RE: Real-time Apply in DataGuard

  • From: D'Hooge Freek <Freek.DHooge@xxxxxxxxx>
  • To: "Brandon.Allen@xxxxxxxxxxx" <Brandon.Allen@xxxxxxxxxxx>, Andrew Kerber <andrew.kerber@xxxxxxxxx>, "oracle-l@xxxxxxxxxxxxx" <oracle-l@xxxxxxxxxxxxx>
  • Date: Tue, 21 Sep 2010 21:16:08 +0200

Allen,

With lgwr async you still have the possibility to impact your primary datatase 
(although you need to have a really bad situation, before it will emerge):

With lgwr async your lns process is reading from the online redo logfile and 
sends the redo vectors to the standby database.
If all is fine, the lns process is just behind the poin the point where the 
lgwr is writing.
However, if your network latency to the standby db is to high for the amount of 
redo you are generating, the lns process can fall behind.
In the case that the lns process is so far behind that it is still reading from 
logfile n, while the lgwr is already writing to logfile n+2, then an 
optimization kicks in and the lns process will skip the logfile n+1 (it will be 
transferred via the arch process).
However, if the lns process is even further behind and the lgwr wants to start 
writing to the logfile from which the lns process is still reading, then the 
database will halt until the lns process has finished reading that logfile.

Regards,

Freek D'Hooge
Uptime
Oracle Database Administrator
email: freek.dhooge@xxxxxxxxx
tel +32(0)3 451 23 82
http://www.uptime.be
disclaimer: www.uptime.be/disclaimer
--
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On 
Behalf Of Allen, Brandon
Sent: dinsdag 21 september 2010 19:42
To: Andrew Kerber; oracle-l@xxxxxxxxxxxxx
Subject: Real-time Apply in DataGuard

I'm starting a new thread specific to real-time apply.  

That is my fear - that by using real-time apply we might impact the performance 
or availability of the production database if there are network problems 
between the primary and standby.  We had problems with that the last time I 
tried to implement Data Guard in 9.2.0.4, but according to the documentation it 
sounds like that shouldn't happen anymore in 10.2.  For example, from page 22 
of the doc linked below: "In Oracle Database 10g Release 2, the new LGWR ASYNC 
behavior eliminates the potential to stall the production database"

http://www.oracle.com/technetwork/database/features/availability/maa-wp-10gr2-dataguardnetworkbestpr-134557.pdf

Has anyone done any testing to confirm if network problems can impact 
performance of the primary when using real-time apply in 10.2 (10.2.0.4.3 
specifically in my case)?  I'll be testing it myself soon, but am still curious 
to know what others have found.


Thanks,
Brandon

From: Andrew Kerber [mailto:andrew.kerber@xxxxxxxxx] 
I have never implemented real-time apply, but it is my understanding that there 
are performance issues when there are problems with the network 

On Tue, Sep 21, 2010 at 11:16 AM, Allen, Brandon <Brandon.Allen@xxxxxxxxxxx> 
wrote:
Why not use real-time apply instead?  


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