Re: LOG_BUFFER

From: Ram Raman <veeeraman_at_gmail.com>
Date: Wed, 1 Jun 2016 23:11:28 -0500
Message-ID: <CAHSa0M3xF_1yi6QQ0CkiQzMJ4UXvEu3R6jMiUNVhxPEyaFLbTA_at_mail.gmail.com>

Curious, what backup strategy do you use to backup a 500Tb database. Does the full backup complete in 1 day.

How long do the incrementals take? With that many changes, CTWR (block chg trking) process will be in full swing pretty much all the time?

On Fri, May 20, 2016 at 7:32 AM, Ram Cheruvattath < ram.cheruvattath_at_gmail.com> wrote:

> Thanks Robert! I will check the notes you mentioned.
>
> Ram
>
> *From:* Robert Freeman <rfreeman_at_businessolver.com>
> *Sent:* Thursday, May 19, 2016 2:49 PM
> *To:* gogala.mladen_at_gmail.com ; oracle-l_at_freelists.org
> *Subject:* RE: LOG_BUFFER
>
> One interesting support document has to do with a bug related to adaptive
> log file sync being enabled in 11.2.0.3. See document 1462942.1 hangs
> related to adaptive log file sync – describes bug 13930580.
>
> Also document 1541136.1 provides a bit more information about the adaptive
> log file sync method, which also highlights a couple of additional bugs
> related to this new 11gR2 feature.
>
>
>
>
>
> *From:* oracle-l-bounce_at_freelists.org [mailto:
> oracle-l-bounce_at_freelists.org] *On Behalf Of *Mladen Gogala
> *Sent:* Wednesday, May 18, 2016 8:35 PM
> *To:* oracle-l_at_freelists.org
> *Subject:* Re: LOG_BUFFER
>
>
>
> On 05/17/2016 02:59 PM, Ram Cheruvattath wrote:
>
> Hi
>
>
>
> We have a 12c database that has very high redo generation (4TB/hr). Our
> log_buffer is set to 1GB.
>
>
>
> Is there a downside to setting log_bugger this big?
>
>
>
> Thanks
>
> Ram
>
> Ram, we have talked about multi-threaded log writer in 12c few days ago.
> In the meantime, I did some digging and found some new undocumented
> parameters:
>
> _adaptive_scalable_log_writer_enable_worker_threshold Increase in redo generation rate as a percentage
>
> _adaptive_scalable_log_writer_disable_worker_threshold Percentage of overlap across multiple outstanding writes
>
> _adaptive_scalable_log_writer_sampling_count Evaluate single versus scalable LGWR every N writes
>
> _adaptive_scalable_log_writer_sampling_time Evaluate single versus scalable LGWR every N seconds
>
> _adaptive_scalable_log_writer_enable_worker_aging Per million of redo gen rate when LGWR workers were last used
>
>
>
> Of course, there is nothing about these parameters on the
> support.oracle.com. The good, old times when it was possible to figure
> out how things work by digging through the Oracle support documents are a
> long gone era. However, I was able to dig out few things from Jonathan's
> site:
>
> https://jonathanlewis.wordpress.com/2013/07/04/12c-trivia/
> https://jonathanlewis.wordpress.com/2013/06/25/12c/
>
> Not much more than we've already discussed, but still worth reading. I
> would expect multi-threaded writer to be able to cope with much larger
> buffers than we have seen in 11G. I don't think that in 12c having 1G log
> buffer is a bad idea. However, the only sign you will get that your log
> buffer is too small are log buffer space wait events in V$SYSTEM_EVENT. I
> guess that there is a feature called "adaptive scalable log writer" which
> will appear in some kind of an internals book when people at Oracle Corp.
> decide do tell someone about it.
>
> --
>
> Mladen Gogala
>
> Oracle DBA
>
> Tel: (347) 321-1217
>
>

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Received on Thu Jun 02 2016 - 06:11:28 CEST