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12c新特性之PGA_AGGREGATE_LIMIT
11g
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[root@roidb1 ~]# su - 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
$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(méi)有選項(xiàng)可以用來(lái)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(lái)動(dòng)態(tài)地增大或減小 PGA 的大小。而在 12c 中，你可以通過(guò)開(kāi)啟自動(dòng) PGA 管理來(lái)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(guò)設(shè)置新的參數(shù)來(lái)對(duì) PGA 設(shè)定硬性限制以避免過(guò)度使用 PGA。
當(dāng)前名稱：12c新特性之PGA_AGGREGATE_LIMIT
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