Re: new instance / database

"Ben Heuer" <queerczarNOquSPAM_at_unforgettable.com.invalid> wrote in message news:0bb77d92.3b0e49b7_at_usw-ex0102-084.remarq.com...
> 1. Can you explain the same thing on NT? When I created my
> server, I created MYORCL as the SID..is this the database? Or is
> this the instance?
>

Put it this way: an Instance exists only in memory. It's a whole heap of virtual, memory structures whose sole job is to manage a database. When you edit a Word document, you don't do it by directly writing to file.doc on your c: drive -you load the thing into memory first, do all the edits in memory and (if the thing doesn't crash first!) eventually you do a file-save, and write the contents of memory back down onto disk. That's (sort of) what the Instance does. It's where all the workings of Oracle actually takes place. It contains processes which (sort of) do file-saves for you, automatically.

The Database *only* consists of the physical disk files. An Oracle database consists of control files, data files and redo logs. They all reside on disk, chew up space, and are read from and written to by the memory processes (ie, components of the Instance).

What this boils down to is that you *never* connect to a database. You are always connecting to an Instance which happens to be managing a database.

When you set ORACLE_SID=MYORCL, all you are doing is setting an environment variable. It happens to be an environment variable, however, which Oracle uses to name the Instance that is about to be created, or the Instance to which you wish to conect by default (unless you explicity state otherwise with a tnsnames alias). You have to name your Instances, because there could be dozens of them running on the same box -we've got to have some mechanism for keeping track of which one is which.

If, however, you want a one-line answer to you question, I'd say that setting a SID means you are working with your Instance. When you start talking file names, then you know you're working with your database.

Hope that helps a bit,
HJR
> 2. I checked the Technet, but there is nothing like a concepts
> manual. I'd really appreciate if you could send me a link!
>
>
>
>
> -----------------------------------------------------------
>
> Got questions? Get answers over the phone at Keen.com.
> Up to 100 minutes free!
> http://www.keen.com
>
Received on Sat Jul 29 2000 - 00:00:00 CDT