12c新特性之PGA_AGGREGATE_LIMIT

11g

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[root@roidb1 ~]# su - oracle
<roidb1:orcl1:/home/oracle>$sqlplus / as sysdba

SQL*Plus: Release 11.2.0.4.0 Production on Wed Dec 13 21:40:51 2017

Copyright (c) 1982, 2013, Oracle.  All rights reserved.

Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, Real Application Clusters, Automatic Storage Management, OLAP,
Data Mining and Real Application Testing options

SQL> show parameter pga;

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
pga_aggregate_target                 big integer 0
SQL> 

12c

[root@rac01 ~]# su - oracle
Last login: Fri Dec  8 16:09:27 CST 2017 on pts/0
<rac01:orcl1:/home/oracle>$sqlplus / as sysdba

SQL*Plus: Release 12.1.0.2.0 Production on Wed Dec 13 21:33:48 2017

Copyright (c) 1982, 2014, Oracle.  All rights reserved.

Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, Real Application Clusters, Automatic Storage Management, OLAP,
Advanced Analytics and Real Application Testing options

SYS@orcl1> show parameter pga;

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
pga_aggregate_limit                  big integer 2G
pga_aggregate_target                 big integer 390M
SYS@orcl1> 

--官方解釋
Property    Description
Parameter type

Big integer

Syntax

PGA_AGGREGATE_LIMIT = integer [K | M | G]

Default value

By default, PGA_AGGREGATE_LIMIT is set to the greater of 2 GB, 200% of PGA_AGGREGATE_TARGET, and 3 MB times the PROCESSES parameter. It will be set below 200% of PGA_AGGREGATE_TARGET if it is larger than 90% of the physical memory size minus the total SGA size, but not below 100% of PGA_AGGREGATE_TARGET.

Modifiable

ALTER SYSTEM

Modifiable in a PDB

No

Range of values

Oracle recommends that you do not set PGA_AGGREGATE_LIMIT below its default value. PGA_AGGREGATE_LIMIT cannot be set below its default value except in a text initialization parameter file (pfile) or binary server parameter file (spfile). If a value of 0 is specified, it means there is no limit to the aggregate PGA memory consumed by the instance.

Basic

No

PGA_AGGREGATE_LIMIT specifies a limit on the aggregate PGA memory consumed by the instance.

There is no difference in behavior between PGA_AGGREGATE_LIMIT being explicitly set or being set to the default.

SYS@orcl1> show parameter pga;

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
pga_aggregate_limit                  big integer 2G
pga_aggregate_target                 big integer 390M
SYS@orcl1> alter system set pga_aggregate_limit=3G  --動(dòng)態(tài)修改

System altered.

SYS@orcl1> show parameter pga;

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
pga_aggregate_limit                  big integer 3G
pga_aggregate_target                 big integer 390M
SYS@orcl1> alter system set pga_aggregate_limit=350m;
alter system set pga_aggregate_limit=350m
*
ERROR at line 1:
ORA-02097: parameter cannot be modified because specified value is invalid
ORA-00093: pga_aggregate_limit must be between 2048M and 100000G
--大小不能小于2G
SYS@orcl1> alter system set pga_aggregate_limit=2048m;

System altered.

SYS@orcl1> alter system set pga_aggregate_limit=2047m;
alter system set pga_aggregate_limit=2047m
*
ERROR at line 1:
ORA-02097: parameter cannot be modified because specified value is invalid
ORA-00093: pga_aggregate_limit must be between 2048M and 100000G

SYS@orcl1> 

在 Oracle 12c R1 之前，沒有選項(xiàng)可以用來限制和控制 PGA 的大小。雖然你設(shè)置某個(gè)大小為 PGA_AGGREGATE_TARGET 的初始參數(shù)，Oracle 會(huì)根據(jù)工作負(fù)載和需求來動(dòng)態(tài)地增大或減小 PGA 的大小。而在 12c 中，你可以通過開啟自動(dòng) PGA 管理來對(duì) PGA 設(shè)定硬性限制，這需要對(duì) PGA_AGGREGATE_LIMIT 參數(shù)進(jìn)行設(shè)置。因此，你現(xiàn)在可以通過設(shè)置新的參數(shù)來對(duì) PGA 設(shè)定硬性限制以避免過度使用 PGA。

新聞名稱：12c新特性之PGA_AGGREGATE_LIMIT
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