第八讲--buffer cache大小的设置及依据
查看oracle相关进程：
[oracle@redhat4 ~]$ ps -ef|grep ora root 8450 7935 0 10:40 pts/1 00:00:00 su - oracle oracle 8451 8450 0 10:40 pts/1 00:00:00 -bash oracle 8480 1 0 10:41 ? 00:00:00 ora_pmon_jiagulun oracle 8482 1 0 10:41 ? 00:00:00 ora_psp0_jiagulun oracle 8484 1 0 10:41 ? 00:00:00 ora_mman_jiagulun oracle 8486 1 0 10:41 ? 00:00:00 ora_dbw0_jiagulun oracle 8488 1 0 10:41 ? 00:00:00 ora_lgwr_jiagulun oracle 8490 1 0 10:41 ? 00:00:00 ora_ckpt_jiagulun oracle 8492 1 0 10:41 ? 00:00:00 ora_smon_jiagulun oracle 8494 1 0 10:41 ? 00:00:00 ora_reco_jiagulun oracle 8496 1 0 10:41 ? 00:00:00 ora_cjq0_jiagulun oracle 8498 1 0 10:41 ? 00:00:00 ora_mmon_jiagulun oracle 8500 1 0 10:41 ? 00:00:00 ora_mmnl_jiagulun oracle 8502 1 0 10:41 ? 00:00:00 ora_d000_jiagulun oracle 8504 1 0 10:41 ? 00:00:00 ora_s000_jiagulun oracle 8540 1 0 10:41 ? 00:00:00 ora_qmnc_jiagulun oracle 8542 1 0 10:41 ? 00:00:00 ora_j000_jiagulun oracle 8560 1 0 10:41 ? 00:00:00 ora_q000_jiagulun oracle 8562 1 0 10:41 ? 00:00:00 ora_q001_jiagulun oracle 8681 8451 0 10:42 pts/1 00:00:00 ps -ef oracle 8682 8451 0 10:42 pts/1 00:00:00 grep ora SQL> show parameter writer
发现有一个进程叫做dbw0，有0就有1，在oracle中DBWR进程不止一个，一般是CPU数量除以8。
查看SGA各个组件大小：
SQL>select component,current_size,min_size from v$sga_dynamic_components; COMPONENT CURRENT_SIZE<pre name="code" class="plain">MIN_SIZE---------------------------------------------------sharedpool 150994944 146800640 largepool 4194304 4194304 javapool 4194304 4194304 COMPONENT CURRENT_SIZE---------------------------------------------------------------------------- MIN_SIZE----------streamspool 0 0 DEFAULTbuffer cache 117440512 117440512 KEEPbuffer cache 0 0 COMPONENT CURRENT_SIZE---------------------------------------------------------------------------- MIN_SIZE----------RECYCLEbuffer cache 0 0 DEFAULT2K buffer cache 0 0 DEFAULT4K buffer cache 0 0 COMPONENT CURRENT_SIZE---------------------------------------------------------------------------- MIN_SIZE----------DEFAULT8K buffer cache 0 0 DEFAULT16K buffer cache 0 0 DEFAULT32K buffer cache 0 0 COMPONENT CURRENT_SIZE---------------------------------------------------------------------------- MIN_SIZE----------ASMBuffer Cache 0 0 13 rowsselected.
SQL>select component,current_size,min_size from v$sga_dynamic_components;
COMPONENT CURRENT_SIZE
----------------------------------------------------------------------------
MIN_SIZE
----------
sharedpool 150994944
146800640
largepool 4194304
4194304
javapool 4194304
4194304
COMPONENT CURRENT_SIZE
----------------------------------------------------------------------------
MIN_SIZE
----------
streamspool 0
0
DEFAULTbuffer cache 117440512
117440512
KEEPbuffer cache 0
0
COMPONENT CURRENT_SIZE
----------------------------------------------------------------------------
MIN_SIZE
----------
RECYCLEbuffer cache 0
0
DEFAULT2K buffer cache 0
0
DEFAULT4K buffer cache 0
0
COMPONENT CURRENT_SIZE
----------------------------------------------------------------------------
MIN_SIZE
----------
DEFAULT8K buffer cache 0
0
DEFAULT16K buffer cache 0
0
DEFAULT32K buffer cache 0
0
COMPONENT CURRENT_SIZE
----------------------------------------------------------------------------
MIN_SIZE
----------
ASMBuffer Cache 0
0
13 rowsselected.
设置buffer cache大小：
Buffer cache的大小在SQL语句里叫做db_cache_size，推荐的配置是：db_cache_size=sga_max_size/2~sga_max_size*(2/3)。
先增加sga_max_size的大小（需要重启数据库）；再增加sga_target的大小；最后增加db_cache_size的大小；
1. Altersystem set sga_max_size scope=both;
2. Altersystem set sga_target=200m scope=both;
3. Shutdownimmediate;
4. Startup;
5. Altersystem set db_cache_size=100m scope=both;