Describe Oracle architecture in brief.

Describe Oracle architecture in brief.

Answer
The Oracle database has:

- Logical layer: The components of the logical layer map the data to these physical components

- Physical layer: The physical layer consists of the files that reside on the disk

Tablespaces and Datafiles

The database is divided into one or more logical pieces known as tablespaces. A tablespace is used to logically group data together

The Database Schema: A collection of logical-structure objects, known as schema objects.

These schema objects consist of structures such as:
- tables,
- clusters,
- indexes,
- views,
- stored procedures,
- database triggers, and
- sequences.

Segments, Extents, and Data Blocks
Within Oracle, the space used to store data is controlled by the use of logical structures. These structures consist of the following:

* Data blocks--A block is the smallest unit of storage in an Oracle database. (contains header information concerning the block itself as well as the data)

* Extents--Extents consist of data blocks.

* Segments--A segment is a set of extents used to store a particular type of data.

The Oracle Instance has:

* User processes
* Oracle background processes
* The shared memory

The Oracle Memory Structure contains:

* The System Global Area (SGA)
* The Data-Dictionary Cache
* The Program Global Area (PGA)

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