Oracle Storage structure

What is storage structure?

While storing data, it get’s store logically in tablespace and physically in datafiles.

Storage structure:-

Logical storage structure:-

1)    Tablespace:-

A tablespace is a logical storage unit within an Oracle database. The tablespace is made up of one or more datafiles which are stored in the server's file system. A datafile belongs to one and only one tablespace but one tablespace can belongs to one or many datafiles.

2)    Tables:-

Tables are the basic unit of storage. Again it stores data logically in the format rows and columns.

3)    Rows:-

Rows are combination of all the fields is called rows.

4)    Column:-

Column is a list of values in fields.

Physical storage structure:-

1)    Datafiles:-

Database datafiles are physical files stored on disk. These files are used to store data on disk. Database datafiles are only written to by the DBWR processes.

2)    Segments:-

A segment is a set of extents that contains all the data for a specific logical storage structure within a tablespace. For example, for each table, Oracle allocates one or more extents to form that table's data segment, and for each index, Oracle allocates one or more extents to form its index segment.

3)    Extend:-

An extent is a logical unit of database storage space allocation made up of a number of contiguous data blocks. One or more extents in turn make up a segment. When the existing space in a segment is completely used, Oracle allocates a new extent for the segment.

4)    Block:-

Oracle manages the storage space in the datafiles of a database in units called data blocks. A data block is the smallest unit of data used by a database. In contrast, at the physical, operating system level, all data is stored in bytes. Each operating system has a block size. Oracle requests data in multiples of Oracle data blocks, not operating system blocks.



Read Also:- Oracle Architecture