Re: Multiple databases managed by one instance

A copy of this was sent to Wes Gamble <weyus_at_worldnet.att.net> (if that email address didn't require changing) On Thu, 28 Oct 1999 09:14:22 -0500, you wrote:

>Hi there.
>
>Being an Informix person, it's taken me a while to get used to the
>common idea that one instance = one database under normal Oracle usage.
>But I would like to buck this trend. I'd like to have one instance
>manage more than one database. How do I go about doing that? It
>appears that the init.ora files are database - specific - do I simply
>specify the same instance name in two different init.ora files?
>
>Anyone have any advice on what's a reasonable number of databases to
>allow to be managed by one instance?
>

one.

>Thanks,
>Wes Gamble

A database in Oracle is a collection of files (datafiles, control files, redo files).

An instance in Oracle is a chunck of shared memory and some processes (dbwr, lgwr, etc).

A database may be mounted by >1 instance (this is called Oracle Parallel Server).

An instance mounts 1 and exactly 1 database at a time.

In Informix, you have a "logical" concept of a database inside the database. This gives you the ability to 'pick' a database and then have a bunch of owner.tablenames available. If i 'pick' another database in the same database -- i have a different set of owner.tablenames available. It in effect gives me 3 nodes in my object names -- database.owner.table.

Oracle does not have this third node and it is nothing more then a naming convention. We have owner.table. Typically in Informix apps -- people never used the owner in the owner.table (unless they were in a mode ansi database but most people did not use that). They would pick a database and then "select * from emp".

You could/should use a SCHEMA (owner) in Oracle much like you used a 'database' inside the database in Informix.

--
See http://osi.oracle.com/~tkyte/ for my columns 'Digging-in to Oracle8i'... Current article is "Part I of V, Autonomous Transactions" updated June 21'st  

Thomas Kyte                   tkyte_at_us.oracle.com
Oracle Service Industries     Reston, VA   USA

Opinions are mine and do not necessarily reflect those of Oracle Corporation Received on Thu Oct 28 1999 - 09:23:13 CDT