|Subject:||Re: ReDo Log Advice from ixora web site|
|Posted by:||Niall Litchfield (n-litchfie…@audit-commission.gov.uk)|
|Date:||Fri, 23 Apr 2004|
"Charles" <cdavis107…@comcast.net> wrote in message
> the ixora web site give this advice about keeping ReDo log files open.
> Do the experts in this group generally concur with this advice?
> 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
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
Audit Commission UK
ReDo Log Advice from ixora web site posted by Charles on 22 Apr 2004