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Re: redo log stats

From: Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk>
Date: Wed, 10 Jan 2001 07:13:34 -0000
Message-ID: <979110606.27978.0.nnrp-14.9e984b29@news.demon.co.uk>

Comments in line:

--
Jonathan Lewis
Yet another Oracle-related web site:  http://www.jlcomp.demon.co.uk

Practical Oracle 8i:  Building Efficient Databases

Publishers:  Addison-Wesley
See a first review at:
http://www.ixora.com.au/resources/index.htm#practical_8i
More reviews at: http://www.jlcomp.demon.co.uk/book_rev.html



Taki P wrote in message ...

>"Jonathan Lewis" <jonathan_at_jlcomp.demon.co.uk> wrote in message
>news:979085327.15378.0.nnrp-12.9e984b29_at_news.demon.co.uk...
>>
>> Taki P wrote in message ...

>> A worst case could be very high - this typically
>> would be caused by having log_buffer too small.
>
>I assume user processes don't cause more than one event per process
>per switch, then worst case must be about 'switches x typical number
>of concurrent transactions'. Maybe I'm missing something obvious here.
>
When the log buffer is too smal, you start to get log buffer waits which are not due to log switches - remember I said 'one of the reasons for .... is log switches' When the buffer is small, it can get filled very rapidly and then everything waits whilst it is written out, then restarts.
>>
>> Having a too big redo buffer is more likely to lead to high
>> values in v$session_wait for 'log sync' and 'log write'.

>
>I was under the impression that log sync waiting is posted by
>COMMITing transactions only.
>
Correct - but if the buffer is big, and lots of items go into it before a single commit occurs, then a lot has to be written out before the sync is complete. In this case I meant 'large amounts of time' rather than 'large counts' when I used the expression 'high values'.
Received on Wed Jan 10 2001 - 01:13:34 CST

Original text of this message

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