Re: What is an extent ?

aak2_at_Ra.MsState.Edu (Atif Ahmad Khan) wrote:
>
>SQL reference manual talks about how to increase and decrease the number of
>extents but doesn't actually say what it is. Looks like short for "extensions"
>Maybe not. (Minimum extensions, maximum extensions) doesn't make sense.
>I looked up "extent" in webter and their description of the word extent doesn't
>seem fitting either. Any ideas ?
>
>Thanks.
>
>Atif Khan
>aak2_at_ra.msstate.edu

Hi there,

Oracle stores all the database objects in the following groupings.

1. Segments
2. Extents
3. Blocks

Blocks are the smallest storage unit of data. Group of database blocks form an extent and group of extents form a segment.

For example, a data segment is made up of number of database extents which in turn is made of large number of database blocks.

When you create a table, Oracle prompts you to specify the following

INITIAL_EXTENT
NEXT_EXTENT
MIN_EXTENTS
MAX_EXTENTS If you do not specify, it is taken from default tablespace storage options.

What they all means

INITIAL_EXTENT : When you create a table, Oracle allocates that much database blocks for that table. Basically it reserves the space in advance.

NEXT_EXTENT : When the first initial extent is occupied completely, Oracle dynamically adds the NEXT_EXTENT value.

MIN_EXTENTS : This specifies Oracle how much EXTENTS should be allocated at the time of creation.

MAX_EXTENTS : This specifies the maximum number of EXTENTS that can ever be allocated to this database object. Beyond which Oracle will give error message MAX EXTENTS reached for the object.

Hope the above info helps

Regards

N.Prabhakar Received on Wed Nov 20 1996 - 00:00:00 CST