Re: Creation of Oracle databases

Not quite sure what the MySql definitions of Instance and Database are - probably subtly different from Oracle's definitions.

Quick rundown of Oracle's side (not comprehensive - I'm trying to be brief):

Instance - the set of processes & memory used to connect to a 'database' Database - one set of SYS & SYSTEM schemas, plus the set of schemas that you create
Userid - generally associated with a user, has a password, has specific authorizations & permissions within the instance Schema - collection of (related) objects (tables, columns, functions, triggers, etc.) owned by one (or more) userids. Other systems may refer to this as a database. Ther is no practical limit to the number of schemas in a database.
Grants - set of authorizations & permissions given to a userid to operate
within an instance as well as the ACL equivalent to access objects within
one or more schemas.

Tablespace - a logical construct for storage. If you think of Oracle as an operating system, then tablespace is equivalent to disk. A tablespace
maps to one or more physical disk files to provide storage for any number
of objects.

SYS - the schema owner for the master dictionary (referred to as a Master
Database by some other systems)
SYSTEM - the primary userid initially created for DBA activities.

>From this, and reading between the lines, I suspect the MySQL 'databases'
are roughly equivalent to Oracle 'Schemas'.

Since terminology and subtle differences betwen RDBMSs can be extremely frustratng, I recommend the O'Reilly "Oracle Essentials" book found at http://www.oreilly.com/catalog/oressentials/ or http://www.oreilly.com/catalog/oressentials2/ to get you up to speed before tackling the manuals.

HTH
/Hans

Meng wrote:

> Hi,
> We will migrate Mysql to Oracle soon. Now I have a question. We have
> 5 databases in one instance in Mysql. Do we need to create 5 databases
> in Oracle, or only one? We have to start 5 instances and assign
> different sizes of RAM to them If we create 5 databases. Thanks in
> advance.
>
> Meng
Received on Sat Jul 21 2001 - 23:15:53 CEST