查看Oracle的redo日志切换频率

　　两个sql，原理是一样的，第二个用到了统计函数。

　　时间单位：分钟

　　select * from v$log

　　where a.THREAD# = 1

　　select b.SEQUENCE#, b.FIRST_TIME,

　　a.SEQUENCE#, a.FIRST_TIME,

　　round(((a.FIRST_TIME-b.FIRST_TIME)*24)*60,2)

　　from v$log_history a, v$log_history b

　　where a.SEQUENCE# = b.SEQUENCE#+1

　　and b.THREAD#=1

　　order by a.SEQUENCE# desc

　　select sequence#,first_time,nexttime,round(((first_time-nexttime)*24)*60,2) diff

　　from (

　　select sequence#,first_time, lag(first_time) over(order by sequence#) nexttime

　　from v$log_history

　　where thread#=1

　　) order by sequence# desc