查看Oracle的redo日志切换频率：
单位：分钟
第一种：
select * from v$log a where a.THREAD# = 1 ;
set line 200
select b.SEQUENCE#, b.FIRST_TIME,a.SEQUENCE#,a.FIRST_TIME,round(((a.FIRST_TIME-b.FIRST_TIME)*24)*60,2) from v$log_history a, v$log_history b where a.SEQUENCE#=b.SEQUENCE#+1 and b.THREAD#=1 order by a.SEQUENCE# desc;
第二种：
set line 200
select sequence#,first_time,nexttime,round(((first_time-nexttime)*24)*60,2) diff from (select sequence#,first_time,lag(first_time) over(order by sequence#) nexttime from v$log_history where thread#=1) order by sequence# desc;
看你的redo日志大小。 Oracle给的建议是一般15-20分钟左右，要根据数据量来判断，最长时间（单位时间内数据量最少）维持在25-30分钟，最好不要超过30分钟。最短时间（单位时间内数据量最大），保持在10分钟以上。
SELECT trunc(first_time) "Date", to_char(first_time, 'Dy') "Day", count(1) "Total", SUM(decode(to_char(first_time, 'hh24'),'00',1,0)) "h0", SUM(decode(to_char(first_time, 'hh24'),'01',1,0)) "h1", SUM(decode(to_char(first_time, 'hh24'),'02',1,0)) "h2", SUM(decode(to_char(first_time, 'hh24'),'03',1,0)) "h3", SUM(decode(to_char(first_time, 'hh24'),'04',1,0)) "h4", SUM(decode(to_char(first_time, 'hh24'),'05',1,0)) "h5", SUM(decode(to_char(first_time, 'hh24'),'06',1,0)) "h6", SUM(decode(to_char(first_time, 'hh24'),'07',1,0)) "h7", SUM(decode(to_char(first_time, 'hh24'),'08',1,0)) "h8", SUM(decode(to_char(first_time, 'hh24'),'09',1,0)) "h9", SUM(decode(to_char(first_time, 'hh24'),'10',1,0)) "h10", SUM(decode(to_char(first_time, 'hh24'),'11',1,0)) "h11", SUM(decode(to_char(first_time, 'hh24'),'12',1,0)) "h12", SUM(decode(to_char(first_time, 'hh24'),'13',1,0)) "h13", SUM(decode(to_char(first_time, 'hh24'),'14',1,0)) "h14", SUM(decode(to_char(first_time, 'hh24'),'15',1,0)) "h15", SUM(decode(to_char(first_time, 'hh24'),'16',1,0)) "h16", SUM(decode(to_char(first_time, 'hh24'),'17',1,0)) "h17", SUM(decode(to_char(first_time, 'hh24'),'18',1,0)) "h18", SUM(decode(to_char(first_time, 'hh24'),'19',1,0)) "h19", SUM(decode(to_char(first_time, 'hh24'),'20',1,0)) "h20", SUM(decode(to_char(first_time, 'hh24'),'21',1,0)) "h21", SUM(decode(to_char(first_time, 'hh24'),'22',1,0)) "h22", SUM(decode(to_char(first_time, 'hh24'),'23',1,0)) "h23" FROM V$log_history group by trunc(first_time), to_char(first_time, 'Dy') Order by 1
