Oracle学习之路【四】DBA常用语句

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--查看表锁 
select * from sys.v_$sqlarea where disk_reads>100

--监控事例的等待 
select event,sum(decode(wait_Time,0,0,1)) "Prev", 
sum(decode(wait_Time,0,1,0)) "Curr",count(*) "Tot" 
from v$session_Wait 
group by event order by 4 

--回滚段的争用情况
select name, waits, gets, waits/gets "Ratio" 
from v$rollstat a, v$rollname b 
where a.usn = b.usn

--查看前台正在发出的SQL语句
select user_name,sql_text
　　 from v$open_cursor
　　 where sid in (select sid from (select sid,serial#,username,program
　　 from v$session
　　 where status='ACTIVE'))

--数据表占用空间大小情况
select segment_name,tablespace_name,bytes,blocks 
from user_segments 
where segment_type='TABLE' 
ORDER BY bytes DESC ,blocks DESC

--查看表空间碎片大小
    select tablespace_name,round(sqrt(max(blocks)/sum(blocks))*
           (100/sqrt(sqrt(count(blocks)))),2) FSFI
    from dba_free_space
    group by tablespace_name order by 1
    
--查看表空间占用磁盘情况
     select 
             b.file_id                                 文件ID号,
             b.tablespace_name                         表空间名,
             b.bytes                                 字节数,
             (b.bytes-sum(nvl(a.bytes,0)))                 已使用,
             sum(nvl(a.bytes,0))                         剩余空间,
             sum(nvl(a.bytes,0))/(b.bytes)*100         剩余百分比 
             from dba_free_space a,dba_data_files b 
             where a.file_id=b.file_id 
             group by b.tablespace_name,b.file_id,b.bytes 
             order by b.file_id

--查看session使用回滚段
SELECT  r.name 回滚段名,
        s.sid,
        s.serial#,
        s.username 用户名,
        t.status,
        t.cr_get,
        t.phy_io,
        t.used_ublk,
        t.noundo,
        substr(s.program, 1, 78) 操作程序
FROM   sys.v_$session s,sys.v_$transaction t,sys.v_$rollname r
WHERE  t.addr = s.taddr and t.xidusn = r.usn
ORDER  BY t.cr_get,t.phy_io

--查看SGA区剩余可用内存
select name,
　　　　　　sgasize/1024/1024　　　　　　　　"Allocated(M)",
　　　　　　bytes/1024　　　　　　　　　　　 "自由空间(K)",
　　　　　　round(bytes/sgasize*100, 2)　　　"自由空间百分比(%)"
　　 from   (select sum(bytes) sgasize from sys.v_$sgastat) s, sys.v_$sgastat f
　　 where  f.name = 'free memory'

--监控表空间I/O比例
select df.tablespace_name name,df.file_name "file",f.phyrds pyr, 
       f.phyblkrd pbr,f.phywrts pyw, f.phyblkwrt pbw 
from v$filestat f, dba_data_files df 
where f.file# = df.file_id 
order by df.tablespace_name

--监控SGA命中率
select a.value + b.value "logical_reads", 
       c.value "phys_reads", 
       round(100 * ((a.value+b.value)-c.value) / (a.value+b.value)) "BUFFER HIT RATIO" 
from v$sysstat a, v$sysstat b, v$sysstat c 
where a.statistic# = 38 and 
      b.statistic# = 39 and 
      c.statistic# = 40 

--监控 SGA 中字典缓冲区的命中率
select parameter, gets,Getmisses , getmisses/(gets+getmisses)*100 "miss ratio", 
(1-(sum(getmisses)/ (sum(gets)+sum(getmisses))))*100 "Hit ratio" 
from v$rowcache 
where gets+getmisses <>0 
group by parameter, gets, getmisses 

--监控 SGA 中共享缓存区的命中率，应该小于1%
select sum(pins) "Total Pins", sum(reloads) "Total Reloads", 
sum(reloads)/sum(pins) *100 libcache 
from v$librarycache

--监控 SGA 中重做日志缓存区的命中率，应该小于1%
SELECT name, gets, misses, immediate_gets, immediate_misses, 
Decode(gets,0,0,misses/gets*100) ratio1, 
Decode(immediate_gets+immediate_misses,0,0, 
immediate_misses/(immediate_gets+immediate_misses)*100) ratio2 
FROM v$latch WHERE name IN ('redo allocation', 'redo copy')

--监控内存和硬盘的排序比率，最好使它小于 .10
SELECT name, value 
FROM v$sysstat 
WHERE name IN ('sorts (memory)', 'sorts (disk)') 

--监控字典缓冲区
SELECT SUM(GETS) "DICTIONARY GETS",SUM(GETMISSES) "DICTIONARY CACHE GET MISSES" 
FROM V$ROWCACHE 

--非系统用户建在SYSTEM表空间中的表
SELECT owner,table_name 
FROM DBA_TABLES
WHERE tablespace_name in('SYSTEM','USER_DATA') AND 
      owner NOT IN('SYSTEM','SYS','OUTLN', 'ORDSYS','MDSYS','SCOTT', 'HOSTEAC')

--性能最差的SQL
SELECT * FROM ( SELECT PARSING_USER_ID EXECUTIONS,SORTS,COMMAND_TYPE,DISK_READS,sql_text 
                FROM v$sqlarea 
                ORDER BY disk_reads DESC) 
WHERE ROWNUM<100
                             
--读磁盘数超100次的sql
select * from sys.v_$sqlarea where disk_reads>100

--最频繁执行的sql
select * from sys.v_$sqlarea where executions>100

--查询使用CPU多的用户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

--当前每个会话使用的对象数
SELECT a.sid,s.terminal,s.program,count(a.sid) 
FROM V$ACCESS a,V$SESSION s
WHERE a.owner <> 'SYS'AND s.sid = a.sid 
GROUP BY a.sid,s.terminal,s.program
ORDER BY count(a.sid)


--表占用的空间
select   a.segment_name,sum(bytes)/1024/1024   from   user_segments   a 
　　where   segment_type= 'TABLE'   
group   by   a.segment_name

 

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