Steve, excuse me but I´m just curious about your answer : in my db, the
sync cost ratio is well under 1.5, but 'average log write size' is very
different of 'background write threshold'. What it means ?
[]s
J. Laurindo Chiappa
- cut here ----------------------------
Avgerage Log Background
Write Size Write Theshold
-------------- --------------
5632 87552
Sync Cost Ratio
0.95
In article <39cb197f.153804939_at_nsw.nnrp.telstra.net>,
steve.adams_at_ixora.com.au (Steve Adams) wrote:
> Hi Chuan,
>
> Have a look at the script "lgwr_stats.sql" at
> http://www.ixora.com.au/scripts/redo_log.htm. If the 'sync cost
ratio' reported
> by that script is approximately 1, then you can do nothing other than
attempt to
> reduce your commit frequency and optimize log file writes at the
operating
> system level.
>
> If the ratio is higher than 1.5, then you may have an instance tuning
problem
> worth investigating. If the 'log_buffer' is too small, it can
increase 'log file
> sync' times indirectly via 'redo allocation' latch contention. If so,
in
> addition to the latch contention itself in V$LATCH, the above script
would show
> that the 'average log write size' is of the same order of magnitude
as the
> 'background write threshold'. If not, then increasing
the 'log_buffer' size is
> not likely to have a significant impact, but if anything it would in
fact
> increase the average 'log file sync' time rather than reduce it. That
is
> explained in tip on the Ixora web site called "Tuning the Log Buffer
Size" at
> http://www.ixora.com.au/tips/tuning/log_buffer_size.htm.
>
> @ Regards,
> @ Steve Adams
> @ http://www.ixora.com.au/
> @ http://www.christianity.net.au/
> @
> @ Going to OpenWorld?
> @ Catch the Ixora performance tuning seminar too!
> @ See http://www.ixora.com.au/seminars/ for details.
>
> -----Original Message-----
> From: "Chuan Zhang" <chuan_at_asiaonline.net>
>
> At present, our production (Oracle EE 8.0.6, solaris 2.7) is using
156K for
> 'log_buffer'. The performance tunning for log buffer is ok. but
the 'log file
> sync' is bad. I cannot do anything to relocate the redo log files. I
think
> it might improve the performance to increase the log buffer or tuning
the
> log checkpoint interval.
>
>
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Received on Fri Sep 22 2000 - 07:04:47 CDT