db_cache_size、shared_pool_size一些初始化参数为什么是0？

http://blog.csdn.net/wh62592855/article/details/4873859

先来看一个“看起来”比较奇怪的现象

SQL> col name for a40

SQL> col value for a30

SQL> select name,value

2 from v$parameter

3 where name in

4 ('large_pool_size','java_pool_size','shared_pool_size','streams_pool_size',

'db_cache_size');

NAME VALUE

---------------------------------------- ------------------------------

shared_pool_size 0

large_pool_size 0

java_pool_size 0

streams_pool_size 0

db_cache_size 0

怎么回事，怎么会都是0呢？上REFERENCES查一下db_cache_size这个参数，其中有一句话如下：

If

SGA_TARGET

is set: If the parameter is not specified, then the default is

0

(internally determined by the Oracle Database). If the parameter is specified, then the user-specified value indicates a minimum value for the memory pool.

这下就很清楚了吧，因为使用了10G ASSM自动共享内存管理。

那么如何查看系统在某个时刻这些参数到底被自动的调整到了什么值呢？

SQL> select x.ksppinm name,y.ksppstvl value,x.ksppdesc describ

2 from sys.x$ksppi x,sys.x$ksppcv y

3 where x.inst_id=userenv('Instance')

4 and y.inst_id=userenv('Instance')

5 and x.indx=y.indx

6 and x.ksppinm like '%pool_size%'

7 /

NAME VALUE DESCRIB

-------------------- ---------- ----------------------------------------

_NUMA_pool_size Not specif aggregate size in bytes of NUMA pool

ied

__shared_pool_size 79691776 Actual size in bytes of shared pool

shared_pool_size 0 size in bytes of shared pool

__large_pool_size 4194304 Actual size in bytes of large pool

large_pool_size 0 size in bytes of large pool

__java_pool_size 4194304 Actual size in bytes of java pool

java_pool_size 0 size in bytes of java pool

__streams_pool_size 0 Actual size in bytes of streams pool

streams_pool_size 0 size in bytes of the streams pool

NAME VALUE DESCRIB

-------------------- ---------- ----------------------------------------

_io_shared_pool_size 4194304 Size of I/O buffer pool from SGA

_backup_io_pool_size 1048576 memory to reserve from the large pool

global_context_pool_ Global Application Context Pool Size in

size Bytes

olap_page_pool_size 0 size of the olap page pool in bytes

13 rows selected.

SQL> edit

Wrote file afiedt.buf

1 select x.ksppinm name,y.ksppstvl value,x.ksppdesc describ

2 from sys.x$ksppi x,sys.x$ksppcv y

3 where x.inst_id=userenv('Instance')

4 and y.inst_id=userenv('Instance')

5 and x.indx=y.indx

6* and x.ksppinm like '%db_cache_size%'

SQL> /

NAME VALUE DESCRIB

-------------------- ---------- ----------------------------------------

__db_cache_size 83886080 Actual size of DEFAULT buffer pool for s

tandard block size buffers

db_cache_size 0 Size of DEFAULT buffer pool for standard

block size buffers

从上面结果中黑体部分可以看到，这些由两个下划线开头的参数决定了当前SGA的分配，也是动态内存管理调整的参数。这些参数的更改会被记录到SPFILE文件中，在下一次数据库启动时仍然有效。

通过ORACLE 10G新增加的动态视图v$sga_dynamic_components，可以看各个动态组件调整的时间和调整类型等信息。

SQL> select component,current_size,min_size,last_oper_type,

2 last_oper_mode,to_char(last_oper_time,'yyyy-mm-dd hh24:mi:ss') LOT

3 from v$sga_dynamic_components

4 /

COMPONENT CURRENT_SIZE MIN_SIZE LAST_OPER_TYP LAST_OPER LOT

-------------------- ------------ ---------- ------------- --------- -----------

--------

shared pool 79691776 75497472 GROW IMMEDIATE 2009-11-25

20:11:08

large pool 4194304 4194304 STATIC

java pool 4194304 4194304 STATIC

streams pool 0 0 STATIC

DEFAULT buffer cache 83886080 83886080 SHRINK IMMEDIATE 2009-11-25

20:11:08

KEEP buffer cache 0 0 STATIC

RECYCLE buffer cache 0 0 STATIC

DEFAULT 2K buffer ca 0 0 STATIC

che

DEFAULT 4K buffer ca 0 0 STATIC

COMPONENT CURRENT_SIZE MIN_SIZE LAST_OPER_TYP LAST_OPER LOT

-------------------- ------------ ---------- ------------- --------- -----------

--------

che

DEFAULT 8K buffer ca 0 0 STATIC

che

DEFAULT 16K buffer c 0 0 STATIC

ache

DEFAULT 32K buffer c 0 0 STATIC

ache

COMPONENT CURRENT_SIZE MIN_SIZE LAST_OPER_TYP LAST_OPER LOT

-------------------- ------------ ---------- ------------- --------- -----------

--------

ASM Buffer Cache 0 0 STATIC

13 rows selected.