Managing Oracle Database Segments
In Oracle Database 12c, segments are logical storage structures that contain the actual data for database objects such as tables, indexes, and clusters. Understanding and managing segments is crucial for optimizing database performance and storage utilization. This section will cover key concepts related to managing Oracle Database segments.
1. Segments
A segment is a collection of extents that are allocated for a specific database object. Each segment belongs to a single tablespace and is used to store the data for that object. Segments can be of different types, including table segments, index segments, and rollback segments.
Example: A table named "Employees" will have a corresponding table segment that stores all the data for that table. This segment is divided into multiple extents, which are the actual units of storage on disk.
2. Extents
An extent is a contiguous block of data blocks allocated for a segment. When a segment requires more space, it is allocated additional extents. Extents help in managing storage efficiently by allowing the database to allocate space in chunks rather than individual data blocks.
Example: If a table segment initially has one extent of 1MB, and the table grows, the database will allocate additional extents (e.g., another 1MB) to accommodate the new data. This process continues as the table size increases.
3. Data Blocks
Data blocks are the smallest units of storage in an Oracle database. Each data block corresponds to a specific number of bytes on disk. Segments are composed of multiple extents, and each extent is composed of multiple data blocks. Data blocks are where the actual data is stored.
Example: If the database block size is 8KB, each extent might contain multiple 8KB data blocks. When a new row is inserted into a table, it is stored in one of these data blocks within the table segment.
By understanding these key concepts, you can effectively manage segments in an Oracle Database 12c environment. This knowledge is essential for optimizing storage utilization, improving performance, and ensuring efficient data management.