在线日志状态含义

1.UNUSED:表示在线日志没被用过。一般是刚刚加上，或者RESETLOGS
2.CURRENT：当前的重做日志。
3.ACTIVE：日志是激活的，但不是当前的日志。当进行灾难恢复的时候，是需要的。它可能正在用于块恢复。它可能也可能没有被归档。
4.CLEARING：日志文件被重建。完成之后是UNUSED状态。
5.CLEARING_CURRENT:当前日志被清除。
6.INACTIVE：日志对于实例恢复已经无用。可能用于块恢复。可能已经，也可能没有被归档。

一直理解的是错误的。原来这个状态，跟归档与否是没有关系的。。。

引自：reference 11gR2 E40402-18  P980

■UNUSED - 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 - Current redo log. This implies that the redo log is active.
The redo log could be open or closed.
■ ACTIVE - Log is active but is not the current log. It is needed for crash
recovery. It may be in use for block recovery. It may or may not be
archived.
■ CLEARING - 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 - 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 - Log is no longer needed for instance recovery. It may be in
use for media recovery. It may or may not be archived.