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RE: DB_WRITER_PROCESSES vs DBWR_IO_SLAVES

From: Thomas Jeff <jeff.thomas_at_thomson.net>
Date: Fri, 09 Jan 2004 14:34:44 -0800
Message-ID: <F001.005DC4C0.20040109143444@fatcity.com>


Jonathan,                                                   

                                          WILLING   IMMEDIATE
IMMEDIATE   IMMEDIATE               
NAME                   GETS    MISSES   TO WAIT %        GETS
MISSES   REQUEST %    SLEEPS     
=============== =========== ========= =========== ===========
=========== =========== =========     
redo copy             11448         0           0   599170378
405208 .0676281764         0     
redo allocation     6809468    247548 3.635350074   597056922
17812410 2.983368812     11018    

Thanks.

-----Original Message-----
Jonathan Lewis
Sent: Friday, January 09, 2004 3:35 PM
To: Multiple recipients of list ORACLE-L

One interpretation of increased red latch contention and log buffer space waits is that more work is being done more quickly - so the log writer can't keep up.

This could mean:

  1. the log writer has slowed down
  2. the database writer(s) have speeded up, so there is less time lost on write complete waits, free space waits, and (side effect) buffer busy waits.

So the symptoms could be positive or negative, and we don't have enough relevant information to say which. Depending on the nature of the application, and the number and duration of sync waits, you could address the log buffer space waits by increasing the size of the log buffer.

Are the redo latch waits allocation latch or copy latch ?

Regards

Jonathan Lewis
http://www.jlcomp.demon.co.uk

  The educated person is not the person   who can answer the questions, but the   person who can question the answers -- T. Schick Jr

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Now, the Sr DBA here is screaming about the performance since I made the change, in particular, he says he's seeing high redo latch contention and redo log buffer waits which he says validates his contention that we need to get back to
using DBWR_IO_SLAVES.

--

Please see the official ORACLE-L FAQ: http://www.orafaq.net
--

Author: Jonathan Lewis
  INET: jonathan_at_jlcomp.demon.co.uk

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Author: Thomas Jeff
  INET: jeff.thomas_at_thomson.net
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