Segments, Extents, and Data Blocks
Oracle preallocates segments of data blocks as the physical storage for data structures such as tables, indexes, etc. Oracle reserves groups of logically contiguous data blocks from a data file for a data structure as extents. A segment is the collection of all the extents dedicated to a data structure. Figure 8-7 demonstrates the relationship between a table and its data segment, extents, and data blocks.
When you create a new data structure such as a table, you can indicate the tablespace in which you want to create the corresponding segment. Oracle then allocates data blocks from one or more of the data files in use by the target tablespace.
Types of Segments in an Oracle Database
An Oracle database can contain ...
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