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Storage - Oracle Architecture

Logical Storage

 Blocks

 Data Block is the smallest unit of logical storage for a database object.

 Extents

 Extends is the next level of logical grouping in the database. An extent contains one or more database blocks.

 Segments

 The next level of logical grouping in a database in the segments. A segment is a group of extents from a database object that Oracle treats as a unit.
  • Data Segments: Every table in the database resides in a single data segment, consisting of one or more extents.
  • Index Segments: Each index is stored in its own index segment. As with partitioned tables, each partition of a partitioned index is stored in its own segment.
  • Temporary Segments: When a user's SQL statement needs disk space to complete an operation such as a sorting operation that cannot fit in memory, Oracle allocates a temporary segment. Temporary segments exist only for the duration of SQL execution.
  • Rollback Segments: Rollback Segments only exists in the SYSTEM tablespace, and typically the DBA doesn't need to maintain the SYSTEM rollback segment.


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