Oracle – DBA Basics

Varinder Sandhu Oracle, Oracle-Tips and Tricks, Varinder Sandhu

First I would like to share some background of this post. As I have SQL Server background (you can see in my profile here) and when I started learning Oracle. I have so many basic questions regarding oracle environment. Even I was little lit bit confused about few things. But when I got the answer of my question then I thought I should write here on my blog.

Oracle and SQL server are very different products. There is no comparison between Oracle and SQL Server.

Some Oracle DBA Basics …

One machine can have multiple oracle instances.
Only a single database is associated with an oracle instance.
One database can have multiple schemas with the different names.

Instance

Every running Oracle database is associated with an Oracle instance. When a database is started on a database server (regardless of the type of computer), Oracle allocates a memory area called the System Global Area (SGA) and starts one or more Oracle processes. This combination of the SGA and the Oracle processes is called an Oracle instance.

Schema

A schema is the set of objects (tables, views, indexes, etc) that belongs to an user account. It is often used as another way to refer to an Oracle account.

Database

An Oracle database consists of one or more logical storage units called tablespaces, which collectively store all of the database’s data.

Tablespace

Each tablespace in an Oracle database consists of one or more files called data files.

Data files

A database’s data is collectively stored in the data files that constitute each tablespace of the database.