Re: Two instances with same SID in a same machine

From: Howard J. Rogers <hjr_at_dizwell.com>
Date: Sat, 28 Aug 2004 13:00:15 +1000
Message-ID: <412ea3d7$0$27732$afc38c87@news.optusnet.com.au>

Mark Bole wrote:

>>

>
> Well, let's ask some questions. Could two different OS login users
> each have their own shared memory and semaphores? (assume some flavor of
> Unix, maybe under Windows too?) Check.
>
> Could two different OS users each have an ORACLE_HOME (base directory)
> at different places in the server filesystem, independent of each other?
> Check.
>
> Could one physical server have several TCP/IP addresses? Check.
>
> Could two listeners run on the same machine, each using port 1521 but a
> different TCP/IP address? Check.
>
> I don't have the means readily at hand to test this right now (oh, where
> have you heard that before? ;-) ), but I think it can be done.
>
> --Mark Bole

You can check all you want Mark. It's not going to happen.

Your questions can be simplified as:

On the one machine:

1. Can multiple distinct areas of shared memory be set up
2. Can you install Oracle multiple times
3. Can there be multiple IP addresses
4. Can there be multiple listeners.

No-one would have any qualms about agreeing with ANY of those.

My answers would be:

What do you think running two instances on a machine does?
People have been doing it for ages
Inevitably so... RAC wouldn't have much future otherwise
Obviously, though we would ordinarily question the point of doing it

That still doesn't address the actual question asked, however: can two areas of shared memory be referenced by exactly the same identifier (SID)? To which the answer is, try as you might, no.

As a VMware buff, of course, I would point out that it is utterly trivial to have identically-named instances on the one laptop, and I do it all the time. But each one of those instances has to be wrapped inside its own virtual machine... which is not quite what the OP had in mind, I suspect.

Regards
HJR Received on Fri Aug 27 2004 - 22:00:15 CDT