Database Architecture Overview
Oracle 11g Server Architecture
•
•
•
•
•
•
•
•
Oracle Instance
Oracle Database
Database Files
Server Processes
Memory Structures
Transactions
Data Dictionary
Schema And Users
Oracle Server Architecture
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
Overview of Primary Components
User
process
Instance
Shared pool
Library
cache
Server
process
Data Dict.
cache
SGA
Redo log
Database
buffer cache buffer cache
PGA
PMON SMON DBWR LGWR
Parameter
file
Password
file
Data
files
Control
files
CKPT
Redo log
files
Database
Others
Archived
log files
Oracle 11g Server Architecture
•
•
•
•
•
•
•
Oracle Instance
Oracle Database
Database Files
Server Processes
Memory Structures
Data Dictionary
Schema And Users
Oracle Instance
• Is a means to access an Oracle database
• Always opens one and only one database
• Consists of memory and process structures
Instance
Shared pool
Library
cache
Data Dictionary
cache
SGA
Database
Redo log
buffer cache buffer cache
PMON SMON DBWR LGWR CKPT Others
Memory
structures
Background
structures
Oracle 11g Server Architecture
•
•
•
•
•
•
•
Oracle Instance
Oracle Database
Database Files
Server Processes
Memory Structures
Data Dictionary
Schema And Users
Physical Structure
The physical structure of an Oracle database is
determined by the operating system files that
provide the actual physical storage for database
information.
• Control files
• Data files
Header
Control
• Redo log files
Online
redo log
files)
Data files
(includes
data
dictionary)
files
Oracle 11g Server Architecture
•
•
•
•
•
•
•
Oracle Instance
Oracle Database
Database Files
Server Processes
Memory Structures
Data Dictionary
Schema And Users
Database Files
•
•
•
•
•
Parameter Files
Control Files
Data Files
Redo Log Files
Undo Data Files
Oracle Database
Oracle Database
Parameter
file
Password
file
Data
files
Control
files
Redo
log files
Archived
log files
Database Files
•
•
•
•
•
Parameter Files
Control Files
Data Files
Redo Log Files
Undo Data Files
Parameter Files
• Entries are specific to the instance being accessed
• There are two kinds of parameters:
• Explicit: Having an entry in the file
• Implicit: No entry within the file, but assuming the Oracle
default values
• Multiple files can be used for a single database to
optimize performance in different situations.
SPFILE spfileSID.ora
• Binary file with the ability to make changes
persistent across shutdown and startup
• Maintained by the Oracle server
• Records parameter value changes made with
the ALTER SYSTEM command
• Can specify whether the change being made is
temporary or persistent
• Values can be deleted or reset to allow an
instance to revert to the default value
• Can be dumped to text file for manual editing
Database Files
•
•
•
•
•
Parameter Files
Control Files
Data Files
Redo Log Files
Undo Data Files
Control File
The control file is a binary file that defines the
current state of the physical database..
• Loss of the control file requires recovery
• Is read at MOUNT stage
• Is required to operate
• Is linked to a single database
• Should be multiplexed
• Maintains integrity of database
• Sized initially by
CREATE DATABASE
Database
Control
files
Database Files
•
•
•
•
•
Parameter Files
Control Files
Data Files
Redo Log Files
Undo Data Files
Database Files
• Parameter Files
• Control Files
• Data Files
•
•
•
•
•
•
Tablespaces
Oracle Managed Files
Data Block
Data Types
Tables
Indexes
• Redo Log Files
• Undo Data Files
Logical Structure
The logical structure of the Oracle architecture
dictates how the physical space of a database is to be used.
A hierarchy exists in this structure that consists of
tablespaces, segments, extents, and blocks.
Tablespace
Data file
Segment
Extent
Segment
Blocks
SYSTEM and Non-SYSTEM Tablespaces
• SYSTEM tablespace:
•
•
•
Created with the database
Contains the data dictionary
Contains the SYSTEM undo segment
• Non-SYSTEM tablespaces:
•
•
•
Separate segments
Ease space administration
Control amount of space allocated to a user
Database Files
• Parameter Files
• Control Files
• Data Files
•
•
•
Tablespaces
Oracle Managed Files
Data Block
• Data Types
• Tables
• Indexes
• Redo Log Files
• Undo Data Files
Oracle Managed Files
• Oracle Managed Files (OMF) simplify file
administration by eliminating the need to directly
manage the files in an Oracle database
• This feature has two major thrusts:
•
•
Allows database objects to be created without
specifying the underlying operating system files
Automatically removes obsolete data files and online
redo logs
Database Files
• Parameter Files
• Control Files
• Data Files
•
•
•
•
•
•
Tablespaces
Oracle Managed Files
Data Block
Data Types
Tables
Indexes
• Redo Log Files
• Undo Data Files
Database Block
• Minimum unit of I/O
• Consists of one or more OS blocks
• Set at tablespace creation
• DB_BLOCK_SIZE is the default block size
Database Files
• Parameter Files
• Control Files
• Data Files
•
•
•
•
•
•
Tablespaces
Oracle Managed Files
Data Block
Data Types
Tables
Indexes
• Redo Log Files
• Undo Data Files
Oracle data types
Data type
User-defined
Scalar
CHAR(N), NCHAR(N)
VARCHAR2(N),
NVARCHAR2(N)
NUMBER(P,S)
DATE
RAW(N)
BLOB, CLOB,
NCLOB, BFILE
LONG, LONG RAW
ROWID
Built-in
Collection
VARRAY
TABLE
Relationship
REF
System-Provided Datatypes
Built-In Datatype
Native Datatypes
CHARACTER
NUMBER
Extended Datatypes
Support Datatypes
Text
ANSI
Image
DB2
DATE
Video
SQL/DS
LOB
RAW
ROWID
Audio
PL/SQL Datatypes
Spatial
BOOLEAN
XML
Time Series
BINARY_INTEGER
Database Files
• Parameter Files
• Control Files
• Data Files
•
•
•
•
•
•
Tablespaces
Oracle Managed Files
Data Block
Data Types
Tables
Indexes
• Redo Log Files
• Undo Data Files
Tables in Oracle
Regular table
Index-organized
table
Partitioned
table
Cluster
Database Files
• Parameter Files
• Control Files
• Data Files
•
•
•
•
•
•
Tablespaces
Oracle Managed Files
Data Block
Data Types
Tables
Indexes
• Redo Log Files
• Undo Data Files
Classification of Indexes
• Logical
•
•
•
•
Single column or concatenated
Unique or nonunique
Function Based
Domain Based
• Physical
• Partitioned or nonpartitioned
• B-tree
• Normal or reverse key
• Bitmap
• Bitmap Join Index
Database Files
•
•
•
•
•
Parameter Files
Control Files
Data Files
Redo Log Files
Undo Data Files
Using Redo Log Files
Redo log files record all changes made to data and
provide a recovery mechanism from a system or
media failure.
• Redo log files are organized into groups.
• An Oracle database requires at least two groups.
• Each redo log within a group is
called a member.
Database
Redo
log files
Structure of Redo Log Files
Group 1
Group 2
Group 3
Disk 1
Member
Member
Member
Member
Member
Member
Disk 2
How Redo Logs Work
• Redo logs are used in a cyclic fashion.
• When a redo log file is full, LGWR will move to the
next log group.
• This is called a log switch
• Checkpoint operation also occurs
• Information is written to the control file
Database Files
•
•
•
•
•
Parameter Files
Control Files
Data Files
Redo Log Files
Undo Data Files
Undo Data Overview
• Before Oracle makes a change to a database
block it is copied to the Undo area.
• Used for Rollback and Read Consistency.
Oracle 11g Server Architecture
•
•
•
•
•
•
•
•
Oracle Instance
Oracle Database
Database Files
Server Processes
Memory Structures
Transactions
Data Dictionary
Schema And Users
Process Structure
An Oracle process is a program that depending on its
type can request information, execute a series of
steps, or perform a specific task.
On some OS (MS Windows…) these are actually implemented as
process threads.
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 process: Available when an Oracle instance is
started
Background Processes
The relationship between the physical and memory
structures is maintained and enforced by Oracle’s
background processes.
• Mandatory background processes
DBWn
LGWR
PMON
SMON
CKPT
and others
• Optional background processes
ARCn
QMNn
CJQ0
LCKn
LMON
LMDn
Pnnn
Dnnn
Snnn
RECO
and others
Oracle 11g Server Architecture
•
•
•
•
•
•
•
•
Oracle Instance
Oracle Database
Database Files
Server Processes
Memory Structures
Transactions
Data Dictionary
Schema And Users
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 (SGA)
• The SGA consists of several memory structures:
• Shared pool
• Database buffer cache
• Redo log buffer
• Other structures (e.g. lock and latch
management, statistical data)
System Global Area (SGA)
• SGA is dynamic and sized using MEMORY_TARGET without
shutting down the instance
• SGA memory allocated and tracked in granules by SGA
components
• Contiguous virtual memory allocation
• Size based on MEMORY_TARGET
Program Global Area (PGA)
The PGA is memory reserved for each user process
that connects to an Oracle database.
Managed as part of the MEMORY_TARGET
PGA
Server
process
Dedicated server
Session
Stack
information
space sort area, cursor
information
User
process
SGA
Shared server
Stack sort area, cursor
information
space
SGA
Session
information
Shared SQL areas
Shared SQL areas
Oracle 11g Server Architecture
•
•
•
•
•
•
•
•
Oracle Instance
Oracle Database
Database Files
Server Processes
Memory Structures
Transactions
Data Dictionary
Schema And Users
Transactions
• Oracle has an implicit transaction model.
• A transaction starts immediately after the last one
completes
• Can be made READ-ONLY via ALTER
TRANSACTION command
• COMMIT or ROLLBACK ends transaction
Oracle’s Multi-Version Concurrency
Read Consistent Row Locking
With Oracle …
report
• Updates don’t lockout reports and
reports don’t lockout updates
Budget Table
• Reports see only committed data
via Multi-Versioning
update
Undo
Tablespace
Before
Image
accurate
report
• Queries yield maximum
throughput with correct results no waiting and no dirty reads!
• Row locks never escalate - the
most scaleable solution available
Multi Version Read Consistency High
Throughput Concurrency
Performance Table stakes
Oracle
Microsoft
Sybase
Unique Concurrency Model
Yes
No
No
Readers Don’t Block Writers
Yes
No*
No
Writers Don’t Block Readers
Yes
No*
No
Guarantees Consistent Queries
Yes
Yes
No
Eliminates Lock Escalation
Yes
No
No
Reduces Deadlocks under Load
Yes
No
No
Oracle does not compromise data accuracy for greater concurrency
*Except when using Snapshots in SS 2005
Oracle 11g Server Architecture
•
•
•
•
•
•
•
•
Oracle Instance
Oracle Database
Database Files
Server Processes
Memory Structures
Transactions
Data Dictionary
Schema And Users
Data Dictionary
During database creation, the Oracle server creates
additional object structures within the data files.
• Data dictionary tables
• Dynamic performance tables
Data
files
Control
files
Redo
log
files
Database
Data Dictionary Tables
Dynamic Performance Tables
Data Dictionary
The data dictionary is a set of read-only tables and
views that record, verify, and provide information
about its associated database.
• Describes the database and its objects
• Includes two types of objects:
• Base tables
• Store description of database
• Created with CREATE DATABASE
• Data Dictionary views
• Summarize base table information
• Created using catalog.sql script
Data Dictionary Contents
The data dictionary provides information about:
• Logical and physical database structure
• Definitions and space allocations of objects
• Integrity constraints
• Users
• Roles
• Privileges
• Auditing
Data Dictionary View Categories
The data dictionary consists of three main sets of
static views distinguished from each other by their
scope:
• DBA: What is in all the schemas
• ALL: What the user can access
• USER: What is in the user's schema
DBA_xxx
All of the objects in the database
ALL_xxx
Objects accessible by the current user
USER_xxx
Objects owned by the current user
Oracle 11g Server Architecture
•
•
•
•
•
•
•
Oracle Instance
Oracle Database
Database Files
Server Processes
Memory Structures
Data Dictionary
Schema And Users
Database Schema
•
•
•
•
•
A schema is a named
collection of objects
A user is created, and a
corresponding schema
can be created
User can be associated
only with one schema
Username and schema
are often used
interchangeably
Users are not
necessarily associated
with a schema
Schema Objects
Tables
Triggers
Constraints
Indexes
Views
Sequences
Stored program units
Synonyms
User-defined data types
Database links
Oracle 11g Server Architecture
• An Oracle server consists of an Oracle instance and
an Oracle database
• An Oracle instance consists of several required and
some more optional processes (threads)
• An Oracle database is built using different file types
QUESTIONS
ANSWERS