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Oracle Architectural Components:

Oracle Architectural Components


Objectives After completing this lesson, you should be able to do the following: Outline the Oracle architecture and its main components List the structures involved in connecting a user to an Oracle Instance

Overview of Primary Components:

Password file Overview of Primary Components Instance SGA Redo Log Buffer Shared Pool Data Dictionary Cache Library Cache DBWR SMON PMON CKPT LGWR Others User process Server process PGA Control files Datafiles Database Database Buffer Cache Redo Log files Java Pool Large Pool Parameter file Archived Log files

Oracle Server:

Oracle Server An Oracle server: Is a database management system that provides an open, comprehensive, integrated approach to information management Consists of an Oracle Instance and an Oracle database Oracle Server

Oracle Instance:

Oracle Instance An Oracle Instance: Is a means to access an Oracle database Always opens one and only one database Consists of memory and background process structures Background process structures Memory structures Instance SGA Redo Log Buffer Shared Pool Data Dictionary Cache Library Cache DBWR SMON PMON CKPT LGWR Others Database Buffer Cache Java Pool Large Pool

Establishing a Connection and Creating a Session:

Establishing a Connection and Creating a Session Connecting to an Oracle Instance: Establishing a user connection Creating a session Session created Database user User process Server process Connection established Oracle Server

Oracle Database:

Oracle Database An Oracle database: Is a collection of data that is treated as a unit Consists of three file types Password file Parameter file Archived Log files Control files Datafiles Redo Log files Oracle Database

Physical Structure :

Physical Structure The physical structure includes three types of files: Control files Datafiles Redo log files Control files Datafiles (includes Data Dictionary) Header Online Redo Log files

Memory Structure:

Memory Structure Oracle’s memory structure consists of two memory areas known as: System Global Area (SGA): Allocated at instance startup, and is a fundamental component of an Oracle Instance Program Global Area (PGA): Allocated when the server process is started

System Global Area:

System Global Area The SGA consists of several memory structures: Shared Pool Database Buffer Cache Redo Log Buffer Other structures (for example, lock and latch management, statistical data) There are two additional memory structures that can be configured within the SGA: Large Pool Java Pool

System Global Area:

System Global Area SGA is dynamic Sized by the SGA_MAX_SIZE parameter Allocated and tracked in granules by SGA components Contiguous virtual memory allocation Granule size based on total estimated SGA_MAX_SIZE

Shared Pool:

Shared Pool Used to store: Most recently executed SQL statements Most recently used data definitions It consists of two key performance-related memory structures: Library Cache Data Dictionary Cache Sized by the parameter SHARED_POOL_SIZE Shared Pool Data Dictionary Cache Library Cache ALTER SYSTEM SET SHARED_POOL_SIZE = 64M;

Library Cache:

Library Cache Stores information about the most recently used SQL and PL/SQL statements Enables the sharing of commonly used statements Is managed by a least recently used (LRU) algorithm Consists of two structures: Shared SQL area Shared PL/SQL area Size determined by the Shared Pool sizing

Data Dictionary Cache:

Data Dictionary Cache A collection of the most recently used definitions in the database Includes information about database files, tables, indexes, columns, users, privileges, and other database objects During the parse phase, the server process looks at the data dictionary for information to resolve object names and validate access Caching data dictionary information into memory improves response time on queries and DML Size determined by the Shared Pool sizing

Database Buffer Cache:

Database Buffer Cache Stores copies of data blocks that have been retrieved from the datafiles Enables great performance gains when you obtain and update data Managed through an LRU algorithm DB_BLOCK_SIZE determines primary block size Database Buffer Cache

Database Buffer Cache:

Database Buffer Cache Consists of independent sub-caches: DB_CACHE_SIZE DB_KEEP_CACHE_SIZE DB_RECYCLE_CACHE_SIZE Can be dynamically resized DB_CACHE_ADVICE set to gather statistics for predicting different cache size behavior Statistics displayed by V$DB_CACHE_ADVICE ALTER SYSTEM SET DB_CACHE_SIZE = 96M;

Redo Log Buffer:

Redo Log Buffer Records all changes made to the database data blocks Primary purpose is recovery Changes recorded within are called redo entries Redo entries contain information to reconstruct or redo changes Size defined by LOG_BUFFER Redo Log Buffer

Large Pool:

Large Pool An optional area of memory in the SGA Relieves the burden placed on the Shared Pool Used for: Session memory (UGA) for the Shared Server I/O server processes Backup and restore operations or RMAN Parallel execution message buffers PARALLEL_AUTOMATIC_TUNING set to TRUE Does not use an LRU list Sized by LARGE_POOL_SIZE

Java Pool:

Java Pool Services parsing requirements for Java commands Required if installing and using Java Sized by JAVA_POOL_SIZE parameter

Program Global Area:

Program Global Area Memory reserved for each user process connecting to an Oracle database Allocated when a process is created Deallocated when the process is terminated Used by only one process User process PGA Server process

Process Structure:

Process Structure Oracle takes advantage of various types of processes: 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

User Process:

User Process A program that requests interaction with the Oracle server Must first establish a connection Does not interact directly with the Oracle server Database user Server process User process Connection established

Server Process:

Server Process A program that directly interacts with the Oracle server Fulfills calls generated and returns results Can be Dedicated or Shared Server Connection established Session created Database user User process Server process Oracle server

Background Processes:

Background Processes Maintains and enforces relationships between physical and memory structures Mandatory background processes: DBWn PMON CKPT LGWR SMON Optional background processes: ARCn LMDn RECO CJQ0 LMON Snnn Dnnn Pnnn LCKn QMNn

Database Writer (DBWn):

Database Writer (DBWn) DBWn writes when: Checkpoint occurs Dirty buffers reach threshold There are no free buffers Timeout occurs RAC ping request is made Tablespace OFFLINE Tablespace READ ONLY Table DROP or TRUNCATE Tablespace BEGIN BACKUP Instance SGA Control files Datafiles Redo Log files Database DBWn Database Buffer Cache

Log Writer (LGWR):

Log Writer (LGWR) LGWR writes: At commit When one-third full When there is 1 MB of redo Every three seconds Before DBWn writes Instance SGA Control files Datafiles Redo Log files Database Redo Log Buffer DBWn LGWR

System Monitor (SMON):

System Monitor (SMON) Responsibilities: Instance recovery Rolls forward changes in redo logs Opens database for user access Rolls back uncommitted transactions Coalesces free space Deallocates temporary segments Control files Datafiles Redo Log files Database Instance SGA SMON

Process Monitor (PMON):

Process Monitor (PMON) Cleans up after failed processes by: Rolling back the transaction Releasing locks Releasing other resources Restarting dead dispatchers PGA area Instance SGA PMON

Checkpoint (CKPT):

Checkpoint (CKPT) Responsible for: Signaling DBWn at checkpoints Updating datafile headers with checkpoint information Updating control files with checkpoint information Control files Datafiles Redo Log files Database Instance SGA DBWn LGWR CKPT

Archiver (ARCn):

Archiver (ARCn) Optional background process Automatically archives online redo logs when ARCHIVELOG mode is set Preserves the record of all changes made to the database ARCn Archived Redo Log files Control files Datafiles Redo Log files

Logical Structure:

Logical Structure Dictates how the physical space of a database is used Hierarchy consisting of tablespaces, segments, extents, and blocks Tablespace Datafile Segment Blocks Extent Segment

Processing SQL Statements:

Processing SQL Statements Connect to an instance using: User process Server process The Oracle server components that are used depend on the type of SQL statement: Queries return rows DML statements log changes Commit ensures transaction recovery Some Oracle server components do not participate in SQL statement processing


Summary In this lesson, you should have learned how to: Explain database files: datafiles, control files, online redo logs Explain SGA memory structures: Database Buffer Cache, Shared Pool, and Redo Log Buffer Explain primary background processes: DBWn, LGWR, CKPT, PMON, SMON Explain the use of the background process ARCn Identify optional and conditional background processes Explain logical hierarchy

Practice 1 Overview:

Practice 1 Overview This practice covers the following topics: Review of architectural components Structures involved in connecting a user to an Oracle Instance

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