Transcript Basic_Oracle_Architecture

Basic Oracle Architecture
Presented to HIOUG
21-Jun-2005
By Byron Bush
Workshop Objectives
• Identify high-level architectural
components of an Oracle Database
• Describe the function of each of these
components
• Identify Oracle Database internal data
structures
• Define the mechanisms used when
processing Insert/Update/Delete
statements
Most people call it a “Database”
Technically an Oracle Database is broken
into two high-level components
1. INSTANCE – Non-persistent, memorybased processes and structures
2. DATABASE – Persistent, disk-based data
and control files
So Why Differentiate?
Most Oracle installations consist of only a
single “Instance” and single “Database”…
Instance
Database
Oracle RAC is Different
Oracle “Real Application Clusters” allow
multiple “Instances” to interact with a
single “Database” to provide high
availability…
Instance 1
Instance 2
Database
Instance 3
“Instance” a Little Closer
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
Picture of an “Instance”
Instance
SGA
Shared Pool
Library
Cache
Database Buffer
Cache
Data
Dictionary
Cache
Java Pool
PMON
SMON
Redo Log
Buffer
Memory
Structures
DBWR
LGWR
Large Pool
CKPT
Others
BackGround
Processes
“Database” a Little Closer
An Oracle Database…
– Is a collection of data that is treated as a unit
– Consists of three file types
Picture of a “Database”
Oracle Database
Data Files
Parameter
File
Password
File
Control Files
Redo Log Files
Archived
Log Files
Picture of an “Instance”
Instance
SGA
Shared Pool
Library
Cache
Database Buffer
Cache
Data
Dictionary
Cache
Java Pool
PMON
SMON
Redo Log
Buffer
Memory
Structures
DBWR
LGWR
Large Pool
CKPT
Others
BackGround
Processes
Memory Structure
Oracle’s memory structure consists of two
memory areas known as:
1. System Global Area (SGA): Allocated at
instance start up, and is a fundamental
component of an Oracle Instance
2. Program Global Area (PGA): Allocated
when the server process is started
System Global Area
• The SGA consists of several memory structures:
–
–
–
–
Shared Pool
Database Buffer Cache
Redo Log Buffer
Other structures
• There are two additional memory structures that
can be configured within the SGA:
– Large Pool
– Java Pool
System Global Area
• The size of the SGA is determined by the
parameters that set the sizes of the
various pools; these parameters are
dynamic
• The SGA_MAX_SIZE parameter sets the
maximum size of the SGA (so you can
limit it) and is not a dynamic parameter
Thanks Ned!
Picture of an “Instance”
Instance
SGA
Shared Pool
Library
Cache
Database Buffer
Cache
Data
Dictionary
Cache
Java Pool
PMON
SMON
Redo Log
Buffer
Memory
Structures
DBWR
LGWR
Large Pool
CKPT
Others
BackGround
Processes
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
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 is determined by the Shared Pool sizing
Picture of an “Instance”
Instance
SGA
Shared Pool
Library
Cache
Database Buffer
Cache
Data
Dictionary
Cache
Java Pool
PMON
SMON
Redo Log
Buffer
Memory
Structures
DBWR
LGWR
Large Pool
CKPT
Others
BackGround
Processes
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
Database Buffer Cache
• Stores copies of data blocks that have
been retrieved from the data files
• Enables great performance gains when
you obtain and update data
• Managed through an LRU algorithm
• DB_BLOCK_SIZE determines primary
block size
Picture of an “Instance”
Instance
SGA
Shared Pool
Library
Cache
Database Buffer
Cache
Data
Dictionary
Cache
Java Pool
PMON
SMON
Redo Log
Buffer
Memory
Structures
DBWR
LGWR
Large Pool
CKPT
Others
BackGround
Processes
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
Large Pool
• An optional area of memory in the SGA
• Relieves the burden place on the Shared Pool
• Used for:
– Session memory for the Shared Server
– I/O server processes
– Backup and restore operations for RMAN
• Does not use an LRU list
• Sized by LARGE_POOL_SIZE
• Can be dynamically resized
Java Pool
• Services parsing requirements for Java
commands
• Required if installing and using Java
• Sized by JAVA_POOL_SIZE parameter
Oracle “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
• A program that requests interaction with the
Oracle server
• Must first establish a connection
• Does not interact directly with the Oracle server
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
Picture of an “Instance”
Instance
SGA
Shared Pool
Library
Cache
Database Buffer
Cache
Data
Dictionary
Cache
Java Pool
PMON
SMON
Redo Log
Buffer
Memory
Structures
DBWR
LGWR
Large Pool
CKPT
Others
BackGround
Processes
Background Processes
• Maintains and enforces relationships
between physical and memory structures
– Mandatory background processes:
DBWn
LGWR
PMON
SMON
CKPT
– Optional background processes:
ARCn
CJQ0
Dnnn
LCKn
LMDn
LMON
LMS
Pnnn
QMNn
RECO
Snnn
Database Writer (DBWn)
Instance
DBWn writes when:
Shared
Shared Pool
Pool
SGA
Library
Cache
Database Buffer
Cache
Redo Log
Buffer
•
•
Data
Dictionary
Cache
Java Pool
Large Pool
•
PMON
SMON
DBWR
LGWR
CKPT
Others
Oracle Database
Data Files
Control Files
•
•
•
•
Redo Log Files
•
Checkpoint occurs
Dirty buffers reach
threshold
There are no free
buffers
Timeout occurs
Tablespace OFFLINE
Tablespace READ
ONLY
Table DROP or
TRUNCATE
Tablespace BEGIN
BACKUP
Log Writer (LGWR)
Instance
LGWR writes:
Shared Pool
SGA
Library
Cache
Database Buffer
Cache
Redo Log
Buffer
Data
Dictionary
Cache
Java Pool
Large Pool
PMON
SMON
DBWR
LGWR
Oracle Database
Data Files
Control Files
Redo Log Files
CKPT
•
•
•
Others
•
•
At commit
When one-third full
When there is 1 MB of
redo
Every three seconds
Before DBWn writes
System Monitor (SMON)
Instance
Responsibilities:
Shared
Shared Pool
Pool
SGA
Library
Cache
Database Buffer
Cache
Redo Log
Buffer
Data
Dictionary
Cache
Java Pool
Large Pool
PMON
SMON
DBWR
LGWR
Oracle Database
Data Files
Control Files
Redo Log Files
CKPT
•
Instance recovery
– Rolls forward
changes in online
redo log files
– Opens database for
user access
– Rolls back
uncommitted
transactions
Others
•
•
Coalesces free space
Deallocates temporary
segments
Process Monitor (PMON)
Instance
Shared
SharedPool
Pool
SGA
Library
Cache
Database Buffer
Cache
Redo Log
Buffer
Data
Dictionary
Cache
Java Pool
Large Pool
PMON
SMON
DBWR
LGWR
Oracle Database
Data Files
Control Files
Redo Log Files
CKPT
Cleans up after failed
processes by:
•
•
•
Others
•
Rolling back the
transaction
Releasing locks
Releasing other
resources
Restarting dead
dispactchers
Checkpoint (CKPT)
Instance
Responsible for:
Shared
SharedPool
Pool
SGA
Library
Cache
Database Buffer
Cache
Data
Dictionary
Cache
Java Pool
•
Redo Log
Buffer
•
Large Pool
•
PMON
SMON
DBWR
LGWR
CKPT
Others
Oracle Database
Data Files
Control Files
Redo Log Files
Signaling DBWn at
checkpoints
Updating datafile
headers with
checkpoint information
Updating control files
with checkpoint
information
Archiver (ARCn)
• Optional background process
• Automatically archives online redo log files when
ARCHIVELOG mode is set
• Preserves the record of all changes made to the
database
Oracle Database
Data Files
Control Files
Redo Log Files
Archived Logs
ARCn
Oracle Data Storage
Oracle keeps all system and user data in
two basic storage containers:
1. Tablespace… a logical entity known only
to Oracle
2. Data Files… physical files that may
(typically) be seen from the operating
system
Tablespaces
• Can belong to only one database at a time
• Consist of one or more data files
• Are further divided into logical units of
store
Data Files
• Can belong to only one tablespace and
one database
• Are a repository for schema object data
Database
Tablespace
Data
File
Data
File
2 Types of Tablespace
1. Tablespaces required by Oracle for
normal operations
2. Tablespaces that contain data and
indexes that support your applications
Required Tablespaces
• System – Contains the Oracle Data
Dictionary
• Sysaux - New to 10g; supports historic
monitoring / tuning
• Temporary – Used for disk-based sorting
of data (select...from…order by)
• Undo – Used for transaction consistency
during Insert / Update / Delete statements
SQL Statements (IUDS)
•
•
•
•
Insert
Update
Delete
Select
What happens when
someone connects to
the database and
issues one of these
statements?
Connect to Oracle – What Happens
User
Process
Connect User/Pwd
Server
Process
• Are “User” definition and privileges in SGA
“Dictionary Cache”?
– If not, try to fetch from the “System”
tablespace
– If there, validate Pwd and privileges to login
– Allow connection if all is right; otherwise
decline connection
“Select” – What Happens First?
Select *
From MyTab
Order by 1;
• Is this statement in the “Library Cache”?
– If statement cached then it has been recently
been “parsed” and “executed”
– If not cached then “parse” the statement
– If cached then skip parsing stage and execute
statement
“Select” – Parsing the Statement
Select *
From MyTab
Order by 1;
• Does “MyTab” exist?
• Does user have Privs to select from
“MyTab”
• What columns are in “MyTab”
• What is the first column in “MyTab”
“Select” – Executing the Statement
Select *
From MyTab
Order by 1;
• Is “MyTab” data in the SGA “Buffer Cache”?
– If not, fetch data into Buffer Cache
• Sort data in “MyTab” by the first column
– If can sort records in memory then do so
– If cannot sort in memory then use “Temporary”
tablespace as disk-based staging area
• Return records to client process
“I/U/D” – What Happens First?
Insert (a,b,c)
Into MyTab;
• Is this statement in the “Library Cache”?
– If statement cached then it has been recently
been “parsed” and “executed”
– If not cached then “parse” the statement
– If cached then skip parsing stage and execute
statement
“I/U/D” – Executing the Statement
Insert (a,b,c)
Into MyTab;
• Validate values to be inserted
• Execute the statement
– Keep DB version of the record in “Undo”
tablespace until Commit or Rollback
– Record changes in SGA “Redo Log Buffer”
– Change records in SGA “Buffer Cache”
– DBWn writes changed records to data file(s)
as part of buffer cache management
“I/U/D” – Executing the Statement
Insert (a,b,c)
Into MyTab;
Commit;
or
Rollback;
• If “Commit” then…
– LGWn writes “Redo Log Buffer” entries to
“Redo Logs”
– Undo entries are invalidated
• If “Rollback” then…
– Migrate DB version of record in Undo back to
tablespace/data file
Archivelog Mode
• If Instance in “Archivelog” mode Redo Log
Files are “Archived” to Archive Logs; which
may be used to recover your database in
the case of disaster
Oracle Database
Data Files
Control Files
Redo Log Files
Archived Logs
ARCn
Summary
• What we called a “Database” is really an
“Instance” and a “Database.”
• An Oracle “Instance” is not persistent. It consists
of the System Global Area (SGA) and a
collection of processes.
• An Oracle “Database” is persistent. It consists of
a collection of “Required” and “User”
tablespaces (with corresponding data files)
along with other supporting files.
• Nearly every component of the “Instance” and
“Database” are mobilized to execute SQL
statements.