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Describe Oracle architecture in brief. 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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