Re: More than one RAC instance/database on the same machine ?

From: DA Morgan <damorgan_at_x.washington.edu>
Date: Sat, 30 Oct 2004 18:04:58 -0700
Message-ID: <1099184640.954877@yasure>

Howard J. Rogers wrote:

> DA Morgan wrote:
>
>

>>Le JeanMimi wrote:
>>
>>
>>>First, thank you for your answers.
>>>
>>>For us, the point is availability (and not scalability).
>>>
>>>Say we have two databases A and B and two machines.
>>>We put A and B in RAC configuration :
>>>- instance A1 and B1 on machine 1
>>>- instance A2 and B2 on machine 2
>>>(A1 and A2 for database A, B1 and B2 for database B)
>>>
>>>If the machine 1 crashes, then all the work being done by A1 and B1
>>>failover to machine 2 (TAF) and everything is very fast ... and
>>>transparent.
>>>
>>>Does it make sense ?
>>>Thanks (i'm rather new to this)

>
>
> [snip]
>
>

>>Makes no sense to me. Put one database on A, one on B and build two
>>schemas. 

>
>
> Precision! Do you mean "database" or "instance"?
>
> "One database on [node] A and one on [node] B" means there isn't necessarily
> a RAC any more.
>
>

>>Now you have half as many things to go wrong. What do you  
>>think you accomplish with 2 System tablespaces, 2 UNDO tablespaces, 2
>>SGAs? I mean accomplish as in desirable?

>
>
> Er, perhaps because you have two databases which behave quite differently,
> get backed up quite differently... why does any organisation ever need more
> than one database?
>
> The issue is not whether it's pure or not. Oracle's own tools quite happily
> let you add additional databases to an existing cluster, so they don't
> think the rule should always and forever be 'one cluster, one RAC
> database'. So it's do-able and it's acceptable.
>
> And if you've got a thumping great big hardware cluster, and one database
> isn't even getting close to stretching the thing; and you have a legitimate
> business or managerial reason for building a second database; why not put
> it on the slackly-used cluster, too?
>
> HJR
This is RAC ... one instance per server. Sorry for the lack of languge precision.

Can you explain to me how two databases behave quite differently? Databases don't behave on a node ... instances do. Thought I'd return the favour. ;-)

I've heard that argument before ... but you are speculating and from my experience I've yet to see a "real" situation where a second instance, rather than a second schema, was really required.

-- 
Daniel A. Morgan
University of Washington
damorgan_at_x.washington.edu
(replace 'x' with 'u' to respond)

Received on Sat Oct 30 2004 - 20:04:58 CDT