Oracle体系结构及备份（十二）——bg-smon

一 什么是SMON进程

 

        The systemmonitor performs recovery when a failed instance starts up again. In an OracleReal Application Clusters database, the SMON process of one instance canperform instance recovery for other instances that have failed. SMON alsocleans up temporary segments that are no longer in use and recovers deadtransactions skipped during system failure and instance recovery because offile-read or offline errors. These transactions are eventually recovered bySMON when the tablespace or file is brought back online.

 

        作用：

        实例恢复

                前滚所有重做日志中的改变

                打开数据库为了用户能访问

                回滚没有提交的事务

        接合自由的空间（Coalesce every three secons）

        释放临时表空间（Deal Located）

 

二 操作示例

SQL> startup force;
ORACLE instance started.

Total System Global Area  838860800 bytes
Fixed Size		    1222192 bytes
Variable Size		  775948752 bytes
Database Buffers	   58720256 bytes
Redo Buffers		    2969600 bytes
Database mounted.
Database opened.
SQL> startup force mount;
ORACLE instance started.

Total System Global Area  838860800 bytes
Fixed Size		    1222192 bytes
Variable Size		  775948752 bytes
Database Buffers	   58720256 bytes
Redo Buffers		    2969600 bytes
Database mounted.
--出现此问题：关闭数据库，然后重启
SQL> alter database archivelog;
alter database archivelog
*
ERROR at line 1:
ORA-00265: instance recovery required, cannot set ARCHIVELOG mode

SQL> shutdown immediate;
ORA-01109: database not open


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

Total System Global Area  838860800 bytes
Fixed Size		    1222192 bytes
Variable Size		  775948752 bytes
Database Buffers	   58720256 bytes
Redo Buffers		    2969600 bytes
Database mounted.
Database opened.
SQL> shutdown mount;
SP2-0717: illegal SHUTDOWN option
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount;
ORACLE instance started.

Total System Global Area  838860800 bytes
Fixed Size		    1222192 bytes
Variable Size		  775948752 bytes
Database Buffers	   58720256 bytes
Redo Buffers		    2969600 bytes
Database mounted.

SQL> alter database noarchivelog;

Database altered.

SQL> alter database open;

Database altered.

三 总结

        1. SMON：系统监控进程，静态注册监听

        2.SMON作用：实例恢复、接合自由的空间（Coalesceevery three secons）、

释放临时表空间（Deal Located）

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  By Larry Wen

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