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Segments in Oracle
There are 11 types of segments in Oracle 10g:
These types can be grouped into four segment classes:
In order to find out the size of the respective segments, use dba_segments (or user_segments, or all_segments).
A segment can either be created so that it can have an unlimited or limited number of extents.
Oracle keeps track of free blocks for each data segment.
The segment header is stored in the first block of the first extent. It contains:
The following SQL statements require a temporary segment if they cannot be completed in memory:
Temporary segments can be stored in any tablespace. However, it makes more sense to store temporary segments in a temporary tablespace.
SMON frees temporary segments.