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Re: ReDo Log Advice from ixora web site

From: Niall Litchfield <n-litchfield_at_audit-commission.gov.uk>
Date: Fri, 23 Apr 2004 08:58:44 +0100
Message-ID: <4088ccb5$0$26193$ed9e5944@reading.news.pipex.net>


"Charles" <cdavis10717_at_comcast.net> wrote in message news:83dbb3cd.0404221022.3f6153fa_at_posting.google.com...
> the ixora web site give this advice about keeping ReDo log files open.
>
> Do the experts in this group generally concur with this advice?
>
> Charles
>
> Copy/Paste from ixora web site:
>
> Holding the log files open
> The greatest potential for tuning the speed of a log switch is in the
> opening of the new log file members. The operating system's open()
> system call is much faster if another process already has an open file
> descriptor on the same file. This is partly because certain
> information about the file is already cached in kernel memory. But
> more importantly in the case of raw logical volumes, it avoids a delay
> while logical volume state data reflecting the opening of the raw
> logical volume is written to the volume group reserved area on disk.
>
> The APT script hold_logs_open.sh is intended to be run daily from cron
> under Unix to hold all the log files for an instance open for the next
> 24 hours. The first time we tried this technique, it shaved an
> impressive 6 seconds of the speed of each log switch. Your mileage
> will vary depending on your logical volume or file system and kernel
> configuration, but it is sure to help a little.

Like Joel I'm hesitant to disagree with Steve but I would note a couple of things.

  1. The script and associated question were written in the 7.3/8.0 timeframe. Perfomance of checkpointing and log switches has improved since then.
  2. How often do you log switch? The 'conventional wisdom' seems to suggest that about every 15 minutes would be a 'good' frequency. Is saving 6 seconds every 15 minutes going to make a significant difference?
  3. Do a sanity check on the 6 second figure. Do you actually get that improvement.
-- 
Niall Litchfield
Oracle DBA
Audit Commission UK
http://www.niall.litchfield.dial.pipex.com/
Received on Fri Apr 23 2004 - 02:58:44 CDT

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