Re: Multiple instance with multiple version of Oracle

"Useko Netsumi" <usenets_at_nyc.rr.com> wrote in message news:b2e7ff$1b3pp2$1_at_ID-159205.news.dfncis.de...
> Thanks again Howard. It's been a good learning information you gave me.
>
> At present I am able to run Oracle 9i with 192MB memory and 400MB swap
> space. I will try what you suggested by installing the 2nd instance for
the
> Oracle 8i.
>
> Thank you very much for your help.
>
> /useko
>
>
> "Howard J. Rogers" <howardjr2000_at_yahoo.com.au> wrote in message
> news:pan.2003.02.12.19.05.38.245973_at_yahoo.com.au...
> > On Wed, 12 Feb 2003 13:53:16 +0000, Useko Netsumi wrote:
> >
> > > Thank you Howards, it seems that I have to use the1st option(have 2
> > > instances running)
> > >
> > > Just to explain my reason, that I have a very limited
> resources(diskspace,
> > > memory, and an AMD box) . Diskspace I can add an external SCSI but I
> have
> > > limited memory.
> > >
> > > It would be nice if I can find a workaround to create both 9i and 8i
> > > database in the same box using one(1) instance only - so it does not
> take
> > > up more memory. I guess what I'm asking is that can oracle share SGA
> with
> > > different version of Oracle? Does it make any sense?
> > >
> > > Thanks again in advance.
> > >
> > > PS: Please forgive my lack of knowledge...
> > >
> >
> > Nothing to forgive: we all had to start somewhere.
> >
> > Now I see what you are after, I'm afraid the answer is a definite no. An
> > Oracle SGA (as you put it... an 'Instance' = SGA+other things) can only
> > ever manage one database. You want the one SGA to manage two databases
> > simultaneously... that can never happen, not even in a cluster.
> >
> > But be aware that whilst a database is permanent (stored on disk), the
> > instance is purely temporary: you can shut it down or start it up at
will.
> > If this is a home computer and you want only to learn about Oracle, then
> > there's nothing to say you have to have both instances running at the
same
> > time. Want to do some 8i work? Startup the 8i instance, and open the 8i
> > database with it. Time to switch to 9i? Shutdown the 8i instance, change
> > your ORACLE_SID, startup the 9i instance, open the 9i database.
> >
> > Also bear in mind that an instance can be really quite small: I've got
two
> > running at the moment that are only 50MB or so each. You'll have to tune
> > them that way, since the Oracle GUI tools you might use to create the
> > databases seem to assume everyone has at least 500GB of RAM going spare!
> > (I exaggerate slightly!!).
> >
> > Finally, although the minimum recommended RAM for 9i is 512MB, you can
> install it
> > with just 192MB (you might be able to take it even lower, but it failed
> > when I tried 128MB). So if you are going to install 9i at all, I'd
assume
> > you have at least 192MB of RAM -and, with the installs safely out of the
> > way, that should be sufficient to run two very small instances
> > simultaneously purely for learning purposes (they'll be very slow, but
> > they'll work).
> >
> >
> >
> >
>
>

Useko,

Everything Howard is saying is correct, but just in case it helps to clarify the terminology: No-one installs an instance.

What follows is a simplistic explanation, but it may help:

An Oracle installation is a version of the Oracle software installed on a machine. You can have multiple Oracle installations on one machine, and they can, if you wish (and FWIW we do it this way) all be owned by the same OS user.

A database is a set of physical data files. You can have multiple databases on the same machine, but each database is at a specific version. There is no problem with having several databases simultaneously at the same version.

An instance is a set of running background processes, combined with a set of memory structures (i.e. the System Global Area, plus the SMON. PMON, DBWR etc). So you can stop and start instances, but to create or delete databases means creating a set of files on the disks, or deleting them.

An instance can only open one database. However, multiple instances (on different macines, using a shared-disk setup) can open the same database concurrently; that is parallel server, or RAC. Each instance manages its own memory structure, but the instances have to co-operate to share the database files (and in fact there is co-operation between the memory structures too, for performance reasons).

HTH. Regards,
Paul Received on Thu Feb 13 2003 - 12:39:53 CST