Re: terminology - instance, user, tablespace

"Christoph Kukulies" <kuku_at_gil.physik.rwth-aachen.de> wrote in message news:9orv8g$ejh$1_at_nets3.rz.RWTH-Aachen.DE...
> I have a bit problems in understanding the term instance, users and
tablespace
> in Oracle or databases in general.
>
> An instance is identified by a SID, say ORC0.
> I assume, in unix terminology it is a server process that acts on a
> certain set of data.
>

Nope. An Instance is the SGA (ie, the Shared Pool, Log Buffer and Buffer Cache, plus Large Pool and Java Pool) together with the 5 compulsory background processes (PMON, SMON, LGWR, DBWR and CKPT), plus any of the optional background processes.

> When create table statements are executed by a certain user, these
> tables are unique in this instance, right? It is not possible
> to run two different sets of tables (tablespace?) for the same user in
> an instance.
>

Gawd... A tablespace is *not* a set of tables. It's an allocation of space to the database that will, for sure, contain a set of tables. Or indexes. Or rollback segments. Or clusters. Or temp segments. Or IOTs. Or Lob segments. Etc Etc.

But yes, a table called EMP created by SCOTT is unique. SCOTT can't create another table called EMP, though Mr. SYSTEM can quite happily do so.

> So when I want to have two different databases, say one with test data,
> the other with production data, I would have to create two instances.
>

Yes. Because a database cannot be accessed except through an Instance, and one Instance can only manage one database.

> Are the above considerations correct?
>

Sort of. Do yourself a favour, though, and really read around the subject. Tru www.geocities.com/howardjr2000/courses.htm and poke around. There are a couple of documents there that will get you started (try the Chapter 1 document under DBA).

Regards
HJR
>
> --
> Chris Christoph P. U. Kukulies kuku_at_gil.physik.rwth-aachen.de
Received on Fri Sep 28 2001 - 08:29:45 CDT