Re: Sync redo log waits
Date: Tue, 19 Feb 2013 19:06:34 -0500
Message-ID: <CACqGOPJ_Z5VOc-MzT=9jmj2q9ihb9UNJ=HLve75RvESsGAH5ig_at_mail.gmail.com>
I just set ARCHIVE_LAG_TARGET to 15 min and this has what I got in last few hours:
DAY HOUR LOGSWITCH COUNT ---------- ---- ---------------------- 2013-02-19 16 17 2013-02-19 17 20 2013-02-19 18 22
On Tue, Feb 19, 2013 at 1:50 PM, Andrew Kerber <andrew.kerber_at_gmail.com>wrote:
> Oracle has a setting, archive_lag_target, that will force a log switch if
> one has not been done in the time frame specified by archive_lag_target.
> So when the redo activity is uneven, I usually set that parameter and set
> the redo logs to a very large size.
>
> On Tue, Feb 19, 2013 at 11:48 AM, Paul Houghton <
> Paul.Houghton_at_admin.cam.ac.uk> wrote:
>
>> Hi
>>
>> According to a number of oracle support notes, e.g. 147468.1 performance
>> will be impacted if log switches more often than about once every 15
>> minutes. That note specifically says that performance will be impacted by
>> switching once every 3 minutes, which is around what you are doing.
>>
>> So yes, you should increase the size of the redo logs to 4.5 - 6 times
>> their current size unless you are sure you can reduce the number of
>> switches by reducing the workload.
>>
>> We have a cron job which switches the log file every 15 minutes to ensure
>> the standby is up to date, though I am not sure if this is needed any more
>> (11.2).
>>
>> You may be able to talk with the application people to get them to spread
>> the load. Sometimes you get a trendy time to start a batch process (say
>> 2am) and everyone starts their process at this time, though I can't see a
>> pattern in the data you posted. Does the application keep some kind of log
>> or audit of what it was doing which you could consult to find out what was
>> being run, or use AWR reports if you have tuning pack, or even statspack
>> and tune that area of the application or move it to a quieter time?
>>
>> Hope this helps
>>
>> PaulH
>>
>>
>> --
>> http://www.freelists.org/webpage/oracle-l
>>
>>
>>
>
>
> --
> Andrew W. Kerber
>
> 'If at first you dont succeed, dont take up skydiving.'
-- http://www.freelists.org/webpage/oracle-lReceived on Wed Feb 20 2013 - 01:06:34 CET