Oracle Database Architecture: Files and Relationships

Perspectives of a Database

• Physical Perspective

  • Database is a collection of files
    • Types of files:
      • Data files
      • Redo log files
      • Control files
  • Control Files:
    • Contain metadata about the database structure
    • Include info such as database name, various files
    • Read during the instance mount
  • Redo Log Files:
    • Grouped into redo log groups
  • Data Files:
    • Integral to understanding how a database works

• Logical Perspective

  • Database is composed of table spaces
    • A table space contains data files
    • Creation of table spaces involves creating or adding data files
    • One data file belongs to one table space
    • One table space can have multiple data files
  • Inside a Table Space
    • Segments: Logical groupings for storing objects like tables, indexes, etc.
    • Extents: Divisions within segments
      • Contiguous blocks of data
    • Blocks: The smallest unit in the Oracle DB logical model
      • Size specified at database creation (options: 2K, 4K, 8K, 16K, 32K)

Data Block Sizes

• Specified during database creation
• Default sizes include:
  • 2K
  • 4K
  • 8K
  • 16K
  • 32K
• Data block consists of OS blocks (operating system blocks) within data files
  • One Oracle block = one or more OS blocks

Hierarchy and Relationships

• Logical Hierarchy:
  • Database → Table Spaces → Segments → Extents → Blocks
• Relationships
  • Table Space → Data Files
    • One data file linked to one table space
    • Table spaces can have multiple data files
  • Segments → Extents
    • A segment has multiple extents
    • Each extent can be in different data files within the same table space
  • Extents → Blocks
    • Contiguous Oracle blocks within extents
  • Data Blocks → OS Blocks
    • One or more OS blocks make up an Oracle data block

Summary

• Understanding Oracle database involves both physical and logical structures
• Physical files: data files, redo log files, control files
• Logical structures: table spaces, segments, extents, blocks
• Proper allocation and structuring are crucial for database efficiency