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2024年4月28日发(作者：安卓download下载官网)
alter system switch logfile
和alter system archive log current的区别
alter system switch logfile 是强制日志切换，不一定就归档当前的重做日志文件（若自动
归档打开，就归档前的重做日志，若自动归档没有打开，就不归档当前重做日志。）
alter system archive log current 是归档当前的重做日志文件，不管自动归档有没有打都
归档。
这条命令导致Oracle切换到一个新的日志文件，当前联机重做日志文件归档， 并且Oracle归档所有
未被归档的重做日志文件。
主要的区别在于:
ALTER SYSTEM SWITCH LOGFILE对单实例数据库或RAC中的当前实例执行日志切换;
而ALTER SYSTEM ARCHIVE LOG CURRENT会对数据库中的所有实例执行日志切换。
为什么执行热备后要执行alter system archive log current 这个语句，看到很多脚本都是
这样写的。是不是必须的？
一般的RMAN脚本都是这样写的，因为RMAN是可以备份归档日志的。
alter system archive log current 这样后就可以将所有的归档都备份出来了。这样做是为
了保证数据的完整和一致。
ALTER SYSTEM SWITCH LOGFILE ;
SWITCH LOGFILE Clause
TheSWITCHLOGFILEclause lets you explicitly force Oracle to begin writing to
a new redo log file group, regardless of whether the files in the current redo
log file group are full. When you force a log switch, Oracle begins to perform.
a checkpoint but returns control to you immediately rather than when the
checkpoint is complete. To use this clause, your instance must have the database
open.
ALTER SYSTEM ARCHIVE LOG CURRENT ;
CURRENT Clause
Specify CURRENT to manually archive the current redo log file group of the
specified thread, forcing a log switch. If you omit the THREAD parameter, then
Oracle archives all redo log file groups from all enabled threads, including
logs previous to current logs. You can specifyCURRENTonly when the database
is open.
ALTER SYSTEM ARCHIVE LOG CURRENT NOSWITCH;
NOSWITCH
SpecifyNOSWITCHif you want to manually archive the current redo log file group
without forcing a log switch. This setting is used primarily with standby
databases to prevent data divergence when the primary database shuts down.
Divergence implies the possibility of data loss in case of primary database
failure.
You can use theNOSWITCHclause only when your instance has the database mounted
but not open. If the database is open, then this operation closes the database
automatically. You must then manually shut down the database before you can
reopen it
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