Re: Impact of two databases sharing an oracle instance

In order to operate one database, you need at least one instance. However, in a RAC configuration, several instances can operate one database.

An instance can operate only one database at at time.

A database can, and should, have several schemas.

One schema, called SYS, is roughly equivalent to the 'Master Database' found in Sybase and it's spawn SQL Server. You should rarely, if ever, have to touch that directly. The remaining schemas are usually associated with applications.

If possible, try to achieve one instance per machine by combining multiple schemas into one database. There are several pros and cons to database consolidation, starting with the following:

Pros:

Fewer instances to manage;
Fewer instances and databases to upgrade; Fewer overall resources such as memory and CPU cycles;

           (you listed a few others)
Ability to use Oracle Resource Manager for load control.

Cons:

Sloppy security and use of 'PUBLIC' tends to cause issues; All apps must be upgraded at one time;

        (may impact testing time or have vendor issues) Recovery involves all apps.

         (see 10g's Flashback capability to get around this)

This is just the tip of the iceberg. I'm sure others will help expand this list.

-- 
Hans Forbrich                           
Canada-wide Oracle training and consulting
mailto: Fuzzy.GreyBeard_at_gmail.com   
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