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Oracle Database Architecture Explained: Components, Memory Structures, Storage Structures

Understand the major architectural components of Oracle Database, including memory structures, background processes, and logical and physical storage structures.

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Oracle Database Architecture Explained: Components, Memory Structures, Storage Structures

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  1. Unit 1 Exploring the Oracle Database Architecture

  2. Objectives • After completing this lesson, you should be able to: • List the major architectural components of Oracle Database • Explain the memory structures • Describe the background processes • Correlate the logical and physical storage structures

  3. Oracle Database • The Oracle relational database management system (RDBMS) provides an open, comprehensive, integrated approach to information management

  4. Connecting to a Server Client Middle tier Server Multitier architecture shown

  5. Oracle Database Architecture: Overview Instance Others SMON PMON RECO SGA Shared pool Databasebuffercache Redo logbuffer Library cache Data dictionarycache PGA Serverprocess DBWn CKPT LGWR ARCn Database Userprocess Archived log files Control files Online redo log files Data files

  6. Userprocess Serverprocess Connection Connecting to the Database • Connection: Communication between a user process and an instance • Session: Specific connection of a user to an instance through a user process SQL> Select … Session User Session

  7. Interacting with an Oracle Database Instance Userprocess Serverprocess SGA Shared pool Databasebuffercache Redo logbuffer Library cache Data dictionarycache DBWn CKPT LGWR SMON PMON RECO Others ARCn User

  8. Userprocess Serverprocess Oracle Database Server Structures Instance Memory structures SGA Shared pool Databasebuffercache Redo logbuffer Library cache Data dictionarycache Processes DBWn CKPT LGWR SMON PMON ARCn RECO Others Database Storage structures Control files Online redo log files Data files

  9. Oracle Database Memory Structures DB structures Memory - Process - Storage Serverprocess 1 Serverprocess 2 Backgroundprocess PGA PGA PGA SGA Data dictionary cache Shared SQL area Other Library cache Shared pool Redo log buffer Free memory I/O buffer Database buffercache Response queue Request queue Java pool Streams pool Large pool

  10. Process Architecture DB structures - Memory Process - Storage • User process • Is started when a database user or a batch process connects to Oracle Database • Database processes • Server process: Connects to the Oracle instance and is started when a user establishes a session • Background processes: Are started when an Oracle instance is started Instance SGA Shared pool Databasebuffercache Redo logbuffer Library cache Data dictionarycache PGA Userprocess Serverprocess Background processes DBWn CKPT LGWR SMON PMON RECO Others ARCn

  11. Process Structures Server Server Server Server Server Server n processes SGA Shared pool Databasebuffercache Redo logbuffer Library cache SGA Data dictionarycache CKPT RECO PMON SMON DBWn LGWR ARCn Others Oracle background processes

  12. Database Writer Process (DBWn) • Writes modified (dirty) buffers in the database buffer cache to disk: • Asynchronously while performing other processing • Periodically to advance the checkpoint DBWn Database buffer cache Database writer process Data files

  13. LogWriter Process (LGWR) • Writes the redo log buffer to a redo log file on disk • Writes: • When a user process commits a transaction • When the redo log buffer is one-third full • Before a DBWn process writes modified buffers to disk LGWR Redo log buffer LogWriter process Redo log files

  14. Checkpoint Process (CKPT) • Records checkpoint information in • Control file • Each data file header CKPT Control file Checkpoint process Data files

  15. System Monitor Process (SMON) • Performs recovery at instance startup • Cleans up unused temporary segments SMON Instance System Monitor process Temporary segment

  16. Process Monitor Process (PMON) • Performs process recovery when a user process fails • Cleans up the database buffer cache • Frees resources that are used by the user process • Monitors sessions for idle session timeout • Dynamically registers database services with listeners PMON User Failed user process Process Monitor process Database buffer cache

  17. Recoverer Process • Used with the distributed database configuration • Automatically connects to other databases involved in in-doubt distributed transactions • Automatically resolves all in-doubt transactions • Removes any rows that correspond to in-doubt transactions RECO Recoverer processin database A In-doubt transactionin database B

  18. Archiver Processes (ARCn) • Copy redo log files to a designated storage device after a log switch has occurred • Can collect transaction redo data and transmit that data to standby destinations ARCn Archiver process Copies of redo log files Archive destination

  19. Database Storage Architecture DB structures - Memory - Process Storage Control files Data files Online redo log files Parameter file Backup files Archived redo log files Password file Alert log and trace files

  20. Logical and Physical Database Structures Logical Physical Database Data file Schema Tablespace Segment Extent OS block Oracle datablock

  21. Tablespaces and Data Files • Tablespaces consist of one or more data files. • Data files belong to only one tablespace. Data file 2 Data file 1 USERS tablespace

  22. SYSTEM and SYSAUX Tablespaces • The SYSTEM and SYSAUX tablespaces are mandatory tablespaces that are created at the time of database creation. They must be online. • The SYSTEM tablespace is used for core functionality (for example, data dictionary tables). • The auxiliary SYSAUX tablespace is used for additional database components (such as the Enterprise Manager Repository).

  23. Segments, Extents, and Blocks • Segments exist in a tablespace. • Segments are collections of extents. • Extents are collections of data blocks. • Data blocks are mapped to disk blocks. Segment Extents Data blocks Disk blocks

  24. Database Architecture:Summary of Structural Components • Memory structures: • System Global Area (SGA): Database buffer cache, redo buffer, and various pools • Program Global Area (PGA) • Process structures: • User process and server process • Background processes: SMON, PMON, DBWn, CKPT, LGWR, ARCn, and so on • Storage structures: • Logical: Database, schema, tablespace, segment, extent, and Oracle block • Physical: Data files, control files, and redo log files

  25. Summary • In this lesson, you should have learned how to: • List the major architectural components of Oracle Database • Explain the memory structures • Describe the background processes • Correlate the logical and physical storage structures

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