql_address = b.address
order by cpu_time/executions desc;
备注：UNIX 1个用户session对应一个操作系统process，而Windows体现在线程。
启动oracle
su - oracle
sqlplus system/pwd as sysdba //进入sql
startup //启动数据库
lsnrctl start //启动监听
sqlplus "/as sysdba"
shutdown immediate;
startup mount;
alter database open;
6.查询数据库对象锁定的情况
--查看某个表被谁锁定
select t2.username, t2.sid, t2.serial#, t2.logon_time, t3.object_name
from v$locked_object t1, v$session t2, dba_objects t3
where t1.session_id = t2.sid
and t1.object_id = t3.object_id
order by t2.logon_time;
--杀掉进程
alter system kill session 'sid,serial#'; ---sid,serial#对应上面语句查出的value
涉及的视图有：v$locked_object v$session dba_objects
锁的情况在测试环境中出现了很多次了，建议每次业务由通变成不通时，用这个SQL查看下是不是因为某个表被锁而导致的。