Re: Sync redo log waits
- From: Andrew Kerber <andrew.kerber@xxxxxxxxx>
- To: Paul.Houghton@xxxxxxxxxxxxxxx
- Date: Tue, 19 Feb 2013 12:50:10 -0600
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@xxxxxxxxxxxxxxx> 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
>
>
> --
> //www.freelists.org/webpage/oracle-l
>
>
>
--
Andrew W. Kerber
'If at first you dont succeed, dont take up skydiving.'
--
//www.freelists.org/webpage/oracle-l
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