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ORACLE 11 g

ORACLE 11 g. ARCHITECTURE - I. 1. 1. Architecture - 1. INSTANCE. Every running Oracle database is associated with an Oracle instance.

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ORACLE 11 g

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  1. ORACLE 11g ARCHITECTURE - I 1 1

  2. Architecture - 1 INSTANCE • Every running Oracle database is associated with an Oracle instance. • When a database is started on a database server, Oracle allocates a memory area called the System Global Area (SGA), and starts some Oracle processes called background process (BP). • This combination of the SGA and the BP is called an Oracle instance. 1 1

  3. Architecture - 1 An Oracle instance runs two types of processes - Server and Background. Server processes are created to handle requests from sessions connected to the instance. Background processes, as the name says, are processes running behind the scene and are meant to perform certain maintenance activities or to deal with abnormal conditions arising in the lifetime of the instance. 1 1

  4. Architecture - 1 Not all background processes are mandatory for an instance. Each background process is meant for a specific purpose and its role is well defined. • We have two type of BG processes • Mandatory BG processes • Optional BG processes 1 1

  5. Architecture - 1 • User process Started at the time a database user requests connection to the Oracle server • Server process Connects to the Oracle Instance and is started when a user establishes a session • Background processes Started when an Oracle Instance is started 1 1

  6. Architecture - 1 Background processes • Background processes are invoked automatically when the instance is started. • Maintains and enforces relationships between physical and memory structures. • Mandatory background processes: • DBWn • PMON • CKPT • LGWR • SMON • RECO 1 1

  7. Architecture - 1 Optional Background Processes: • ARCn • LMDn • RECO • CJQ0 • LMON • Snnn • Dnnn • Pnnn • LCKn • QMNn 1 1

  8. Architecture - 1 • SGA contains the following data Structures • Database buffer cache • Redo log buffer • Shared pool (Library cache, Data dictionary cache) • Java pool • Large pool • Streams pool • Other miscellaneous information • Recycle pool 1 1

  9. Architecture - 1 System Global Area (SGA) is a group of shared memory structures that contain data and control information for one Oracle database instance. When multiple users are connected to the same instance, the data in the SGA is shared by all users. This is why it is called the Shared Global Area. 1 1

  10. Architecture - 1 • The Shared Pool portion of the SGA contains three memory structures : • The Library Cache • Data Dictionary • Control Structures. • The size of the Shared Pool can be customized using the parameter SHARED_POOL_SIZE 1 1

  11. Architecture - 1 • The database administrator can configure an • optional memory area called the large pool to • provide large memory allocations for • Session memory for the shared server and the Oracle XA interface (used where transactions interact with more than one database) • I/O server processes • Oracle backup and restore operations • Parallel execution message buffers. 1 1

  12. Architecture - 1 What are the free buffers in the database buffer cache? A. Buffers that have changed should be flushed to the disk. B. Buffers that are currently in use. C. Buffers that are being written to disk. D. Buffers that can be overwritten. Ans. D - Buffers that can be overwritten 1 1

  13. END OF CONCEPT ORACLE 11g - ARCHITECTURE - I 1 1

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