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Re: ReDo Log Advice from ixora web site

From: Joel Garry <joel-garry_at_home.com>
Date: 22 Apr 2004 15:35:56 -0700
Message-ID: <91884734.0404221435.5f462626@posting.google.com>


cdavis10717_at_comcast.net (Charles) 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.

Far be it for me to disagree with anything he says, but I wouldn't call it the greatest potential. I took off minutes by getting rid of a stupid remote destination and replacing it with a cron. At least out-of-context-as-quoted, he seems to be underestimating the impact of such actions as checkpointing, not to mention things being severely mistuned or hardware contention issues ( http://www.ixora.com.au/tips/tuning_log_switches.htm for some context).

Six seconds is a surprisingly long time for 2002 vintage hardware. It's kind of odd Oracle closing the previous usage of the file would cause unix to forget where it is so completely, if that is what is happening. I suspect this would be very configuration-dependent. All unix has to do is lookup the inode in the directory that it already must know about from the other open log files there, if that is taking 6 seconds, man, something must be wrong, even if it does have to write directory information updates at those times. Maybe he's got 64 Oracle mirrors on RAID-5 or something, or maybe it only applies to raw...

jg

--
@home.com is bogus.
http://trekweb.com/articles/2004/04/22/4087eed3394be.shtml
Received on Thu Apr 22 2004 - 17:35:56 CDT

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