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v$log 中看到的online redo log的三种状态

原创 Linux操作系统 作者:tolywang 时间:2007-10-13 00:00:00 0 删除 编辑
UNUSED - The online redo log has never been written to. This is the state of a redo log that was just added, or just after a RESETLOGS, when it is not the current redo log.

CURRENT - This is the current redo log. This implies that the redo log is active. The redo log could be open or closed.

ACTIVE - The log is active but is not the current log. It is needed for crash recovery. It may be in use for block recovery. It might or might not be archived.

CLEARING - The log is being re-created as an empty log after an ALTER DATABASE CLEAR LOGFILE statement. After the log is cleared, the status changes to UNUSED.

CLEARING_CURRENT - The current log is being cleared of a closed thread. The log can stay in this status if there is some failure in the switch such as an I/O error writing the new log header.

INACTIVE - The log is no longer needed for instance recovery. It may be in use for media recovery. It might or might not be archived.


而checkpoint有个规则,如下,会保证处于active的日志组不多于1个。
The checkpoint position will never lag the end of the log data by more than one log file since the longest the span can be is 90% of the smallest log。

有的情况下,可以看到存在多个active的日志组,原因可能是dbwr写的太慢。

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