ORACLE Architechture.ppt

ORACLE 11g
ARCHITECTURE - 1
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Major Database Release Number
The first digit is the most general identifier. It represents a major new version of the
software that contains significant new functionality.
Database Maintenance Release Number
The second digit represents a maintenance release level. Some new features may also
be included.
Application Server Release Number
The third digit reflects the release level of the Oracle Application Server (OracleAS).
Component-Specific Release Number
The fourth digit identifies a release level specific to a component. Different
components can have different numbers in this position depending upon, for
example, component patch sets or interim releases.
Platform-Specific Release Number
The fifth digit identifies a platform-specific release. Usually this is a patch set. When
different platforms require the equivalent patch set, this digit will be the same across
the affected platforms.
Identifying Your Oracle Database Software Release

The Relational Model
In his seminal 1970 paper "A Relational Model of Data for Large Shared Data Banks," E.
F. Codd defined a relational model based on mathematical set theory. Today, the most
widely accepted database model is the relational model.
The relational model has the following major aspects:
Structures
Well-defined objects store or access the data of a database.
Operations
Clearly defined actions enable users to manipulate the data and structures of a
database.
Integrity rules
Integrity rules govern operations on the data and structures of a database.
A relational database stores data in a set of simple relations. A relation is a set of
tuples. A tuple is an unordered set of attribute values.
A table is a two-dimensional representation of a relation in the form of rows (tuples)
and columns (attributes). Each row in a table has the same set of columns. A relational
database is a database that stores data in relations (tables). For example, a relational
database could store information about company employees in an employee table, a
department table, and a salary table.
See Also:
http://portal.acm.org/citation.cfm?id=362685 for an abstract and link to Codd's paper

Oracle Database Standard Edition One Oracle Database Standard Edition One delivers
unprecedented ease of use, power, and performance for workgroup, department-level, and
Web applications. From single-server environments for small business to highly distributed
branch environments, Oracle Database Standard Edition One includes all the facilities
necessary to build business-critical applications.
Oracle Database Standard Edition Oracle Database Standard Edition delivers the
unprecedented ease of use, power, and performance of Standard Edition One, with support
for larger machines and clustering of services with Oracle Real Application Clusters (Oracle
RAC). Oracle RAC is not included in the Standard Edition of releases prior to Oracle Database
10g, nor is it an available option with those earlier releases.
Oracle Database Enterprise Edition Oracle Database Enterprise Edition provides the
performance, availability, scalability, and security required for mission-critical applications
such as high-volume online transaction processing (OLTP) applications, query-intensive data
warehouses, and demanding Internet applications. Oracle Database Enterprise Edition
contains all of the components of Oracle Database, and can be further enhanced with the
purchase of the options and packs described in Chapter 2, "Options and Packs".

Oracle Database Express Edition Oracle Database Express Edition (Oracle Database
XE) is an entry-level edition of Oracle Database that is quick to download, simple to
install and manage, and is free to develop, deploy, and distribute. Oracle Database XE
makes it easy to upgrade to the other editions of Oracle without costly and complex
migrations. Oracle Database XE can be installed on any size machine with any number
of CPUs, stores up to 4GB of user data, using up to 1GB of memory, and using only
one CPU on the host machine. Support is provided by an online forum.
Oracle Database Personal Edition Oracle Database Personal Edition supports single-
user development and deployment environments that require full compatibility with
Oracle Database Standard Edition One, Oracle Database Standard Edition, and Oracle
Database Enterprise Edition.

Oracle Architecture I
Objects Logical
Face
Database
Physical
Face
Files O.S
Tables
Views
Synonyms
Culsters
Tablespaces
Procedures
Functions
Etc.
Device Driv
Hardware
Disk
Controlfiles
Data files
Redolog files

Instance
SGA
Oracle 11g Architecture - I
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 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.
INSTANCE
Architecture
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 The Oracle server is an object-relational database
management system that provides and open,
comprehensive, integrated approach to information
management
Oracle Database Users
 Logging Directly from to the host
 Two-tiered (client-server) connection
 Three-tiered connection
Oracle 11g Architecture - I
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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.
Architecture
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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
Architecture
Before lass
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 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
Architecture
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 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
Background processes
Architecture
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Architecture
Optional Background Processes:
 ARCn
 LMDn
 RECO
 CJQ0
 LMON
 Snnn
 Dnnn
 Pnnn
 LCKn
 QMNn
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Instance
SGA
Background Processes
F Oracle Server consists of an Oracle Instance and an Oracle database.
An Oracle Instance consists of a memory structure called SGA
(System Global Area) and background processes used by an oracle
server to manage a database. An Oracle instance, which is identified by
setting ORACLE_SID at the operating system,can open and use only
one database at any point of time.
An Oracle Instance:
F Is a means to access an
Oracle database
F Always opens one and
only one database
Oracle Instance
Oracle 11g Architecture - II
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Instance
Background Process SGA
DBWR
LGWR
PMON
SMON
CKPT
RECO
Mandatory Optional
CTWR
CJQ
OPQO
ARCH
RVWR
Java Pool
Redo Log Buffer
Shared Pool
DB Buffer Cache
Large Pool
Streams Pool
Library Cache
Data Dictionary
Cache
Non-default Buffer
Cache
Keep Pool
Recycle Pool
Mandatory Optional
Oracle Instance
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System Global Area
The memory structures of an Oracle Instance are contained in
a memory region called SGA, which contains data and
control information for the Oracle Server. The SGA is
allocated in the virtual memory of the computer where the
Oracle server resides. The SGA comprises several memory
structures including:
F Shared Pool: used to store information such as the most recently
executed SQL and the most recently used data from the data dictionary.
F Database Buffer Cache: used to store the most recently used data.
F Redo Log Buffer: used to register changes made to the database using
the Instancec
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The Shared Pool
Instance
SGA
Library
Cache
Data
Dictionary
Cache
Shared Pool
F Size defined by SHARED_POOL_SIZE
F Library Cache contains statement text, parsed code,
and an execution plan
F Data Dictionary Cache contains table and column
definitions and privileges
F The shared pool is a part of the SGA that is used during the parse phase.
The size of the shared pool is defined by the initialization parameter
SHARED_POOL_SIZE in the parameter file.
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Library Cache
The Library Cache stores the following information about the
most recently used SQL statement:
F Text of the statement
F Parse tree, which is the compiled version of
the statement
F Execution Plan, which defines the steps to
be followed in running of the statement as
determined by the optimizer
Since, the library cache stores this information, if a query is
reexecuted before its execution plan is aged out by other statements,
the server process does not need to parse the statement. Thus the
library cache helps improve the performance of applications.
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Data Dictionary Cache
F The Data Dictionary Cache, also known as dictionary
cache or row cache is a part of the shared pool that
stores the most recently used data dictionary
information, such as table and column definitions,
usernames, passwords and privileges
F During the parse phase, the server process looks for the
information in the dictionary cache to resolve the object
names specified in the SQL statement and to validate
the access privileges. If necessary, the server process
initiates the loading this information from the datafiles
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Database Buffer Cache
Instance
SGA
F Number of buffers defined by DB_BLOCK_BUFFERS
F Size of a buffer based on DB_BLOCK_SIZE
F Stores the most recently used blocks
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Redo Log Buffer
Instance
SGA
F Size defined by LOG_BUFFER
F Records changes made through the instance
F Used sequentially
F Circular Buffer
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Redo Log Buffer
The server process records changes made by an instance in the Redo log
buffer, which is the part of the SGA. The Redo log buffer has following
characteristics.
F Its size in bytes is defined by the LOG_BUFFER parameter
F It stores redo records,which record changes - that is, the block that is
changed, the location of the change, and the new value. A redo entry
registers a change, but it makes more distinction between the type of
the block that is changed. So it cannot distinguish, for example, a
change to a data block from a change to an index or a rollback block
F The redo log buffer is used sequentially, and changes made by one
transaction may be interleaved with changes made by other
transactions
F It is a circular buffer that is reused after it is filled up,but only after
all the old redo entries are recorded in the redo log files.
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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.
Architecture
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Oracle Server
Instance
SGA
Data
Data
Data
Workstation
User Process
Server Process
User
Server
Connecting to a database
Oracle 11g Architecture - III
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Program Global Area (PGA)
Server
Process
PGA
F Not shared and not writable
F Contains
4 Sort Area
4 Session Information
4 Cursor state
4 Stack space
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Program Global Area (PGA)
The Program Global Area (PGA) is a memory region that contains data
and controls information for a single server process or a single
background process. In contrast to the SGA which is shared and written
to by several processes, the PGA which is also called the Process Global
Area, is an area that is used by only one process. When using the
dedicated server configuration the PGA contains:
H Sort area: which is used for any sort that may be necessary before
rows are processed or returned to the user
H Session Information: such as user privileges for the session
H Cursor state: which indicates the stage in the processing of various
cursors that are currently used by the session
H Stack space: containing the session variables
J The PGA is allocated when a process is created and deallocated when
the process is terminated
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Database Writer (DBWR)
Control Files
Data
Datafiles Redo Log files
Data
Data
Data
Data
Data
Instance
SGA
DBWR
Shared Pool
Database
Buffer
Cache
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F The server process records changes to rollback and data
blocks in the buffer cache. The database writer (DBWR)
writes the dirty buffers from the database buffer cache to
the datafiles. It ensures that sufficient no. of free buffers
- buffers that can be over written when server processes
need to read in blocks from the datafiles- are available in
the database buffer cache. Database performance is
improved because server processes only make changes
in the buffer cache, and the DBWR defers writing to the
datafiles until one of the following events occur.
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F The number of dirty buffers reaches a threshold value
F A process scans a specified number of blocks when
scanning for free buffers and cannot find any
F A timeout occurs
F A DBWR checkpoint can be triggered by various events
such as closing of the database (Check point is a means of
synchronizing the database buffer cache with the datafile
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Log Writer (LGWR)
F The Log Writer (LGWR) is a background process that writes entries
from the redo log buffer into the redo log files.
Instance
SGA
LGWR
Shared Pool
Redo
Log
Buffer
Control Files
Data
Datafiles
Redo Log files
Data Data
Data
Data
Data
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The LGWR performs sequential writes to the redo log files
under the following situations:
Log Writer (LGWR)
F When the redo log buffer is one-third full
F When a timeout occurs (every three seconds)
F Before DBWR writes modified blocks in the
database buffer cache to that datafiles
F When a transaction commits
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Log Switches & Checkpoints
Control Files
Data
Datafiles Redo Log files
Data Data
Instance
SGA
LGWR
Shared Pool
Redo
Log
Buffer
Data
Data
Data
Database
Buffer
Cache
DBWR CKPT ARCH
Archived Log
Files
Data
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Log Switches
F LGWR writes to the Online Redo Log files sequentially
that is when the current Online Redo Log group is filled
LGWR begins writing to the next group. When the last
available online redo log file is filled LGWR returns to
the first online redo log group and starts writing again
F A Log Switch is the event during which log writer stops
writing to one online redo log group and starts writing to
another
F When a Log Switch occurs an event called a check point
is initiated
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Checkpoint Process
In high-activity databases, CKPT can be used to handle
writing log sequence numbers to the datafile headers and
control file, alleviating LGWR of that responsibility.
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Checkpoint
F All dirty database buffers covered by the log being check pointed are
written to the datafiles by DBWR
F The checkpoint background process (CKPT) updates the headers of all
datafiles and control file to reflect that it has successfully completed.
During a check point:
Checkpoint can occur for all datafiles in database or for only specific
datafiles. A checkpoint occurs, for example, in the following situations:
F At every log switch
F When an instance has been shutdown with the normal, transactional,
or immediate option.
F When forced by setting the initialization parameters,
LOG_CHECKPOINT_INTERVAL and LOG_CHECKPOINT_TIMEOUT
F When manually requested by the database administrator
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SMON(System Monitor Process)
The usage and the function of this background process is two
fold
F In the event of an instance failure when the structures
and the processes that comprise the Oracle instance
cannot run -the SMON process handles recovery from
the instance failure
F The SMON process handles disk space management
issues on the database by taking smaller fragments of
space and coalescing or piecing them together
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PMON (Process Monitor Process)
F PMON watches the user processes on the database to
make sure that they work correctly. If for any reason a
user process fails during its connection to Oracle, PMON
will clean up the remnants of its activities and make sure
that any changes it may have made to the system are
"rolled back," or backed out of the database and reverted
to their original form.
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In Oracle databases using the distributed option, this
background process handles the resolution of distributed
transactions against the database.
RECO Recoverer Process (optional)

ARCH Archiver Process (optional)
In Oracle databases that archive their online redo logs, the
ARCH process handles automatically moving a copy of the
online redo log to a log archive destination.
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LCK0..LCK9 Lock Processes (Optional)
There can be as many as ten. In databases that use the
Parallel Server option, this background process handles
acquiring locks on remote tables for data changes.

Executes data reads from disk on behalf of user processes.
Access to Server processes can either be shared or dedicated,
depending on whether the DBA uses MTS or not.
In the MTS architecture, when users connect to the database,
they must obtain access to a shared server process via a
dispatcher process
S000..S999 (Server Process)
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This process acts as part of the Oracle MTS architecture to
connect user processes to shared server processes that will
handle their SQL processing needs. The user process comes
into the database via a SQL*Net listener, which connects the
process to a dispatcher. From there, the dispatcher finds the
user process a shared server that will handle interacting with
the database to obtain data on behalf of the user process.
D001..D999 Dispatcher Process (Optional)
Reference : http://docs.oracle.com/cd/E11882_01/server.112/e16508/intro.htm
http://www.siue.edu/~dbock/cmis565/module1-architecture.htm

ORACLE Architechture.ppt

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