select size_for_estimate, buffers_for_estimate ,ESTD_PHYSICAL_READ_factor,ESTD_PHYSICAL_READS from v$db_cache_advice
2 where block_size='8192' and advice_status='ON';
中，size_for_estimate表示預計的數據庫高速緩衝區的大小（即：db_cache_size的值）。ESTD_PHYSICAL_READS表示預計的物理讀。
當增加數據庫高速緩衝區的的時候，物理讀（ESTD_PHYSICAL_READS）越少，說明命中率越高。
1.優化緩衝區大小、提高服務器的命中率
db_cache_size big integer 838860800
2.查看緩衝區命中率是否需要調優.
select 1 - ((physical.value - direct.value - lobs.value) / logical.value)
"Buffer Cache Hit Ratio"
from v$sysstat physical,v$sysstat direct,v$sysstat lobs,v$sysstat logical
where physical.name = 'physical reads'
and direct.name='physical reads direct'
and lobs.name='physical reads direct (lob)'
and logical.name='session logical reads';
當命中率>90%說明命中率很高了
3。獲取推薦的值
select name,size_for_estimate,v$db_cache_advice.ESTD_PHYSICAL_READS from v$db_cache_advice
where block_size='8192' and advice_status='ON';
set linesize 1000
---20100619Oracle9i數據 Solaris 9i操作系統
SQL> set linesize 1000
SQL> select size_for_estimate, buffers_for_estimate ,ESTD_PHYSICAL_READ_factor,ESTD_PHYSICAL_READS from v$db_cache_advice
where block_size='8192' and advice_status='ON';
SIZE_FOR_ESTIMATE BUFFERS_FOR_ESTIMATE ESTD_PHYSICAL_READ_FACTOR ESTD_PHYSICAL_READS
----------------- -------------------- ------------------------- -------------------
80 9925 28.9757 1436311200
160 19850 2.1053 104360120
240 29775 1.5819 78413087
320 39700 1.4262 70693980
400 49625 1.3543 67131735
480 59550 1.278 63349434
560 69475 1.1893 58954568
640 79400 1.1325 56135206
720 89325 1.0762 53347837
800 99250 1 49569438
880 109175 .7067 35030953
SIZE_FOR_ESTIMATE BUFFERS_FOR_ESTIMATE ESTD_PHYSICAL_READ_FACTOR ESTD_PHYSICAL_READS
----------------- -------------------- ------------------------- -------------------
960 119100 .3991 19784701
1040 129025 .2305 11423374
1120 138950 .1927 9552903
1200 148875 .1506 7466278
1280 158800 .1501 7438186
1360 168725 .1501 7438186
1440 178650 .1501 7438186
1520 188575 .1501 7438186
1600 198500 .1501 7438186
SIZE_FOR_ESTIMATE M 爲單位：
當SIZE_FOR_ESTIMATE=80M 的時候 ESTD_PHYSICAL_READS=1436311200
當SIZE_FOR_ESTIMATE=1120M 的時候 ESTD_PHYSICAL_READS=9552903
當SIZE_FOR_ESTIMATE=1280M 的時候 ESTD_PHYSICAL_READS=7438186
之後ESTD_PHYSICAL_READS固定了
所以應該過大db_cache_size=1120M的值使得
4.修改發現DB_cache_size太大了。過大SGA區域解決
alter system set db_cache_size=1120M
--sga設置太小了導致
SQL> alter system set db_cache_size=1120M;
alter system set db_cache_size=1120M
*
ERROR 位於第 1 行:
ORA-02097: 無法修改參數，因爲指定的值無效
ORA-00384: 沒有足夠的內存來增加高速緩存的大小
之前的值
sga_max_size big integer 1494715120
SQL>alter system set SGA_MAX_SIZE=3500M scope=spfile;
系統已更改。
重新啓動與關閉解決
SQL> shutdown immediate
數據庫已經關閉。
已經卸載數據庫。
ORACLE 例程已經關閉。
SQL> startup
ORACLE 例程已經啓動。
Total System Global Area 3675756336 bytes
Fixed Size 735024 bytes
Variable Size 2835349504 bytes
Database Buffers 838860800 bytes
Redo Buffers 811008 bytes
數據庫裝載完畢。
數據庫已經打開。
查看命中率\當前只有80的滿足要求
SQL> select size_for_estimate, buffers_for_estimate ,ESTD_PHYSICAL_READ_factor,ESTD_PHYSICAL_READS from v$db_cache_advice
2 where block_size='8192' and advice_status='ON';
SIZE_FOR_ESTIMATE BUFFERS_FOR_ESTIMATE ESTD_PHYSICAL_READ_FACTOR ESTD_PHYSICAL_READS
----------------- -------------------- ------------------------- -------------------
80 9925 1 1528
160 19850 1 1528
240 29775 1 1528
320 39700 1 1528
400 49625 1 1528
480 59550 1 1528
560 69475 1 1528
640 79400 1 1528
720 89325 1 1528
800 99250 1 1528
880 109175 1 1528
SIZE_FOR_ESTIMATE BUFFERS_FOR_ESTIMATE ESTD_PHYSICAL_READ_FACTOR ESTD_PHYSICAL_READS
----------------- -------------------- ------------------------- -------------------
960 119100 1 1528
1040 129025 1 1528
1120 138950 1 1528
1200 148875 1 1528
1280 158800 1 1528
1360 168725 1 1528
1440 178650 1 1528
1520 188575 1 1528
1600 198500 1 1528
命中率降低了？
SQL> select 1 - ((physical.value - direct.value - lobs.value) / logical.value)
2 "Buffer Cache Hit Ratio"
3 from v$sysstat physical,v$sysstat direct,v$sysstat lobs,v$sysstat logical
4 where physical.name = 'physical reads'
5 and direct.name='physical reads direct'
6 and lobs.name='physical reads direct (lob)'
7 and logical.name='session logical reads';
Buffer Cache Hit Ratio
----------------------
.906673167
繼續縮小SGA大小
SQL>alter system set SGA_MAX_SIZE=3000M scope=spfile;
SQL> shutdown immediate
數據庫已經關閉。
已經卸載數據庫。
ORACLE 例程已經關閉。
SQL> startup
ORACLE 例程已經啓動。
Total System Global Area 3155661888 bytes
Fixed Size 734272 bytes
Variable Size 2315255808 bytes
Database Buffers 838860800 bytes
Redo Buffers 811008 bytes
數據庫裝載完畢。
數據庫已經打開。
select size_for_estimate, buffers_for_estimate ,ESTD_PHYSICAL_READ_factor,ESTD_PHYSICAL_READS from v$db_cache_advice
where block_size='8192' and advice_status='ON';
繼續測試：等待30分鐘之後測試
SQL> alter system set db_cache_size=1120M;
select 1 - ((physical.value - direct.value - lobs.value) / logical.value)
"Buffer Cache Hit Ratio"
from v$sysstat physical,v$sysstat direct,v$sysstat lobs,v$sysstat logical
where physical.name = 'physical reads'
and direct.name='physical reads direct'
and lobs.name='physical reads direct (lob)'
and logical.name='session logical reads';
---命中率逐漸的提高了
---半個小時之後查詢命中率是98%
SQL> select 1 - ((physical.value - direct.value - lobs.value) / logical.value)
2 "Buffer Cache Hit Ratio"
3 from v$sysstat physical,v$sysstat direct,v$sysstat lobs,v$sysstat logical
4 where physical.name = 'physical reads'
5 and direct.name='physical reads direct'
6 and lobs.name='physical reads direct (lob)'
7 and logical.name='session logical reads';
Buffer Cache Hit Ratio
----------------------
.980309028
-----查詢推薦的值
show parameter db_block_size
8192
select name,size_for_estimate,v$db_cache_advice.ESTD_PHYSICAL_READS from
v$db_cache_advice where block_size='8192' and advice_status='ON';
NAME SIZE_FOR_ESTIMATE ESTD_PHYSICAL_READS
-------------------- ----------------- -------------------
DEFAULT 112 9581
DEFAULT 224 9514
DEFAULT 336 9514
DEFAULT 448 9514
DEFAULT 560 9514
DEFAULT 672 9514
DEFAULT 784 9514
DEFAULT 896 9514
DEFAULT 1008 9514
DEFAULT 1120 9514
DEFAULT 1232 9514
NAME SIZE_FOR_ESTIMATE ESTD_PHYSICAL_READS
-------------------- ----------------- -------------------
DEFAULT 1344 9514
DEFAULT 1456 9514
DEFAULT 1568 9514
DEFAULT 1680 9514
DEFAULT 1792 9514
DEFAULT 1904 9514
DEFAULT 2016 9514
DEFAULT 2128 9514
DEFAULT 2240 9514
顯示只要112M大小的空間就可以穩定降低ESTD_PHYSICAL_READS
alter system set db_cache_size=112M
NAME SIZE_FOR_ESTIMATE ESTD_PHYSICAL_READS
-------------------- ----------------- -------------------
DEFAULT 16 0
DEFAULT 32 0
DEFAULT 48 0
DEFAULT 64 0
DEFAULT 80 0
DEFAULT 96 0
DEFAULT 112 0
DEFAULT 128 0
DEFAULT 144 0
DEFAULT 160 0
DEFAULT 176 0
NAME SIZE_FOR_ESTIMATE ESTD_PHYSICAL_READS
-------------------- ----------------- -------------------
DEFAULT 192 0
DEFAULT 208 0
DEFAULT 224 0
DEFAULT 240 0
DEFAULT 256 0
DEFAULT 272 0
DEFAULT 288 0
DEFAULT 304 0
DEFAULT 320 0
---查看命中率
select 1 - ((physical.value - direct.value - lobs.value) / logical.value)
"Buffer Cache Hit Ratio"
from v$sysstat physical,v$sysstat direct,v$sysstat lobs,v$sysstat logical
where physical.name = 'physical reads'
and direct.name='physical reads direct'
and lobs.name='physical reads direct (lob)'
and logical.name='session logical reads';
Buffer Cache Hit Ratio
----------------------
.982795739
說明Oracle更換峯值的情況決定db_cache_size的大小。
所以設置最大峯值滿足的情況。
alter system set db_cache_size=1120M;滿足峯值的時候最大值
select name,size_for_estimate,v$db_cache_advice.ESTD_PHYSICAL_READS from
v$db_cache_advice where block_size='8192' and advice_status='ON';
oracle10g Solaris 10 sparc系統調整
--查
select name,size_for_estimate,v$db_cache_advice.ESTD_PHYSICAL_READS from
v$db_cache_advice where block_size='8192' and advice_status='ON';
-------------------- ----------------- -------------------
DEFAULT 128 1206647
DEFAULT 256 1067789
DEFAULT 384 987752
DEFAULT 512 965164
DEFAULT 640 913815
DEFAULT 768 893485
DEFAULT 896 867321
DEFAULT 1024 808884
DEFAULT 1152 599909
DEFAULT 1280 344618
--此時開始保持在一個穩定的讀取值
alter system set db_cache_size=1196M
DEFAULT 1296 321763
NAME SIZE_FOR_ESTIMATE ESTD_PHYSICAL_READS
-------------------- ----------------- -------------------
DEFAULT 1408 285030
DEFAULT 1536 280506
DEFAULT 1664 280325
DEFAULT 1792 279816
DEFAULT 1920 266871
DEFAULT 2048 235838
DEFAULT 2176 231298
DEFAULT 2304 228483
DEFAULT 2432 224971
DEFAULT 2560 219467
--修改
alter system set db_cache_size=1196M
--查看命中率
select 1 - ((physical.value - direct.value - lobs.value) / logical.value)
"Buffer Cache Hit Ratio"
from v$sysstat physical,v$sysstat direct,v$sysstat lobs,v$sysstat logical
where physical.name = 'physical reads'
and direct.name='physical reads direct'
and lobs.name='physical reads direct (lob)'
and logical.name='session logical reads';