PGA中存储了用户会话数据，PGA大小由参数PGA_AGGREGATE_TARGET决定，

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show parameter pga_aggregate_target

NAME TYPE
------------------------------------ ----------------------
VALUE
------------------------------
pga_aggregate_target big integer
190M

可以通过查询V$PGA_TARGET_ADVICE，来判断PGA_AGGREGATE_TARGET设置得是否合理。Oracle会根据过去的负载来判断。

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select pga_target_for_estimate/1024/1024 "MB"
,estd_pga_cache_hit_percentage
from v$pga_target_advice
where estd_pga_cache_hit_percentage > 95;

MB ESTD_PGA_CACHE_HIT_PERCENTAGE
---------- -----------------------------
23.75 100
47.5 100
95 100
142.5 100
190 100
228 100
266 100
304 100
342 100
380 100
570 100

MB ESTD_PGA_CACHE_HIT_PERCENTAGE
---------- -----------------------------
760 100
1140 100
1520 100

如上例，最小可将PGA_AGGREGATE_TARGET设置为23.75MB。

SGA相关参数，

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show parameter sga_%

NAME TYPE
------------------------------------ ----------------------
VALUE
------------------------------
sga_max_size big integer
572M
sga_target big integer
572M

默认情况下，SGA各组件的初始参数为0，要查看实际使用状况，

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select component
,current_size/1024/1024 "Current MB"
,min_size/1024/1024 "Min MB"
from v$sga_dynamic_components

COMPONENT Current MB Min MB
------------------------------ ---------- ----------
shared pool 176 172
large pool 4 4
java pool 4 4
streams pool 0 0
DEFAULT buffer cache 380 380
KEEP buffer cache 0 0
RECYCLE buffer cache 0 0
DEFAULT 2K buffer cache 0 0
DEFAULT 4K buffer cache 0 0
DEFAULT 8K buffer cache 0 0
DEFAULT 16K buffer cache 0 0

COMPONENT Current MB Min MB
------------------------------ ---------- ----------
DEFAULT 32K buffer cache 0 0
ASM Buffer Cache 0 0

各组件总和大约等于SGA_TARGET。

观察PGA和SGA的使用状况