RE: High waits/Timeouts - log file parallel write

  • From: "John Kanagaraj" <john.kanagaraj@xxxxxxx>
  • To: <pele_00_2000@xxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
  • Date: Mon, 27 Feb 2006 17:31:06 -0800

Tom,

Are you having a lot of control file writes precipitated by a small redo
log file as compared to the redo size/rate and a large number of
datafiles? You should be able to check this from the number of datafiles
and redo log file/rate and have a feeling for amount of checkpoint I/O
by comparing V$SYSSTAT's 'physical writes non checkpoint' to 'physical
writes'. The former should lag the latter by a a very small
percentage....

Regards,
John Kanagaraj <><
DB Soft Inc
Phone: 408-970-7002 (W)
 
Co-Author: Oracle Database 10g Insider Solutions
http://www.amazon.com/exec/obidos/tg/detail/-/0672327910/
 
** The opinions and facts contained in this message are entirely mine
and do not reflect those of my employer or customers **


-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Steve Adams
Sent: Monday, February 27, 2006 4:56 PM
To: pele_00_2000@xxxxxxxxx
Cc: oracle-l@xxxxxxxxxxxxx
Subject: Re: High waits/Timeouts - log file parallel write

Hi Tom,

The 'log file parallel write' waits affect LGWR only. They do not affect
the performance of user processes directly (although they do impact
somewhat on your 'log file sync' wait duration). The number of timeouts
is influenced by your use of asynchronous I/O and by how often LGWR is
posted by user processes. It is not a useful indicator of performance
problems.

I think you should be more concerned about the 'control file parallel
write' waits that are probably affecting user processes directly.

@   Regards,
@   Steve Adams
@   http://www.ixora.com.au/         - For DBAs
@   http://www.christianity.net.au/  - For all


TP wrote:
> Hello all,
> 
> I seeing high Waits, Timeouts from one the problem instance.
> 
> Top 5 Timed Events
> ~~~~~~~~~~~~~~~~~~                               
>                      % Total
> Event                                            
>   Waits    Time (s) Ela Time
> --------------------------------------------
> ------------ ----------- --------
> CPU time                                         
>                   8    40.51
> control file parallel write                      
>     642           5    25.56
> db file sequential read                          
>     343           2     9.40
> log file parallel write                          
>   9,697           2     7.99
> log file sync                                    
>     425           1     5.69
>          
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