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Exploring the Oracle Database Architecture

This lesson provides an overview of the Oracle Database architecture, including the major components, memory structures, and storage. Learn about the memory structures, background processes, and logical and physical storage structures of Oracle Database.

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Exploring the Oracle Database Architecture

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  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. Database Buffer Cache • Is part of the SGA • Holds copies of data blocks that are read from data files • Is shared by all concurrent users Instance SGA Shared pool Databasebuffercache Redo logbuffer Library cache Data dictionarycache • DBWn • CKPT • LGWR • SMON • PMON • RECO • Others • ARCn

  11. Redo Log Buffer • Is a circular buffer in the SGA • Holds information about changes made to the database • Contains redo entries that have the information to redo changes made by operations such as DML and DDL Instance SGA Shared pool Databasebuffercache Redo logbuffer Library cache Data dictionarycache • DBWn • CKPT • LGWR • SMON • PMON • RECO • Others • ARCn

  12. Shared Pool • Is a portion of the SGA • Contains: • Library cache • Shared SQL area • Data dictionary cache • Control structures Instance • Shared SQL area SGA Shared pool • Data dictionary cache Databasebuffercache Redo logbuffer Library cache Data dictionarycache • Library cache • Other • DBWn • CKPT • LGWR • SMON • PMON • RECO • Others • ARCn

  13. Allocation and Reuse of Memory in the Shared Pool • Server process checks the shared pool to see if a shared SQL area already exists for an identical statement. • Server process allocates a private SQL area on behalf of the session. • Data dictionary cache • Shared SQL area Serverprocess • Library cache • Other • Shared pool

  14. Large Pool • Provides large memory allocations for: • Session memory for the shared server and the Oracle XA interface • I/O server processes • Oracle Database backup and restore operations Databasebuffercache Redo logbuffer • Shared pool • Free memory • I/O buffer • Response queue • Request queue • Java pool • Streams pool • Large pool • Large pool

  15. Java Pooland Streams Pool • Java pool memory is used in server memory for all session-specific Java code and data in the JVM. • Streams pool memory is used exclusively by Oracle Streams to: • Store buffered queue messages • Provide memory for Oracle Streams processes • Java pool • Streams pool

  16. 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

  17. 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

  18. 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

  19. 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

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

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

  22. 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

  23. 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

  24. 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

  25. Other Processes • MMON: Performs manageability-related background tasks • MMNL: Performs frequent and lightweight manageability-related tasks • MMAN: Performs automatic memory management tasks • CJQ0: Runs user jobs used in batch processing • QMNC: Monitors the Streams Advanced Queuing message queues

  26. Server Process and Database Buffer Cache • Buffers: • Pinned • Clean • Free or unused • Dirty SGA Serverprocess Databasebuffercache • DBWn • Database writer process • Data files

  27. 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

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

  29. 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

  30. 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).

  31. 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

  32. 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

  33. SummaryPractice 1: Overview • 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 • This is a paper practice with questions about: • Database architecture • Memory • Processes • File structures

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