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Re: log writer tuning

From: Syed Jaffar Hussain <sjaffarhussain_at_gmail.com>
Date: Wed, 21 Feb 2007 17:33:40 +0300
Message-ID: <97b7fd2f0702210633w53590274j39c24693f799e7e4@mail.gmail.com>


Remigiusz,

What are the common log wait events which are encountering at the db level? Is it log file synce or log file sequential write or etc.

Having log_buffer size some time causes 'log file synce'.

Jaffar

On 2/21/07, Remigiusz Sokołowski <rems_at_wp-sa.pl> wrote:
>
> Hi!
>
> Problem:
> in monitoring (OEM) we have got "needles" on activity figure (RDBMS ver.
> 10.2.0.1).
> We believe slow log writer is responsible for them.
>
> Question:
> what can we do about it?
>
> Considerations:
> 1. we have quite high commit rate and maybe this is our main problem,
> then solution would be some new fast storage for redo logs - but this
> solution is the last one to consider due to costs
>
> 2. log_buffer is very big (64M, so 1:1 to redo log files size) - we
> could set it to lower value
> may be that is why we have got those "needles" on diagram.
> But in docs for 10gR2 they say:
> "sizing the log buffer larger than 1M does not provide any performance
> benefit. Increasing the log buffer size does not have any negative
> implications on performance or recoverability."
> Is it really no negative implications ?
> At http://www.ixora.com.au/tips/tuning/log_buffer_size.htm there is
> different opinion:
> " However, if the log buffer is very big, then the default
> /_log_io_size/ threshold will be big also, and so background writes may
> seldom be triggered. This means that all the redo will have to be
> flushed by sync writes, and so /log file sync/ waits will take longer
> than otherwise. This impacts commit response time, and possibly DBWn
> performance as well."
>
> 3. our redo logs are placed on the same mount point as datafiles - we
> could move them to some other mount point
> Does it change anything, if we move to separate mount point?
> Storage system is a JBOD in architecture RAID10 (so actually as
> indicated in SAME concept) composed as one large space. File system is
> UFS with set flag forcedirectio - according to our sysadmin writes of
> log writer doesn't block other processes on mount point.
>
> 4. Are there other parameters for log writing?
>
> Thanks for any comments
> Remigiusz
>
>
>
>
> --
> ---------------------------------------
> Remigiusz Sokolowski <rems_at_wp-sa.pl>
> WP/PTI/DIP/ZAB (+04858) 52 15 770
> MySQL v. 4.x
> Oracle v. 10.x
> ---------------------------------------
>
> --
> http://www.freelists.org/webpage/oracle-l
>
>
>

-- 
Best Regards,
Syed Jaffar Hussain
Oracle ACE
8i,9i & 10g OCP DBA

http://jaffardba.blogspot.com/
http://www.oracle.com/technology/community/oracle_ace/ace1.html#hussain
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Received on Wed Feb 21 2007 - 08:33:40 CST

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