Re: Combining Data Guard with clustered redo logs for high performance standby

From: IANAL_VISTA <IANAL_Vista_at_hotmail.com>
Date: Wed, 17 Aug 2005 02:06:48 GMT
Message-ID: <Xns96B4C26E9AEADSunnySD@68.6.19.6>

Dennis G Allard <allard_at_oceanpark.com> wrote in news:430240AE.9050505_at_oceanpark.com:

> Mark Bole wrote:

>> Dennis G Allard wrote:
>> 
>>> Mark Bole wrote:
>>>
>>>> Dennis G Allard wrote:
>>>> [...]

>

>> I think I understand what you are trying to do -- recover the
>> physical standby with all available archived redo logs, then replace
>> the standby control file with the primary control file, copy the
>> primary online redo logs, and start up the database and let it
>> perform automatic instance recovery as if it were the primary.  I
>> doubt it will work, but there's no harm in testing.

>
> Actually, not 'copy' the redo logs. Instead, mount the physical
> partition containing the redo logs (etc.) on the Standby so that
> it now sees those files as its own. That is the essence of an
> active/passive cluster. What used to be files local to the Primary
> server become local files on the Standby after the Primary goes
> off line and the Standby mounts the partitions.
>

>> Step back and consider your two main goals: you want guaranteed zero 
>> loss of committed transactions, and you don't want any performance 
>> penalty for copying those transactions to a second location in real 
>> time.  I don't think it is possible in this case to get "something
>> for nothing".  Have you measured the actual impact of the performance
>> penalty?  Have you measured the actual impact of losing, say, ten 
>> minutes worth of transactions once every three years?

>
> In our case, I do agree that we can 'afford' to lose some transactions
> if it is very rare. But I also believe that the new clustering
> technologies (such as Red Hat Linux Cluster Suite) will make it
> possible to have ones cake and eat it too!
>
> I have scoured the web and USENET and Oracle docs. I am now convinced
> that this form of active/passive cluster database failover is not
> in common use. However, I see no reason that it cannot be
> implemented.
>

>> 
>> If you trust your external storage array, why not put your whole 
>> database on the external array, since you are already putting the 
>> control files, online, and archived redo logs there?  Do you know
>> that 

>
> As a matter of fact, I have decided to do just that! Because then I
> could use the active/passive failover technique by simply installing
> Oracle on a backup server but keep it turned off. Fail over would
> cause the backup server to mount the external disks and bring Oracle
> up (and, for that matter, take over the IP of the failed primary
> server).
>

>> having a physical standby requires another full Oracle license (false
>> claims to the contrary not withstanding)?  Do you know that Oracle 

>
> I just attended Linux Expo in San Francisco last week. Oracle reps
> stated that they have a 'ten day rule' -- as long as you don't use
> the standby server database more than ten days in the year, there is
> no license fee.
>

>> recommends never backing up online redo log files, which is very
>> similar to what you are trying to do?  Why not just set your archive
>> lag target 

>
> Again, I'm not copying redo logs. I'm merely remounting them to a
> different CPU box. I agree there is no point in backing up redo
> logs (as opposed to archived redo logs, which, of course, one should
> backup back to at least the last hot or cold backup of the database).
>

The mount point for redo logfiles mentioned immediately above could be a nasty single point of failure that could bring down both DBs. Received on Tue Aug 16 2005 - 21:06:48 CDT