Redo Log Switches at their Peak

One of our customers was having extreme performance issues with their Oracle database. During my investigations I found they had 215 redo log switches per hour. This means a 3.65 log switches per minute or a redo log switch every 16.7 seconds.

Although this was not the only reason of performance issues but this was certainly one of the causes. The redo log files were sized pretty small and the poor database was spending most of its time switch the redo log files.

Here’s a screenshot for you guys:

Below is the query I use to find redo log switches. This query lists redo log switches per hour for the last seven days.

column day format a10
column Switches_per_day format 9999
column 00 format 999
column 01 format 999
column 02 format 999
column 03 format 999
column 04 format 999
column 05 format 999
column 06 format 999
column 07 format 999
column 08 format 999
column 09 format 999
column 10 format 999
column 11 format 999
column 12 format 999
column 13 format 999
column 14 format 999
column 15 format 999
column 16 format 999
column 17 format 999
column 18 format 999
column 19 format 999
column 20 format 999
column 21 format 999
column 22 format 999
column 23 format 999

select to_char(first_time,'DD-MON') day,
sum(decode(to_char(first_time,'hh24'),'00',1,0)) "00",
sum(decode(to_char(first_time,'hh24'),'01',1,0)) "01",
sum(decode(to_char(first_time,'hh24'),'02',1,0)) "02",
sum(decode(to_char(first_time,'hh24'),'03',1,0)) "03",
sum(decode(to_char(first_time,'hh24'),'04',1,0)) "04",
sum(decode(to_char(first_time,'hh24'),'05',1,0)) "05",
sum(decode(to_char(first_time,'hh24'),'06',1,0)) "06",
sum(decode(to_char(first_time,'hh24'),'07',1,0)) "07",
sum(decode(to_char(first_time,'hh24'),'08',1,0)) "08",
sum(decode(to_char(first_time,'hh24'),'09',1,0)) "09",
sum(decode(to_char(first_time,'hh24'),'10',1,0)) "10",
sum(decode(to_char(first_time,'hh24'),'11',1,0)) "11",
sum(decode(to_char(first_time,'hh24'),'12',1,0)) "12",
sum(decode(to_char(first_time,'hh24'),'13',1,0)) "13",
sum(decode(to_char(first_time,'hh24'),'14',1,0)) "14",
sum(decode(to_char(first_time,'hh24'),'15',1,0)) "15",
sum(decode(to_char(first_time,'hh24'),'16',1,0)) "16",
sum(decode(to_char(first_time,'hh24'),'17',1,0)) "17",
sum(decode(to_char(first_time,'hh24'),'18',1,0)) "18",
sum(decode(to_char(first_time,'hh24'),'19',1,0)) "19",
sum(decode(to_char(first_time,'hh24'),'20',1,0)) "20",
sum(decode(to_char(first_time,'hh24'),'21',1,0)) "21",
sum(decode(to_char(first_time,'hh24'),'22',1,0)) "22",
sum(decode(to_char(first_time,'hh24'),'23',1,0)) "23",
count(to_char(first_time,'MM-DD')) Switches_per_day
from v$log_history
where trunc(first_time) between trunc(sysdate) - 6 and trunc(sysdate)
group by to_char(first_time,'DD-MON') 
order by to_char(first_time,'DD-MON') ;

Updated: The redo log files were sized at 25 MB. To relieve the database from this pain, I increased the size of the redo log files to 1 GB each.

Updated-2: Here is the post related to this.