Re: log_buffer sizing

From: Stefan P Knecht <knecht.stefan_at_gmail.com>
Date: Tue, 16 Aug 2011 07:20:40 +0200
Message-Id: <266D6B63-B37E-41CD-BF48-26189BDBC8E0_at_gmail.com>

And in addition to Tim's reply - how many redo log groups are there?

Adding more groups can give the archivers an additonal buffer to do their job during peaks.

Stefan

On 16.08.2011, at 01:13, K R <kp0773_at_gmail.com> wrote:

> Tim,
>
> once in a while we see wait on the toad ( log file waiting to be archived ) and as the log buffer is only 20MB and the online logs are 3GB so we were discussing if we can do as per any recommended sizing .
>
> Thanks
> Kart
>
> On Mon, Aug 15, 2011 at 1:12 PM, Tim Gorman <tim_at_evdbt.com> wrote:
> Kart,
>
> There is no magic bullet in that query, it was just for your information, so you can provide something more useful than the size of your online redo log files.
>
> So, asking again: what are you seeing that made you say, "the log buffer seems too small". From this query, you can see when redo generation gets high. During those times, are you seeing anything that indicates any kind of "bottleneck" in redo processing?
>
> Thanks!
>
> -Tim
>
> -----Original Message-----
> From: K R [mailto:kp0773_at_gmail.com]
> Sent: Monday, August 15, 2011 02:01 PM
> To: tim_at_evdbt.com
> Cc: Oracle-L_at_freelists.org
> Subject: Re: log_buffer sizing
>
> Tim,
> this is a typical workload when the batch is running on the database.
>
> DAY HR NBR_SWITCHES GB
> ----------- ----- ------------ -----------
> 13-AUG-2011 00:00 12 3.84
> 01:00 12 8.46
> 02:00 30 51.52
> 03:00 38 60.86
> 04:00 36 61.56
> 05:00 43 72.49
> 06:00 43 55.48
> 07:00 12 0.45
> 08:00 12 0.03
> 09:00 12 0.26
> 10:00 12 6.42
> 11:00 12 3.89
> 12:00 12 0.25
> 13:00 12 2.35
> 14:00 12 0.04
> 15:00 13 1.90
> 16:00 41 72.73
> 17:00 32 55.27
> 18:00 37 44.95
> 19:00 12 0.10
> 20:00 12 0.05
> 21:00 12 0.05
> 22:00 12 3.65
> 23:00 14 16.64
> *********** ***** -----------
> sum 523.25
>
>
>
> On Mon, Aug 15, 2011 at 12:52 PM, Tim Gorman <tim_at_evdbt.com> wrote:
> Kart,
>
> What exactly are you seeing in the database that makes you say "it just seems too low"?
>
> Bear in mind that the size of the online redo log files has no causal relation to the size of the log buffer, and vice-versa. What matters is the rate with which redo is written, and the frequency of COMMIT commands by the application.
>
> For the first bit of information, try the following SQL*Plus script...
>
> clear breaks
> break on day skip 1 on hr on report
> compute sum of gb on day
> compute sum of gb on report
> col sort0 noprint
> col cnt format 999,990
> col gb format 999,990.00
> select trunc(completion_time,'HH24') sort0,
> to_char(trunc(completion_time,'HH24'),'DD-MON-YYYY') day,
> to_char(trunc(completion_time,'HH24'),'HH24')||':00' hr,
> inst_id,
> count(*) nbr_switches,
> sum(blocks*block_size)/(1048576*1024) gb
> from gv$archived_log
> group by trunc(completion_time,'HH24'),
> to_char(trunc(completion_time,'HH24'),'DD-MON-YYYY'),
> to_char(trunc(completion_time,'HH24'),'HH24')||':00',
> inst_id
> order by 1, 2, 3, 4;
>
> That will give you some idea of the rate and volume. Of course, this query may end up double-counting redo volumes if you have additional archive destinations set up, so be aware of that and adjust accordingly.
>
> Hope this helps...
>
> Thanks!
>
> -Tim
>
>
> -----Original Message-----
> From: K R [mailto:kp0773_at_gmail.com]
> Sent: Monday, August 15, 2011 01:22 PM
> To: Oracle-L_at_freelists.org
> Subject: log_buffer sizing
>
> All ,
>
> my online redo logs are 3G . This is a batch intensive datawarehouse application. What should i be keeping my log_buffer .
>
> currently it is set at 29425664 and it just seems too low .
>
> thanks
> Kart
>
>

--
http://www.freelists.org/webpage/oracle-l

Received on Tue Aug 16 2011 - 00:20:40 CDT