【DB笔试面试746】在O中，“...SWITCH LOGFILE”与“... ARCHIVE LOG CURRENT”区别

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发布于 2020-02-24 10:32:24

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发布于 2020-02-24 10:32:24

文章被收录于专栏：小麦苗的DB宝专栏

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题目部分

在Oracle中，RAC环境下“ALTER SYSTEM SWITCH LOGFILE;”与“ALTER SYSTEM ARCHIVE LOG CURRENT;”有什么区别？

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答案部分

“ALTER SYSTEM SWITCH LOGFILE;”仅对当前发布节点上的对应Redo Thread进行日志切换并归档。“ALTER SYSTEM ARCHIVE LOG CURRENT;”对集群内所有节点实例上的Redo Thread进行切换并归档（在节点实例可用情况下，分别归档到各节点主机的归档目的地，当节点不可用时候，该线程日志归档到命令发布节点的归档目的地）。

当然，命令“ALTER SYSTEM ARCHIVE LOG CURRENT;”对单实例的数据库也是起作用的，使用这个命令还可以对RAC环境中的指定实例进行日志切换：

alter system archive log instance 'lhrracdb2' current;

需要注意的是，命令“ALTER SYSTEM ARCHIVE LOG CURRENT;”对于非归档模式的数据库只能归档非当前Redo日志组，而对于归档模式的数据库则没有该限制，否则会报错：

SYS@lhrrac11> ALTER SYSTEM ARCHIVE LOG CURRENT;
ALTER SYSTEM ARCHIVE LOG CURRENT
*
ERROR at line 1:
ORA-00258: manual archiving in NOARCHIVELOG mode must identify log

SYS@lhrrac11> ALTER SYSTEM ARCHIVE LOG thread 1   sequence 14;

System altered.

SYS@lhrrac11> ALTER SYSTEM ARCHIVE LOG thread 1   sequence 15;
ALTER SYSTEM ARCHIVE LOG thread 1   sequence 15
*
ERROR at line 1:
ORA-00259: log 1 of open instance lhrrac11 (thread 1) is the current log, cannot archive

SYS@lhrrac11> ALTER SYSTEM ARCHIVE LOG thread 2   sequence 13 ;

System altered.

SYS@lhrrac11> exit
Disconnected from Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
With the Partitioning, Real Application Clusters, Automatic Storage Management, OLAP,
Data Mining and Real Application Testing options
[oracle@raclhr-11gR2-N1 ~]$ oerr ora 258
00258, 00000, "manual archiving in NOARCHIVELOG mode must identify log"
// *Cause: The database is in NOARCHIVELOG mode and a command to manually
//          archive a log did not specify the log explicitly by sequence
//          number, group number or filename.
// *Action: Specify log by filename, by group number or by thread and
//          sequence number.

最后提一下与日志相关的发出检查点操作的命令，在RAC数据库中也有所不同，以前的“alter system checkpoint;”与“alter system checkpoint global;”命令是等价的，将在所有数据库实例中触发检查点操作。如果想要在当前实例触发检查点，那么需要对命令稍作修改：