Re: Best Practice

From: <Laimutis.Nedzinskas_at_seb.lt>
Date: Thu, 19 Jan 2012 16:26:48 +0200
Message-ID: <OF64EC6264.EB3A78DF-ONC225798A.004E67AE-C225798A.004F5BD1_at_seb.lt>



>Marcin Przepiorowski <pioro1_at_gmail.com>
>It makes sens - if you use FSFO and primary database will loose
connection to standby database and to observer it will shutdown automatically preventing environment from split brain when primary DC will be available again.

ok, FSFO takes care of split brain. A standard "shoot yourself into your head" method is used.

>Is is possible to run observer in same place where are your end users
? It that case observer will see exactly same situation like your users.

Oracle is telling you "The observer should be installed and run on a computer system that is separate from the primary and standby systems "

The only question is from which point to observe both databases. IMHO, a natural answer: from your most important point. Take your most important functionality (e.g. authentication services) and make sure that observer detects when primary becomes unavailable to authentication purposes.

You need to draw the whole diagram: end user -> network -> load balancer -> network -> app servers -> database.

An interesting point is that observer MAY NEED to failover a primary database which is completely healthy just like in our case when network link between DS's was broken. And well, that is VERY correct - if standby is accessible then let the primary shoot itself down and use standby.

Brgds, Laimis N


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  From:       Marcin Przepiorowski <pioro1_at_gmail.com>                                                                                              
                                                                                                                                                   
  To:         Laimutis.Nedzinskas_at_seb.lt                                                                                                           
                                                                                                                                                   
  Cc:         ORACLE-L <oracle-l_at_freelists.org>                                                                                                    
                                                                                                                                                   
  Date:       2012.01.19 13:11                                                                                                                     
                                                                                                                                                   
  Subject:    Re: Best Practice                                                                                                                    
                                                                                                                                                   





On Thu, Jan 19, 2012 at 10:08 AM, <Laimutis.Nedzinskas_at_seb.lt> wrote:
> We had an interesting case: a network failure between our DC's (data
> centers - one is used as primary and the other as standby as far as
> databases are concerned)
>
>
> In our case observer runs on standby DC. It decided to failover of
course.
> The decision happened to be the correct one at least from admins point of
> view: the failover DC was still accessible to us, we could connect and
> restart what failed to failover, etc. End users could connect too.

It makes sens - if you use FSFO and primary database will loose connection to standby database and to observer it will shutdown automatically preventing environment from split brain when primary DC will be available again.

>
> You see: you need to consider what end customer functionality needs HA
most
> and start from that. What's the purpose to have a failover if the DC is
not
> accesible to the end users?
>
> If only isolated db/db server failure is concerned then you can run your
> observer on just a standby server. It will do the job: primary goes down,
> observer is running on standby, standby fails ower.
>

Is is possible to run observer in same place where are your end users ? It that case observer will see exactly same situation like your users.

regards,

--
Marcin Przepiorowski
http://oracleprof.blogspot.com
--
http://www.freelists.org/webpage/oracle-l





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Received on Thu Jan 19 2012 - 08:26:48 CST

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