linux操作系统下,oracle db 11g中增大memory_max_target和memory_target应该注意的：

[oracle@hosta ~]$ sqlplus / as sysdba

SQL*Plus: Release 11.1.0.7.0 - Production on Tue Jul 14 01:12:24 2015

Copyright (c) 1982, 2008, Oracle.  All rights reserved.


Connected to:
Oracle Database 11g Enterprise Edition Release 11.1.0.7.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> show parameter inst

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
active_instance_count                integer
cluster_database_instances           integer     1
instance_groups                      string
instance_name                        string      orcl
instance_number                      integer     0
instance_type                        string      RDBMS
open_links_per_instance              integer     4
parallel_instance_group              string
parallel_server_instances            integer     1
SQL> show parameter mem

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
hi_shared_memory_address             integer     0
memory_max_target                    big integer 404M
memory_target                        big integer 404M
shared_memory_address                integer     0
SQL> alter system set memory_max_target=2048M scope=spfile;

System altered.

SQL> alter system set memory_target =2048M scope=spfile;

System altered.

SQL> show parameter memory


NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
hi_shared_memory_address             integer     0
memory_max_target                    big integer 404M
memory_target                        big integer 404M
shared_memory_address                integer     0
SQL> SQL> 
SQL> show spparameter memory

SID      NAME                          TYPE        VALUE
-------- ----------------------------- ----------- ----------------------------
*        hi_shared_memory_address      integer
*        memory_max_target             big integer 2G
*        memory_target                 big integer 2G
*        shared_memory_address         integer
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORA-00845: MEMORY_TARGET not supported on this system
SQL> 

此时的alert日志如下：

Tue Jul 14 01:15:13 2015
Starting ORACLE instance (normal)
WARNING: You are trying to use the MEMORY_TARGET feature. 
This feature requires the /dev/shm file system to be mounted for at least 2046820352 bytes. 
/dev/shm is either not mounted or is mounted with available space less than this size. 
Please fix this so that MEMORY_TARGET can work as expected. 
Current available is 1595297792 and used is 0 bytes.
memory_target needs larger /dev/shm
Tue Jul 14 01:21:45 2015
Starting ORACLE instance (normal)
LICENSE_MAX_SESSION = 0
LICENSE_SESSIONS_WARNING = 0
Picked latch-free SCN scheme 2
Using LOG_ARCHIVE_DEST_10 parameter default value as USE_DB_RECOVERY_FILE_DEST
Autotune of undo retention is turned on.
IMODE=BR
ILAT =18
LICENSE_MAX_USERS = 0
SYS auditing is disabled
Starting up ORACLE RDBMS Version: 11.1.0.7.0.
Using parameter settings in server-side spfile /u01/app/oracle/product/11.1.0/db_1/dbs/spfileorcl.ora
System parameters with non-default values:
  processes                = 150
  memory_target            = 2G
  memory_max_target        = 2G
  control_files            = "/u01/app/oracle/oradata/orcl/control01.ctl"
  control_files            = "/u01/app/oracle/oradata/orcl/control02.ctl"
  control_files            = "/u01/app/oracle/oradata/orcl/control03.ctl"

参考文章：

ORA-00845 - Which value for /dev/shm is needed to startup database without ORA-00845 (文档 ID 1399209.1)
ORA-00845 Raised When Starting Instance (文档 ID 465048.1)