Re: log file sync

terrysutton_at_usa.net wrote:

> I'm experiencing substantial waits on log file events, as seen below:
>
> Time Waited % Time
> Wait Event (min) Waited Waits (k) % Waits
> ----------------------------------- ----------- ------- --------- -------
> log file sync 538 55.94 1042 30.31
> db file sequential read 169 17.56 1170 34.05
> log file parallel write 123 12.82 989 28.79
> db file parallel write 95 9.90 35 1.03
>
>
> From this, it appears that log file sync wait time is about 4-5 times log
> file parallel write time. I've been looking at some of the advice on Steve
> Adams' IXOra site, and it seems that my "sync cost" is thus around 4, and I
> should probably have a smaller log buffer size. But when I run his
> lgwr_stats script, I get the following results:
>
> Average Log
> Write Size
> ---------------
> 2048
>
> Background
> Write Theshold
> ---------------
> 87552
>
> Sync Cost Ratio
> ---------------
> 1.13
>
> Which indicates a much lower sync cost. I realize this is not a "IXOra
> scripts forum", but which is the proper sync cost, and does my log buffer
> need to be smaller? It is currently 256K.
>
> --Terry
>
>
>

Hi Terry

Are you having a performance problem or are you 'just' tuning your ratio statistics? Have you heavy waits on redo allocation, redo copy, redo writing or the like? The (redo)log_buffer is written to disk when 1/3 full or 3 seconds have passed since last write or at a commit. And your statistics doesnt tell anything if they aren't comparable with how long the instance has been running. If it has been up 172 days, then a summed wait of about 56 seconds isn't a problem. Or?

/Svend Jensen Received on Mon Feb 25 2002 - 12:39:34 CST