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oraclePGA管理(算法)

來源：懂視網(wǎng) 責(zé)編：小采時間：2020-11-09 07:22:20

oraclePGA管理(算法)

oraclePGA管理(算法):主要總結(jié)下pga分配算法,詳細(xì)概念單總結(jié) 簡單理解pga,pga就是一個操作系統(tǒng)進(jìn)程,或線程(WIN上)的專用內(nèi)存 pmon,smon這些后臺進(jìn)程都有自己的pga pga早期手動管理組成由sort_area_size,hash_area_size,bitmap_merge_size,create

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導(dǎo)讀oraclePGA管理(算法):主要總結(jié)下pga分配算法,詳細(xì)概念單總結(jié) 簡單理解pga,pga就是一個操作系統(tǒng)進(jìn)程,或線程(WIN上)的專用內(nèi)存 pmon,smon這些后臺進(jìn)程都有自己的pga pga早期手動管理組成由sort_area_size,hash_area_size,bitmap_merge_size,create

主要總結(jié)下pga分配算法,詳細(xì)概念單總結(jié) 簡單理解pga,pga就是一個操作系統(tǒng)進(jìn)程,或線程(WIN上)的專用內(nèi)存 pmon,smon這些后臺進(jìn)程都有自己的pga pga早期手動管理組成由sort_area_size,hash_area_size,bitmap_merge_size,create_bitmap_area_size(這些都叫工作

主要總結(jié)下pga分配算法,詳細(xì)概念單總結(jié)

簡單理解pga,pga就是一個操作系統(tǒng)進(jìn)程,或線程(WIN上)的專用內(nèi)存
pmon,smon這些后臺進(jìn)程都有自己的pga

pga早期手動管理組成由sort_area_size,hash_area_size,bitmap_merge_size,create_bitmap_area_size(這些都叫工作區(qū))
手動缺點，不好回收和共享，會造成PGA內(nèi)存過度消耗

PAG自動（9i開始支持）
1.pga_aggregate_target來指定所有session總計可以使用的最大pga內(nèi)存（10M-4096G）
2.workarea_size_policy控制pag自動管理功能開啟或關(guān)閉，auto表示開啟（default）， manual表示關(guān)閉，9i auto只支持專用連接，共享連接不支持
10g都支持

_pga_max_size:控制pga最大大小
9i-10r1中,單個sql操作內(nèi)存使用現(xiàn)在
1.對于串行操作,單sql操作pga分配原則,min(5%*pga_aggregate_target,100mb)
########5%*pga_aggregate_targe實際由_smm_max_size控制]
2.并行操作使用pga按 30%*pga_aggregate_target/dop(dop=并行度)

9I _pga_max_size與_smm_max_size
_pga_max_size>5%*pga_aggregate_target,_smm_max_size=5%*pga_aggregate_target'
_pga_max_size<5%*pga_aggregate_target,_smm_max_size=50*_pga_max_size

used_pga_mb=min(5%*pga_aggregate_target,50*_pga_max_size,_smm_max_size)

10r2,11g原則
1.串行操作
pga_aggregate_target<=500MB,_smm_max_size=20%*pga_aggregate_target
pga_aggregate_target between 500m and 1000M ,_smm_max_size=100M
pga_aggregate_target between 1001m and 2.5g,_smm_max_size=10%*pga_aggregate_target
pga_aggregate_target >2.5g,_smm_max_size=0.25GB
2.并行操作
50*pag_aggregate_target/dop
dop<=5時,_smm_max_size生效
dop>5時,_smm_px_max_size生效

_newsort_enabled 控制算法規(guī)則,true用10g新算法,false用9i算法
SQL> set linesize 132
SQL> column name format a30
SQL> column value format a25
SQL> SELECT x.ksppinm NAME, y.ksppstvl VALUE, x.ksppdesc describ
2 FROM SYS.x$ksppi x, SYS.x$ksppcv y
3 WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
4
SQL> /
Enter value for par: newsort
old 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
new 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%newsort%'

NAME VALUE
------------------------------ -------------------------
DESCRIB
------------------------------------------------------------------------------------------------------------------------------------
_newsort_enabled TRUE
controls whether new sorts can be used as system sort

設(shè)置建議
1.oltp系統(tǒng) pag_aggregate_target=*80%*20%
2.dss系統(tǒng) pag_aggregate_target=*80%*50%
分析:留20%給os,其他80%給pga+sga,oltp ,pga占 80%中20%,dss占80%中50%

#查看某個process使用情況
select pid,spid,username ,pga_used_mem,pga_alloc_mem,pga_freeable_mem,pga_max_mem,program from v$process where spid=&spid

SQL> select pid,spid,username ,pga_used_mem,pga_alloc_mem,pga_freeable_mem,pga_max_mem,program from v$process where spid=&spid;
Enter value for spid: 25510
old 1: select pid,spid,username ,pga_used_mem,pga_alloc_mem,pga_freeable_mem,pga_max_mem,program from v$process where spid=&spid
new 1: select pid,spid,username ,pga_used_mem,pga_alloc_mem,pga_freeable_mem,pga_max_mem,program from v$process where spid=25510

PID SPID USERNAME PGA_USED_MEM PGA_ALLOC_MEM
---------- ------------------------ --------------- ------------ -------------
PGA_FREEABLE_MEM PGA_MAX_MEM PROGRAM
---------------- ----------- ------------------------------------------------
33 25510 oracle 0 2664666
983040 8431834oracle@dmk01(PZ98)

pga_used_mem:進(jìn)程使用的pga
pga_alloc_mem:分配給進(jìn)程的pga
pga_freeable_mem:空閑
pga_max_mem:進(jìn)程使用pga內(nèi)存的最大

#查看pga消耗到哪些項目上了
col program for a20
set linesize 1000
select p.program,p.pid,pm.category,pm.allocated,pm.used,pm.max_allocated from v$process p,v$process_memory pm where p.pid=pm.pid and p.spid=&spid;

SQL> col program for a20
SQL> set linesize 1000
SQL> select p.program,p.pid,pm.category,pm.allocated,pm.used,pm.max_allocated from v$process p,v$process_memory pm where p.pid=pm.pid and p.spid=&spid;
Enter value for spid: 25510
old 1: select p.program,p.pid,pm.category,pm.allocated,pm.used,pm.max_allocated from v$process p,v$process_memory pm where p.pid=pm.pid and p.spid=&spid
new 1: select p.program,p.pid,pm.category,pm.allocated,pm.used,pm.max_allocated from v$process p,v$process_memory pm where p.pid=pm.pid and p.spid=25510

PROGRAM PID CATEGORY ALLOCATED USED MAX_ALLOCATED
-------------------- ---------- --------------- ---------- ---------- -------------
oracle@dmk01(PZ98) 33 SQL 0 0 2424808
oracle@dmk01(PZ98) 33 PL/SQL 24840 17104 26928
oracle@dmk01(PZ98) 33 Freeable 983040 0
oracle@dmk01(PZ98) 33 Other 1656786 4997058

sql在workare中有3種方式
1.optimal:最優(yōu)方式,所有處理可以在內(nèi)存中完成
2.onepass:大部分操作可以在內(nèi)存中完成,但交換到臨時表一次
3.multipass:多變交互臨時表,產(chǎn)生大量disk sort之類,性能最差

oracle建議
workarea execution_optimal>=90%
workarea execution_multipass=0%
#查看系統(tǒng)中性能指標(biāo)
select name,value,100*(value/decode((select sum(value) from v$sysstat where name like 'workarea execution%'),0,null,(select sum(value) from v$sysstat where name like 'workarea execution%')))pct from v$sysstat where name like 'workarea executions%';

SQL> select name,value,100*(value/decode((select sum(value) from v$sysstat where name like 'workarea execution%'),0,null,(select sum(value) from v$sysstat where name like 'workarea execution%')))pct from v$sysstat where name like 'workarea executions%';

NAME VALUE PCT
---------------------------------------------------------------- ---------- ----------
workarea executions - optimal 567832 99.9954214
workarea executions - onepass 24 .004226409
workarea executions - multipass 0 0

#查單個sql語句workarea使用情況
SELECT
b.sql_text,
a.operation_type,
a.policy,
a.last_memory_used/(1024*1024) as "Used MB" ,
a.estimated_optimal_size/(1024*1024) as "Est Opt MB",
a.estimated_onepass_size/(1024*1024) as "Est OnePass MB",
a.last_execution,
a.last_tempseg_size
FROM v$sql_workarea a,v$sql b
WHERE a.hash_value = b.hash_value
and a.hash_value = &hashvalue
/

#查session 使用pga
select a.name, b.value
from v$statname a, v$sesstat b
where a.statistic# = b.statistic#
and b.sid = &sid
and a.name like '%ga %'
order by a.name
/

#program 使用pga情況
SELECT
a.pga_used_mem "PGA Used",
a.pga_alloc_mem "PGA Alloc",
a.pga_max_mem "PGA Max"
FROM v$process a,v$session b
where a.addr = b.paddr
and b.sid= &sid
/

關(guān)于pga自動管理算法：
oracle 采用的feedback loop實現(xiàn)的，當(dāng)一個process執(zhí)行sql語句時,先用local memory manager注冊一個active workarea profile,workarea profile是與內(nèi)存管理器之間唯一的通信接口
(既sql語句和內(nèi)存管理器之間唯一接口),當(dāng)sql語句執(zhí)行完成對應(yīng)的workarea profile刪除
,profile含這個workarea很多屬性（例如sql類型是hash join還是什么之類，執(zhí)行one pass,optimal操作內(nèi)存大小等的元數(shù)據(jù)）
workarea active profile集，通過local memory manager維護(hù)，存sga中,profile常常被更新(要求及時反映sql語句當(dāng)前已消耗內(nèi)存，及是否被交換到temp tablespace等信息)，
所以active profile基本上就是pga內(nèi)存需要和當(dāng)前正在使用的pga內(nèi)存,通過這些profile信息
,global memory manager會計算出一個既可以限制內(nèi)存使用又可以提高較好性能的global memory bound,這個值用于限制單個進(jìn)程pga的上限，global memory manager每3S更新一次memory
bound,local memory manager得到memory bound后會計算每個active statement所需要分配的pga內(nèi)存大小（execute size），然后每個active statement將會在自己所分配到的execute size
中計算

路線(一個環(huán)路)
active statement--->注冊workarea profile-->local memory manager(存sga中)-->set of active workarea profiles-->global memory manager--->計算出memory bound--->local memory manager
--->獲取workarea size--->active statement

其實原理很簡單，就是每個sql語句拿出信息做成profile，然后交給local memory manager 然后做成profile集（大量profile），然后global memory manager通過profile集計算出memory bound
，把這個memory bound給 local memory manager，local memory manager 用memory bound計算出每個active statement的 execute size，然后每個active statement在自己分到的execute
size中計算

global memeory bound將影響所有進(jìn)程pga分配（限制單個進(jìn)程pga的上限）

由ckpt實現(xiàn),global memory manager 3s更新一次memory bound

SQL> select description ,dest from x$messages where lower(description) like 'sql memory%';

DESCRIPTION
----------------------------------------------------------------
DEST
----------------------------------------------------------------
SQL Memory Management Calculation
CKPT

SQL> select time,data from x$trace where lower(data) like '%sql memory%' order by seq#;

TIME
----------
DATA
--------------------------------------------------------------------------------
1.2688E+15
KSBCTI: (CKPT) : (timeout action) : acnum=[178] comment=[SQL Memory Management
Calculation]

1.2688E+15
KSBCTI: (CKPT) : (timeout action) : acnum=[178] comment=[SQL Memory Management
Calculation]

1.2688E+15

TIME
----------
DATA
--------------------------------------------------------------------------------
KSBCTI: (CKPT) : (timeout action) : acnum=[178] comment=[SQL Memory Management
Calculation]

10g r2,11g中，workarea管理內(nèi)存分配，存在shared pool中（local memory manager）
SQL> select * from v$sgastat where name like 'work area%';

POOL NAME BYTES
------------ -------------------------- ----------
shared pool work area tab 265320

10g 測試

SQL> select * from v$version;

BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - Prod
PL/SQL Release 10.2.0.4.0 - Production
CORE 10.2.0.4.0 Production
TNS for Linux: Version 10.2.0.4.0 - Production
NLSRTL Version 10.2.0.4.0 - Production

SQL> set linesize 132
SQL> column name format a30
SQL> column value format a25
SQL> SELECT x.ksppinm NAME, y.ksppstvl VALUE, x.ksppdesc describ
2 FROM SYS.x$ksppi x, SYS.x$ksppcv y
3 WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
4
SQL> /
Enter value for par: pga_max
old 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
new 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%pga_max%'

NAME VALUE
------------------------------ -------------------------
DESCRIB
------------------------------------------------------------------------------------------------------------------------------------
_pga_max_size 209715200
Maximum size of the PGA memory for one process

可以看到當(dāng)pga_aggreate_target小于1g,_pga_max_size 默認(rèn)為200MB

SQL> /
Enter value for par: smm_max
old 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
new 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%smm_max%'

NAME VALUE
------------------------------ -------------------------
DESCRIB
------------------------------------------------------------------------------------------------------------------------------------
_smm_max_size 26214
maximum work area size in auto mode (serial)

pga_aggregate_target <500M,_smm_max_size 默認(rèn)為20%pga_aggregate_target=25.6M(其實_smm_max_size實際與_pga_max_size還有關(guān)系,單相關(guān)算發(fā)已經(jīng)不是9i的了,下面會證實)

SQL> show parameter pga

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
pga_aggregate_target big integer 128M
SQL>

SQL> select 26214/1024 from dual;

26214/1024
----------
25.5996094

SQL> select 0.2*128 from dual;

0.2*128
----------
25.6

_smm_max_size = 20%*pga_aggregate_target

修改_pga_max_size=10MB pga_aggregate_target =128M

SQL> alter system set "_pga_max_size"=10m;

System altered.

SQL> startup force 重起下庫,讓內(nèi)存重新計算
ORACLE instance started.

Table dropped.

SQL> create table t as select * from dba_objects;

Table created.

SQL> insert into t select * from dba_objects;

50067 rows created.

SQL> insert into t select * from dba_objects;

50067 rows created.

SQL> commit;

Commit complete.

SQL> select distinct sid from v$mystat;

SID
----------
159

SQL> show parameter pga

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
_pga_max_size big integer 10M
pga_aggregate_target big integer 128M
SQL> set linesize 132
column name format a30
SQL> SQL> column value format a25
SQL> SELECT x.ksppinm NAME, y.ksppstvl VALUE, x.ksppdesc describ
2 FROM SYS.x$ksppi x, SYS.x$ksppcv y
3 WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
4
SQL> /
Enter value for par: pga_max
old 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
new 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%pga_max%'

NAME VALUE
------------------------------ -------------------------
DESCRIB
------------------------------------------------------------------------------------------------------------------------------------
_pga_max_size 10485760
Maximum size of the PGA memory for one process
可以看到已經(jīng)生效,單位字節(jié)=10M

SQL> set linesize 132
SQL> column name format a30
SQL> column value format a25
SQL> SELECT x.ksppinm NAME, y.ksppstvl VALUE, x.ksppdesc describ
2 FROM SYS.x$ksppi x, SYS.x$ksppcv y
3 WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
4
SQL> /
Enter value for par: smm_max
old 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
new 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%smm_max%'

NAME VALUE
------------------------------ -------------------------
DESCRIB
------------------------------------------------------------------------------------------------------------------------------------
_smm_max_size 5120
maximum work area size in auto mode (serial)

可以看到 _smm_max_size 此時并不等于 20%*pga_aggregate_target而是 =5m 既50%_pga_max_size

SQL> select 10485760/1024/1024 from dual;

10485760/1024/1024
------------------
10

SQL> select 5120/1024 from dual;

5120/1024
----------
5

SQL> set autotrace traceonly stat
SQL> select * from t where rownum<50000 order by 1,2,3,4,5,6,7;

49999 rows selected.

Statistics
----------------------------------------------------------
37 recursive calls
8 db block gets
835 consistent gets
1382 physical reads
0 redo size
2837037 bytes sent via SQL*Net to client
37063 bytes received via SQL*Net from client
3335 SQL*Net roundtrips to/from client
0 sorts (memory)
1 sorts (disk)
49999 rows processed

SQL> select hash_value from v$sql where sql_text='select * from t where rownum<50000 order by 1,2,3,4,5,6,7'
2 ;

HASH_VALUE
----------
1281487883

SQL> SELECT
b.sql_text,
2 3 a.operation_type,
4 a.policy,
5 a.last_memory_used/(1024*1024) as "Used MB" ,
6 a.estimated_optimal_size/(1024*1024) as "Est Opt MB",
7 a.estimated_onepass_size/(1024*1024) as "Est OnePass MB",
8 a.last_execution,
9 a.last_tempseg_size
10 FROM v$sql_workarea a,v$sql b
11 WHERE a.hash_value = b.hash_value
12 and a.hash_value = &hashvalue
13 /
Enter value for hashvalue: 1281487883
old 12: and a.hash_value = &hashvalue
new 12: and a.hash_value = 1281487883

SQL_TEXT
--------------------------------------------------------------------------------
OPERATION_TYPE POLICY Used MB Est Opt MB Est OnePass MB LAST_EXECU
-------------------- ---------- ---------- ---------- -------------- ----------
LAST_TEMPSEG_SIZE
-----------------
select * from t where rownum<50000 order by 1,2,3,4,5,6,7
SORT (v2) AUTO 5.02832031 6.09960938 .98828125 1 PASS
6291456

可以看到內(nèi)存被限制在5M內(nèi),現(xiàn)在操作是1 pass,如果最優(yōu)操作(全在內(nèi)存里需要6M)
所以_smm_max_size就可以限制一個process pga內(nèi)存最大使用

此時_smm_max_size=5m是如下計算
1._pga_max_size<40%*pga_aggregate_size,此時_smm_max_size=50%_pga_max_size
2._pga_max_size>40%*pga_aggregate_siz,此時_smm_max_size按下面方式計算

pga_aggregate_target<=500MB,_smm_max_size=20%*pga_aggregate_target
pga_aggregate_target between 500m and 1000M ,_smm_max_size=100M
pga_aggregate_target between 1001m and 2.5g,_smm_max_size=10%*pga_aggregate_target
pga_aggregate_target >2.5g,_smm_max_size=0.25GB

修改pga_aggregate_target超過500m
SQL> alter system set pga_aggregate_target=501m;

System altered.

SQL> startup force
ORACLE instance started.

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
_pga_max_size big integer 10M ~~~~~~~~~還未10MB
pga_aggregate_target big integer 501M
SQL>

SQL> set linesize 132
SQL> column name format a30
SQL> column value format a25
SELECT x.ksppinm NAME, y.ksppstvl VALUE, x.ksppdesc describ
SQL> 2 FROM SYS.x$ksppi x, SYS.x$ksppcv y
3 WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
4
SQL> /
Enter value for par: pga_max
old 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
new 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%pga_max%'

NAME VALUE
------------------------------ -------------------------
DESCRIB
------------------------------------------------------------------------------------------------------------------------------------
_pga_max_size 10485760
Maximum size of the PGA memory for one process

SQL> /
Enter value for par: smm_max
old 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
new 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%smm_max%'

NAME VALUE
------------------------------ -------------------------
DESCRIB
------------------------------------------------------------------------------------------------------------------------------------
_smm_max_size 5120 ~~~~~~~~~~~~~~~還為5M 單位kb
maximum work area size in auto mode (serial)

通過這個可以發(fā)現(xiàn) 影響_smm_max_size調(diào)整最直接相關(guān)的參數(shù)為_pga_max_size,由于_pga_max_size未調(diào)整. _smm_max_size沒變
所以可以得出結(jié)論pga_aggreate_target影響_pga_max_size,_pga_max_size影響_smm_max_size

可以看到雖然pga_aggregate_target設(shè)置了501M,_PGA_MAX_SIZE應(yīng)該為200M 自動調(diào)整為，但由于_pga_max_size手動調(diào)整的，所以要手動reset下讓它自動默認(rèn)（這樣就自動計算了）
SQL> alter system reset "_pga_max_size" scope=spfile sid='*' ;

System altered.

SQL> startup force
ORACLE instance started

Total System Global Area 268435456 bytes
Fixed Size 1266944 bytes
Variable Size 100666112 bytes
Database Buffers 159383552 bytes
Redo Buffers 7118848 bytes
Database mounted.
Database opened.
SQL> set linesize 132
SQL> column name format a30
SQL> column value format a25
SQL> SELECT x.ksppinm NAME, y.ksppstvl VALUE, x.ksppdesc describ
2 FROM SYS.x$ksppi x, SYS.x$ksppcv y
3 WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
4
SQL> /
Enter value for par: pga_max
old 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
new 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%pga_max%'

NAME VALUE
------------------------------ -------------------------
DESCRIB
------------------------------------------------------------------------------------------------------------------------------------
_pga_max_size 209715200 ~~~~~~~~~
Maximum size of the PGA memory for one process

按算發(fā)pga_aggreate_target<1g,_pga_max_size =200m

SQL> /
Enter value for par: smm_max
old 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
new 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%smm_max%'

NAME VALUE
------------------------------ -------------------------
DESCRIB
------------------------------------------------------------------------------------------------------------------------------------
_smm_max_size 102400
maximum work area size in auto mode (serial)

SQL> show parameter pga

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
pga_aggregate_target big integer 501M
SQL>

102400/1024=100MB正好100MB
可以看到_pga_max_size=200M(pga_aggreate_target<1g,_pga_max_size default =200m)，按表面算法pga_aggreate_target>500M _smm_max_size 為100MB
而實際內(nèi)部因為
_pga_max_size=200M<40%*pga_aggregate_target,所以_smm_max_size =100M（50%*_pga_max_size）
(pga_aggreate_target影響_pga_max_size,_pga_max_size影響_smm_max_size)
有時候手動修改_pga_max_size后，如果要讓算法繼續(xù)執(zhí)行，需要reset下，否則不使用算法了.

改 pga_aggregate_target<500M
SQL> alter system set pga_aggregate_target=499m;

System altered.

SQL> startup force
ORACLE instance started.

NAME VALUE
------------------------------ -------------------------
DESCRIB
------------------------------------------------------------------------------------------------------------------------------------
_pga_max_size 209715200
Maximum size of the PGA memory for one process

SQL> /
Enter value for par: smm_max
old 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
new 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%smm_max%'

NAME VALUE
------------------------------ -------------------------
DESCRIB
------------------------------------------------------------------------------------------------------------------------------------
_smm_max_size 102195
maximum work area size in auto mode (serial)

SQL> select 102195/1024 from dual;

102195/1024
-----------
99.7998047 _smm_max_size=99.8m,_pga_max_size =200M

SQL> show parameter pga

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
pga_aggregate_target big integer 499M
SQL> select 499*0.2 from dual;

499*0.2
----------
99.8

SQL> select 0.4*499 from dual;

0.4*499
----------
199.6

分析 _pga_max_size >40%pga_aggregate_target ,所以_smm_max_size=20%*pga_aggregate_target =99.8M

手動改_pga_max_size為300M,pga_aggregate_target=501M
SQL> alter system set "_pga_max_size"=300M SCOPE=SPFILE;

System altered.

SQL> startup force;
ORACLE instance started.

NAME VALUE
------------------------------ -------------------------
DESCRIB
------------------------------------------------------------------------------------------------------------------------------------
_pga_max_size 314572800
Maximum size of the PGA memory for one process

SQL> /
Enter value for par: smm_max
old 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
new 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%smm_max%'

NAME VALUE
------------------------------ -------------------------
DESCRIB
------------------------------------------------------------------------------------------------------------------------------------
_smm_max_size 102604
maximum work area size in auto mode (serial)

SQL> show parameter pga

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
_pga_max_size big integer 300M
pga_aggregate_target big integer 501M
SQL>
SQL> select 102604/1024 from dual;

102604/1024
-----------
100.199219

SQL> select 0.2*501 from dual;

0.2*501
----------
100.2

分析
_pga_max_size>40%*pga_aggregate_target,
按算法 pga_aggregate_target>500M<1G,_smm_max_size =100MB(按pga_aggregate_target between 500m and 1000M ,_smm_max_size=100M),但實際還是按
_pga_max_size>40%*pga_aggregate_target,_smm_max_size=20%*pga_aggregate_target =100.2m

做一個極端的,_pga_max_size=600M,pga_aggregate_target=700M,如果按 pga_aggregate_target between 500m and 1000M 那么_smm_max_size=100M,實際會是這樣嗎?

SQL> alter system set "_pga_max_size"=600m;

System altered.

SQL> alter system set pga_aggregate_target=700m;

System altered.

SQL> startup force
ORACLE instance started.

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
_pga_max_size big integer 600M
pga_aggregate_target big integer 700M
SQL> set linesize 132
SQL> column name format a30
SQL> column value format a25
SQL> SELECT x.ksppinm NAME, y.ksppstvl VALUE, x.ksppdesc describ
2 FROM SYS.x$ksppi x, SYS.x$ksppcv y
3 WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
4
SQL>
SQL> /
Enter value for par: smm_max
old 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
new 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%smm_max%'

NAME VALUE
------------------------------ -------------------------
DESCRIB
------------------------------------------------------------------------------------------------------------------------------------
_smm_max_size 143360
maximum work area size in auto mode (serial)

可以看到_smm_max_size=140G沒有按,pga_aggregate_target>500M<1G時候應(yīng)該=100m,_pga_max_size>40%*pga_aggregate_target,而是按20%*pga_aggreget_target算的=140G了

設(shè)置_pga_max_size=199g,pga_aggregate_target=501g
SQL> alter system set "_pga_max_size"=199M SCOPE=SPFILE;

System altered.

SQL> startup force
ORACLE instance started.

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
_pga_max_size big integer 199M
pga_aggregate_target big integer 501M
SQL> set linesize 132
SQL> column name format a30
SQL> column value format a25
SQL> SELECT x.ksppinm NAME, y.ksppstvl VALUE, x.ksppdesc describ
2 FROM SYS.x$ksppi x, SYS.x$ksppcv y
3 WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
4
SQL> /
Enter value for par: smm_max
old 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
new 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%smm_max%'

NAME VALUE
------------------------------ -------------------------
DESCRIB
------------------------------------------------------------------------------------------------------------------------------------
_smm_max_size 101888
maximum work area size in auto mode (serial)

SQL> select 101888/1024 from dual;

101888/1024
-----------
99.5~~~~~~~~~~~~~~~

分析_pga_max_size<40%pga_aggregat_target,所以_smm_max_size=50%_pga_max_size

SQL> alter system set "_pga_max_size"=99M SCOPE=SPFILE;

System altered.

SQL> startup force
ORACLE instance started.

NAME VALUE
------------------------------ -------------------------
DESCRIB
------------------------------------------------------------------------------------------------------------------------------------
_pga_max_size 103809024
Maximum size of the PGA memory for one process

SQL> /
Enter value for par: smm_max
old 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
new 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%smm_max%'

NAME VALUE
------------------------------ -------------------------
DESCRIB
------------------------------------------------------------------------------------------------------------------------------------
_smm_max_size 50688
maximum work area size in auto mode (serial)

SQL> select 103809024/1024/1024 from dual
2 ;

103809024/1024/1024
-------------------
99

SQL> select 50688 /1024 from dual;

50688/1024
----------
49.5
_smm_max_size = 49.5

分析_pga_max_size<40%pga_aggregat_target,所以_smm_max_size=50%_pga_max_size

有文擋說_smm_max_size最大0.25GB,實際是這樣嗎
SQL> alter system set pga_aggregate_target=2g; 修改為2g

System altered.

SQL> startup force;
ORACLE instance started.

NAME VALUE
------------------------------ -------------------------
DESCRIB
------------------------------------------------------------------------------------------------------------------------------------
_pga_max_size 419430400
Maximum size of the PGA memory for one process

_pga_max_size =20%*pga_aggreaget_target=400m
SQL> /
Enter value for par: smm_max
old 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
new 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%smm_max%'

NAME VALUE
------------------------------ -------------------------
DESCRIB
------------------------------------------------------------------------------------------------------------------------------------
_smm_max_size 204800
maximum work area size in auto mode (serial)

_pga_max_size<40%pga_aggregate_target,所以_smm_max_size=50%*_pga_max_size=200m

文檔中當(dāng)pga_aggrgate_target >1G情況時,其實還是按上面的計算方式
_pga_max_size=20%*pga_aggregate_target
_smm_max_size=10%*pga_aggregate_target

一套負(fù)責(zé)的生產(chǎn)庫中pga (11g,11.1.0.7)
SQL> show parameter target

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
archive_lag_target integer 0
db_flashback_retention_target integer 1440
fast_start_io_target integer 0
fast_start_mttr_target integer 0
memory_max_target big integer 0
memory_target big integer 0 **********************沒開
SQL> show parameter pga

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
pga_aggregate_target big integer 30G
SQL> set linesize 132
SQL> column name format a30
SQL> column value format a25
SQL> SELECT x.ksppinm NAME, y.ksppstvl VALUE, x.ksppdesc describ
2 FROM SYS.x$ksppi x, SYS.x$ksppcv y
3 WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
4
SQL>
SQL> /
Enter value for par: pga_max
old 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
new 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%pga_max%'

NAME VALUE
------------------------------ -------------------------
DESCRIB
------------------------------------------------------------------------------------------------------------------------------------
_pga_max_size 2147483648
Maximum size of the PGA memory for one process

SQL> /
Enter value for par: smm_max
old 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
new 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%smm_max%'

可以看到 _smm_max_size早就超過了250M 到達(dá)了1G,這個數(shù)是根據(jù)_pga_max_size決定
當(dāng)pga_aggreate_size>1g時候,_pga_max_size=20%*pga_aggreate_size(pga_aggreate_size>10g時,_pga_max_size不變)
_pga_max_size=20%*10g<40%*pga_aggreaget_size,所以_smm_max_size=50%*_pga_max_size=1g

總結(jié)10g r2

PGA_AGGREATE_TARGET與_smm_max_size
pga_aggregate_target<=500MB,_smm_max_size=20%*pga_aggregate_target
pga_aggregate_target between 500m and 1000M ,_smm_max_size=100M
pga_aggregate_target between 1001m and 2.5g,_smm_max_size=10%*pga_aggregate_target

pga_aggregate_target,_pga_max_size 關(guān)系
_pga_max_size如果pga_aggregate_target<1g _pga_max_size=默認(rèn)200MB
_pga_max_size如果pga_aggregate_target>1g,_pga_max_size=20%*pga_aggregate_target(>5G不再變化)

實際到內(nèi)部
_smm_max_size為實際控制單個process使用pga上限,唯一可以相關(guān)他的參數(shù)是_pga_max_size,_pga_max_size被pga_aggregate_target相關(guān)
_pga_max_size<40%*pga_aggregate_target,_smm_max_size=50%*_pga_max_size，
其他時候（_pga_max_size>40%*pga_aggregate_target） _smm_max_size=20%PGA_AGGREGATe_TARGET

具體process可以使用的pga就是由_smm_max_size控制

> "_pga_max_size" is 200M by default.

That was true up to Oracle 10.1. Since 10.2 it is a dynamic parameter.

In 10.2 it is limited to 200M as long as pga_aggregate_target is smaller as 1GB.
When pga_aggregate_target is set to a larger value as 1GB then _pga_max_size= 20% of pga_aggregate_target .

> Is 350M of "pga_aggregate_target" effective even when "_pga_max_size" is 200M?
Yes it is still effective. The size of one work area (hash area, sort area) is not directly limited by _pga_max_size but by _smm_max_size (unit of this parameter is KBytes!). When you set pga_aggregate_target to 350M _smm_max_size should have a value like 71680 (71680KB => 70MB).

隨著版本的變化內(nèi)存管理也發(fā)生變化

11g內(nèi)存管理更加簡單了
只要設(shè)置memory_target=PGA+SGA這叫做amm特性，automatic memory management
設(shè)置后取代了pga_aggregate_target,sga_target,原理跟設(shè)置sga_target一樣，_pga_aggregate_target,_sga_target表示數(shù)據(jù)庫上次正常關(guān)閉時候內(nèi)存分配的樣子

oracle啟動時候會用 pga_aggregate_target,sga_target與_pga_aggregate_target,_sga_target,誰的值大用誰

SQL> show parameter target

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
archive_lag_target integer 0
db_flashback_retention_target integer 1440
fast_start_io_target integer 0
fast_start_mttr_target integer 0
memory_max_target big integer 476M
memory_target big integer 476M ****************************
pga_aggregate_target big integer 60M
sga_target big integer 0

SQL> set linesize 132
SQL> column name format a30
SQL> column value format a25
SQL> SELECT x.ksppinm NAME, y.ksppstvl VALUE, x.ksppdesc describ
2 FROM SYS.x$ksppi x, SYS.x$ksppcv y
3 WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
4
SQL>
SQL> /
Enter value for par: pga_aggrega
old 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
new 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%pga_aggrega%'

NAME VALUE
------------------------------ -------------------------
DESCRIB
------------------------------------------------------------------------------------------------------------------------------------
pga_aggregate_target 62914560
Target size for the aggregate PGA memory consumed by the instance

__pga_aggregate_target 150994944
Current target size for the aggregate PGA memory consumed

可以看到實際pga為150M
SQL> /
Enter value for par: pga_max
old 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%&par%'
new 3: WHERE x.indx = y.indx AND x.ksppinm LIKE '%pga_max%'

NAME

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oraclePGA管理(算法)

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