Oracle的db_name和instance_name

对于Oracle数据库来说，db_name和instance_name可以不同。
我们来看一下Oracle文档中对于db_name的定义:

DB_NAME必须是一个不超过8个字符的文本串.在数据库创建过程中,db_name被记录在数据文件，日志文件和控制文件中。如果数据库实例启动过程中参数文件中的db_name和控制文件中的数据库名称不一致，则数据库不能启动。

一个实例可以mount并打开任何数据库，但是同一时间一个实例只能打开一个数据库。
一个数据库可以被一个或多个实例所mount并打开（在OPS/RAC环境下，一个数据库可以被多个实例所打开）.

我们看一下我的数据库:

[oracle@jumper dbs]$ grep name initeygle.ora *.db_name='eygle' *.instance_name='eygle'

当前参数设置下的数据库:

SQL> select name from v$datafile; NAME ----------------------------------------------------- /opt/oracle/oradata/eygle/system01.dbf /opt/oracle/oradata/eygle/undotbs01.dbf /opt/oracle/oradata/eygle/users01.dbf /opt/oracle/oradata/eygle/eygle01.dbf SQL> show parameter db_name NAME TYPE VALUE ------------------------------------ ----------- ----------- db_name string eygle SQL> show parameter instance_name NAME TYPE VALUE ------------------------------------ ----------- ----------- instance_name string eygle SQL> create pfile from spfile; File created. SQL> exit Disconnected from Oracle9i Enterprise Edition Release 9.2.0.4.0 - Production With the Partitioning option JServer Release 9.2.0.4.0 - Production

我们创建一个新的pfile为julia这个新的实例使用:

[oracle@jumper oracle]$ cd $ORACLE_HOME/dbs [oracle@jumper dbs]$ cp initeygle.ora initjulia.ora [oracle@jumper dbs]$ ll init* -rw-r--r-- 1 oracle dba 982 Jul 25 14:03 initeygle.ora -rw-r--r-- 1 oracle dba 982 Jul 25 14:04 initjulia.ora -rw-r--r-- 1 oracle dba 8385 Mar 9 2002 init.ora

修改这个文件更改:
instance_name = julia

修改后的参数设置:

[oracle@jumper dbs]$ grep name initjulia.ora *.db_name='eygle' *.instance_name='julia'

然后我们启动实例名称为julia的instance:

[oracle@jumper dbs]$ export ORACLE_SID=julia [oracle@jumper dbs]$ sqlplus "/ as sysdba" SQL*Plus: Release 9.2.0.4.0 - Production on Tue Jul 25 14:04:15 2006 Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved. Connected to an idle instance. SQL> startup mount; ORACLE instance started. Total System Global Area 139531744 bytes Fixed Size 452064 bytes Variable Size 121634816 bytes Database Buffers 16777216 bytes Redo Buffers 667648 bytes ORA-01102: cannot mount database in EXCLUSIVE mode SQL> exit Disconnected from Oracle9i Enterprise Edition Release 9.2.0.4.0 - Production With the Partitioning option JServer Release 9.2.0.4.0 - Production

注意，此时试图加载数据库时出现错误，因为当前数据库被另外一个实例(instance)加载。在非并行模式(Ops/RAC)下，一个数据库同时只能被一个实例加载。

此时已经启动了两个数据库实例，从后台进程可以看出：

[oracle@jumper dbs]$ ps -ef|grep ora oracle 27321 1 0 Jul14 ? 00:00:00 ora_pmon_eygle oracle 27323 1 0 Jul14 ? 00:00:00 ora_dbw0_eygle oracle 27325 1 0 Jul14 ? 00:00:00 ora_lgwr_eygle oracle 27327 1 0 Jul14 ? 00:00:00 ora_ckpt_eygle oracle 27329 1 0 Jul14 ? 00:00:32 ora_smon_eygle oracle 27331 1 0 Jul14 ? 00:00:00 ora_reco_eygle oracle 27333 1 0 Jul14 ? 00:00:00 ora_cjq0_eygle root 15388 656 0 14:02 ? 00:00:00 sshd: oracle [priv] oracle 15390 15388 0 14:02 ? 00:00:00 sshd: oracle@pts/2 oracle 15391 15390 0 14:02 pts/2 00:00:00 -bash oracle 15445 1 0 14:04 ? 00:00:00 ora_pmon_julia oracle 15447 1 0 14:04 ? 00:00:00 ora_dbw0_julia oracle 15449 1 0 14:04 ? 00:00:00 ora_lgwr_julia oracle 15451 1 0 14:04 ? 00:00:00 ora_ckpt_julia oracle 15453 1 0 14:04 ? 00:00:00 ora_smon_julia oracle 15455 1 0 14:04 ? 00:00:00 ora_reco_julia oracle 15457 1 0 14:04 ? 00:00:00 ora_cjq0_julia oracle 15459 15391 0 14:04 pts/2 00:00:00 ps -ef oracle 15460 15391 0 14:04 pts/2 00:00:00 grep ora

我们关闭eygle这个数据库实例:

[oracle@jumper dbs]$ export ORACLE_SID=eygle [oracle@jumper dbs]$ sqlplus "/ as sysdba" SQL*Plus: Release 9.2.0.4.0 - Production on Tue Jul 25 14:04:39 2006 Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved. Connected to: Oracle9i Enterprise Edition Release 9.2.0.4.0 - Production With the Partitioning option JServer Release 9.2.0.4.0 - Production SQL> shutdown immediate; Database closed. Database dismounted. ORACLE instance shut down. SQL> exit Disconnected from Oracle9i Enterprise Edition Release 9.2.0.4.0 - Production With the Partitioning option JServer Release 9.2.0.4.0 - Production

此时就可以通过实例julia加载并打开db_name=eygle的数据库了:

[oracle@jumper dbs]$ export ORACLE_SID=julia [oracle@jumper dbs]$ sqlplus "/ as sysdba" SQL*Plus: Release 9.2.0.4.0 - Production on Tue Jul 25 14:05:06 2006 Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved. Connected to: Oracle9i Enterprise Edition Release 9.2.0.4.0 - Production With the Partitioning option JServer Release 9.2.0.4.0 - Production SQL> alter database mount; alter database mount * ERROR at line 1: ORA-01990: error opening password file '/opt/oracle/product/9.2.0/dbs/orapw' ORA-27037: unable to obtain file status Linux Error: 2: No such file or directory Additional information: 3 SQL> alter database open; Database altered. SQL> select name from v$datafile; NAME ---------------------------------------------------------------------------- /opt/oracle/oradata/eygle/system01.dbf /opt/oracle/oradata/eygle/undotbs01.dbf /opt/oracle/oradata/eygle/users01.dbf /opt/oracle/oradata/eygle/eygle01.dbf SQL> ! ps -ef|grep ora root 15388 656 0 14:02 ? 00:00:00 sshd: oracle [priv] oracle 15390 15388 0 14:02 ? 00:00:00 sshd: oracle@pts/2 oracle 15391 15390 0 14:02 pts/2 00:00:00 -bash oracle 15445 1 0 14:04 ? 00:00:00 ora_pmon_julia oracle 15447 1 0 14:04 ? 00:00:00 ora_dbw0_julia oracle 15449 1 0 14:04 ? 00:00:00 ora_lgwr_julia oracle 15451 1 0 14:04 ? 00:00:00 ora_ckpt_julia oracle 15453 1 0 14:04 ? 00:00:00 ora_smon_julia oracle 15455 1 0 14:04 ? 00:00:00 ora_reco_julia oracle 15457 1 0 14:04 ? 00:00:00 ora_cjq0_julia oracle 15513 15391 0 14:05 pts/2 00:00:00 sqlplus oracle 15514 15513 3 14:05 ? 00:00:01 oraclejulia (DESCRIPTION=(LOCAL=YES)(ADDRESS=(PROTOCOL=beq))) oracle 15515 15513 0 14:05 pts/2 00:00:00 /bin/bash -c ps -ef|grep ora oracle 15516 15515 0 14:05 pts/2 00:00:00 ps -ef SQL> show parameter instance_name NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ instance_name string julia SQL> show parameter db_name NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ db_name string eygle

我们再看看如果参数文件中的db_name和控制文件中的db_name不一致会出现什么错误.
修改参数db_name:

[oracle@jumper dbs]$ grep name initjulia.ora *.db_name='julia' *.instance_name='julia'

在启动过程中，我们看到，在mount阶段，数据库会对参数文件和控制文件进行比较，如果两者记录的db_name不一致，则数据库无法启动:

SQL> startup nomount; ORACLE instance started. Total System Global Area 139531744 bytes Fixed Size 452064 bytes Variable Size 121634816 bytes Database Buffers 16777216 bytes Redo Buffers 667648 bytes SQL> alter database mount; alter database mount * ERROR at line 1: ORA-01103: database name 'EYGLE' in controlfile is not 'JULIA'

另外的一个区别是，db_name通常限制在8个字符之内；instance_name最多应该支持21个字符。通常我们都是设置db_name和instance_name一致。需要注意的是如果db_name设置过长，则会被Oracle截断为8个字符，而instance_name仍然会保留在21个字符之内，如果你的环境变量设置的instance_name=db_name，则启动时就会出现问题，你需要重建pfile/spfile并且修改环境变量才能启动实例，加载数据库。