oracle数据库服务器（内存减小导致Oracle启动不了，解决方法）

原因：由于机器使用阿里云服务器，初期内存较大，所以选择中途降配，由8G减少到4G，降配完成后，数据库无法正常启动，报以下错误
ORA-00845: MEMORY_TARGET not supported on this system
经过查资料了解其原理后
发现：
原因可能：ORACLE MEMORY_TARGET参数设置超过了oracle服务器本身内存、或超过了现在服务器空闲内存（就是oracle启动时无法获取设置的内存），或者 超过了/dev/shm的大小/. 这些都有可能造成以上错误、

问题确认：
确认为oracle MEMORY_TARGET参数设置SGA大于操作系统的空闲内存，超过了/dev/shm的大小
解决：
修改MEMORY_TARGET的值为合适的范围之内（如果是正式环境切oracle需要设置MEMORY_TARGET的内存，需要增加服务器内存，本初不讨论）1.备份现有spfile文件

cp  init.ora.715201510237  init.ora.715201510237_bak

2.使用spfile创建pfile（spfile为二进制文本，不可直接修改），修改pfile后，重新生成spfile

SQL> create pfile from spfile;
File created.

修改pfile参数*.memory_target=104857600(此处的值小于 操作系统的空闲内存，小于/dev/shm的大小)

SQL> create spfile from pfile;
File created.
确认后，启动oracle

3，如果以上完成后，还无法正常startup,

SQL> startup pfile=/app/oracle/admin/orcl/pfile/init.ora.103201271612
SQL> alter system set memory_max_target=1258M scope=both;
alter system set memory_max_target=1258200M scope=both
*
ERROR at line 1:
ORA-02095: specified initialization parameter cannot be modified

SQL> alter system set memory_max_target=1258M scope=spfile;
alter system set memory_max_target=1258M scope=spfile
*
ERROR at line 1:
ORA-32001: write to SPFILE requested but no SPFILE is in use//spfile文件可能不存在
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down

SQL> startup nomount
ORA-01078: failure in processing system parameters
LRM-00109: could not open parameter file '/app/oracle/product/11.2.0/dbhome_2/dbs/initorcl.ora'
#------------------------------spfile不存在

#-----------------------------spfile位置：$ORACLE_HOME/dbs/init[ORACLE_SID].ora

#-----------------------------名字格式为:initORACLE_SID.ora

[oracle@h1 dbhome_2]$ cd /app/oracle/admin/orcl/pfile/
[oracle@h1 pfile]$ ls
init.ora.103201271612

[oracle@h1 pfile]$echo $ORACLE_SID

orcl

#-------------------查看环境变量$ORACLE_SID

[oracle@h1 pfile]$ cp init.ora.103201271612 /app/oracle/product/11.2.0/dbhome_2/dbs

[oracle@h1 pfile]$ cd /app/oracle/product/11.2.0/dbhome_2/dbs

[oracle@h1 dbs]$ mv init.ora.103201271612  initorcl.ora

#------------------------------更改名字格式为:initORACLE_SID.ora

4.mount数据库

[oracle@h1 dbs]$ sqlplus "/as SYSDBA"

SQL*Plus: Release 11.2.0.1.0 Production on Sun Nov 4 16:59:09 2012

Copyright (c) 1982, 2009, Oracle.  All rights reserved.

Connected to an idle instance.

SQL> startup mount
ORACLE instance started.

Total System Global Area 1219260416 bytes
Fixed Size                  2212856 bytes
Variable Size            738200584 bytes
Database Buffers          469762048 bytes
Redo Buffers                9084928 bytes
Database mounted.
SQL>

SQL> show parameter memory_target;

NAME                                TYPE        VALUE
------------------------------------ ----------- ------------------------------
memory_target                        big integer 1168M
SQL> show parameter memory_max_target;

NAME                                TYPE        VALUE
------------------------------------ ----------- ------------------------------
memory_max_target                    big integer 1168M
SQL>
SQL>  alter system set memory_max_target=1G scope=spfile;
alter system set memory_max_target=1G scope=spfile
*
ERROR at line 1:
ORA-32001: write to SPFILE requested but no SPFILE is in use

SQL> show parameter spfile;

NAME                                TYPE        VALUE
------------------------------------ ----------- ------------------------------
spfile                              string

#------------------重建spfile
SQL> create spfile from pfile;

File created.

SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL>  startup
ORACLE instance started.

Total System Global Area 1219260416 bytes
Fixed Size                  2212856 bytes
Variable Size            738200584 bytes
Database Buffers          469762048 bytes
Redo Buffers                9084928 bytes
Database mounted.
Database opened.
SQL> show parameter spfile;

NAME                                TYPE        VALUE
------------------------------------ ----------- ------------------------------
spfile                              string      /app/oracle/product/11.2.0/dbh
ome_2/dbs/spfileorcl.ora

SQL> alter system set memory_max_target=1G scope=spfile;

System altered.

SQL> alter system set memory_target=1G scope=both;

System altered.

SQL> alter system set memory_max_target=1332M scope=both;
alter system set memory_max_target=1332M scope=both
*
ERROR at line 1:
ORA-02095: specified initialization parameter cannot be modified

SQL> alter system set memory_max_target=1332M scope=spfile;

System altered.

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

SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.

Total System Global Area 1402982400 bytes
Fixed Size                  2213296 bytes
Variable Size            922749520 bytes
Database Buffers          469762048 bytes
Redo Buffers                8257536 bytes
Database mounted.
Database opened.
SQL> show parameter memory_max_target;

NAME                                TYPE        VALUE
------------------------------------ ----------- ------------------------------
memory_max_target                    big integer 1344M

SQL> show parameter memory_target;

NAME                                TYPE        VALUE
------------------------------------ ----------- ------------------------------
memory_target                        big integer 1G
SQL>
-----------------------finish

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