資料庫效能監控

1. 監控事例的等待

select event,sum(decode(wait_Time,0,0,1)) "rev",
sum(decode(wait_Time,0,1,0)) "Curr",count(*) "Tot"
from v$session_Wait
group by event order by 4;

2. 回滾段的爭用情況

select name, waits, gets, waits/gets "Ratio"
from v$rollstat a, v$rollname b
where a.usn = b.usn;

3. 監控表空間的 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;

4. 監控檔案系統的 I/O 比例

select substr(a.file#,1,2) "#", substr(a.name,1,30) "Name",
a.status, a.bytes, b.phyrds, b.phywrts
from v$datafile a, v$filestat b
where a.file# = b.file#;

5.在某個使用者下找所有的索引

select user_indexes.table_name, user_indexes.index_name,uniqueness, column_name
from user_ind_columns, user_indexes
where user_ind_columns.index_name = user_indexes.index_name
and user_ind_columns.table_name = user_indexes.table_name
order by user_indexes.table_type, user_indexes.table_name,
user_indexes.index_name, column_position;

6. 監控 SGA 的命中率

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;

7. 監控 SGA 中字典緩衝區的命中率

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;

8. 監控 SGA 中共享快取區的命中率，應該小於1%

select sum(pins) "Total Pins", sum(reloads) "Total Reloads",
sum(reloads)/sum(pins) *100 libcache
from v$librarycache;

select sum(pinhits-reloads)/sum(pins) "hit radio",sum(reloads)/sum(pins) "reload percent"
from v$librarycache;

9. 顯示所有物件的類別和大小

select count(name) num_instances ,type ,sum(source_size) source_size ,
sum(parsed_size) parsed_size ,sum(code_size) code_size ,sum(error_size) error_size,
sum(source_size) +sum(parsed_size) +sum(code_size) +sum(error_size) size_required
from dba_object_size
group by type order by 2;

10. 監控 SGA 中重做日誌快取區的命中率，應該小於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');

11.  監控記憶體和硬碟的排序比率，最好使它小於 .10，增加 sort_area_size

SELECT name, value FROM v$sysstat WHERE name IN ('sorts (memory)', 'sorts (disk)');

12. 監控當前資料庫誰在執行什麼語句

SELECT osuser, username, sql_text from v$session a, v$sqltext b
where a.sql_address =b.address order by address, piece;

13. 監控字典緩衝區

SELECT (SUM(PINS - RELOADS)) / SUM(PINS) "LIB CACHE" FROM V$LIBRARYCACHE;
SELECT (SUM(GETS - GETMISSES - USAGE - FIXED)) / SUM(GETS) "ROW CACHE" FROM V$ROWCACHE;
SELECT SUM(PINS) "EXECUTIONS", SUM(RELOADS) "CACHE MISSES WHILE EXECUTING" FROM V$LIBRARYCACHE;

後者除以前者,此比率小於1%,接近0%為好。

SELECT SUM(GETS) "DICTIONARY GETS",SUM(GETMISSES) "DICTIONARY CACHE GET MISSES"
FROM V$ROWCACHE

14. 找字符集

select * from sys.props$ where name='NLS_CHARACTERSET';

15. 監控 MTS

select busy/(busy+idle) "shared servers busy" from v$dispatcher;

此值大於0.5時，引數需加大

select sum(wait)/sum(totalq) "dispatcher waits" from v$queue where type='dispatcher';
select count(*) from v$dispatcher;
select servers_highwater from v$mts;

servers_highwater接近mts_max_servers時，引數需加大

16. 碎片程度

select tablespace_name,count(tablespace_name) from dba_free_space group by tablespace_name
having count(tablespace_name)>;10;

alter tablespace name coalesce;
alter table name deallocate unused;

create or replace view ts_blocks_v as
select tablespace_name,block_id,bytes,blocks,'free space' segment_name from dba_free_space
union all
select tablespace_name,block_id,bytes,blocks,segment_name from dba_extents;

select * from ts_blocks_v;

select tablespace_name,sum(bytes),max(bytes),count(block_id) from dba_free_space
group by tablespace_name;

檢視碎片程度高的表

SELECT segment_name table_name , COUNT(*) extents
FROM dba_segments WHERE owner NOT IN ('SYS', 'SYSTEM') GROUP BY segment_name
HAVING COUNT(*) = (SELECT MAX( COUNT(*) ) FROM dba_segments GROUP BY segment_name);

17. 表、索引的儲存情況檢查

select segment_name,sum(bytes),count(*) ext_quan from dba_extents where
tablespace_name='&tablespace_name' and segment_type='TABLE' group by tablespace_name,segment_name;

select segment_name,count(*) from dba_extents where segment_type='INDEX' and wner='&owner'
group by segment_name;

18、找使用CPU多的使用者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;

監 控資料庫狀態的目的就是找到相關的瓶頸點，但也許有時你的監控語句就會是你的瓶頸點，包括您後臺的一些自動的監控。Jason就遇到這樣的囧事，不是 dbconsole佔資源（響應時間>2s）就是監控lock語句佔資源,包括oracle的某些maintain功能，需要很好的時間 schedual。

插播就到這裡，下篇會繼續負載均衡，我們的重點是比較流行的lvs heartbeat。