All language subtitles for [SubtitleTools.com] The Oracle RDBMS - Instance And Database - Learning Oracle 12c [Video]

In this lesson, we want
to examine the difference

between the terms
instance and database

as they relate to the
Oracle Database System.

Oracle is a Relational Database
Management System, or RDBMS.

And what makes a RDBMS
is the fact that it

uses tables and relates the
data in the tables together

in order to form
things like joins

and to be able to separate
the data and yet still make

it relatable together,
whenever you need it.

And RDBMS is the most
common form of database

that's out there today.

There are many different
brands, if you will,

of RDBMS, such as MySQL, SQL
Server from Microsoft, and DB2.

And all of them have
some kind of difference

in their architecture.

The terms instance in
database mean different things

in different RDBMSs.

For instance, in
Microsoft SQL Server,

the term instance refers more
to the installation itself,

and the database refers
to a set of tables.

This is more like a
schema would be in Oracle

with that set of tables.

So it's important to understand
that different RDBMSs have

different uses of the terms.

For our purposes,
there are three reasons

to distinguish between an
instance and a database

in the Oracle RDBMS.

As we've said, in
other RDBMSs, the terms

mean different things.

Second of all, we can
see the relationship

between the instance
in the database

through their separation.

That is to say, having
a division of labor,

if you will, between an
instance in a database

helps us to more
clearly identify

what each component does.

And the third, and
probably most important,

is that the difference between
an instance and a database

is underscored by
two different Oracle

architectures-- single
instance database versus RAC.

In a single instance database
generally the instance

in the database are housed
together in a single system,

and that's by far the most
common type of Oracle database

that a DBA would find.

However, on RAC,
there's a separation,

a distinct separation between
an instance and a database.

Physical machines
involved are separated.

So let's define an instance.

An instance is composed of the
background processes and memory

structures in Oracle
necessary to do work.

So background
processes are going

to be individual processes that
are more aligned with the CPU

as far as a resource
in the computer.

We're going to see that each
one of these major components

in the instance
and database maps

to a resource in our computer.

So every computer has
three basic resources--

the CPU, the RAM and the disk.

And each one of these
major components

will map to those in
some direct fashion.

So background
processes are processes

that go out and do work,
they go out and do things,

and they align with the CPU.

The second component
of the instance

are the memory structures--
the caches, if you will.

And they map directly
to, of course, the RAM

in a system, the memory itself.

In Oracle, it's been said
that everything is a cache.

So in Oracle, the
background processes

tend to operate on data
within RAM or memory,

what we would call
an Oracle cache

rather than on the disk itself,
because RAM memory is orders

of magnitude faster than disk.

So those are the two
components of the instance.

The database as we define it is
composed of one main component,

and that are the data files.

So these are the actual
physical data files on the disk.

If they're in a file system,
you can go out to them

and see them.

If they're on Windows, you
can use your Windows Explorer

to go out and find them.

But they are files that
you actually see on disk,

and each one of
the data files has

a different job-- it stores
a different type of data.