Oracle Architecture Components
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Transcript of Oracle Architecture Components
Oracle Architecture -1
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L&D - IRM
Oracle Architectural Components
Oracle Architecture -2
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Objectives
After completing this lesson, you should be able to do the following:Outline the Oracle architecture and its main
componentsList the structures involved in connecting a user
to an Oracle Instance
Oracle Architecture -3
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Passwordfile
Overview of Primary ComponentsInstance
SGA
Redo LogBuffer
Shared Pool
Data DictionaryCache
LibraryCache
DBWRSMONPMON CKPTLGWR Others
Userprocess
Serverprocess
PGA
Control files
Datafiles
Database
DatabaseBuffer Cache
Redo Log files
Java Pool Large Pool
Parameterfile
Archived Log files
Oracle Architecture -5
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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 Architecture -6
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Oracle Instance
An Oracle Instance:Is a means to access an Oracle databaseAlways opens one and only one databaseConsists of memory and background process structures
Background process structures
Memory structures
Instance
SGA
Redo LogBuffer
Shared Pool
Data DictionaryCache
LibraryCache
DBWRSMONPMON CKPTLGWR Others
DatabaseBuffer Cache
Java Pool Large Pool
Oracle Architecture -7
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Establishing a Connection and Creating a Session
Connecting to an Oracle Instance: Establishing a user connection Creating a session
Session created
Database user
Userprocess
ServerprocessConnection
established
Oracle Server
Oracle Architecture -9
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Oracle Database
An Oracle database:Is a collection of data that is treated as a unitConsists of three file types
Passwordfile
Parameterfile
Archived Log files
Control files
Datafiles Redo Log files
Oracle Database
Oracle Architecture -10
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Physical Structure
The physical structure includes three types of files:Control filesDatafilesRedo log files
Controlfiles
Datafiles(includes
Data Dictionary)
Header
OnlineRedo Log
files
Oracle Architecture -11
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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
Oracle Architecture -12
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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
Oracle Architecture -14
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System Global Area
SGA is dynamicSized by the SGA_MAX_SIZE parameterAllocated and tracked in granules by SGA
components Contiguous virtual memory allocation Granule size based on total estimated SGA_MAX_SIZE
Oracle Architecture -15
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Shared PoolUsed 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
DataDictionary
Cache
LibraryCache
ALTER SYSTEM SET SHARED_POOL_SIZE = 64M;
Oracle Architecture -16
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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
Oracle Architecture -17
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Data Dictionary CacheA collection of the most recently used definitions in the
databaseIncludes information about database files, tables, indexes,
columns, users, privileges, and other database objectsDuring 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
Oracle Architecture -18
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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 algorithmDB_BLOCK_SIZE determines primary block size
Database BufferCache
Oracle Architecture -19
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Database Buffer CacheConsists 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;
Oracle Architecture -21
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Redo Log BufferRecords all changes made to the database data
blocks Primary purpose is recoveryChanges recorded within are called redo entriesRedo entries contain information to reconstruct
or redo changesSize defined by LOG_BUFFER
Redo LogBuffer
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Large PoolAn optional area of memory in the SGA Relieves the burden placed on the Shared PoolUsed 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 listSized by LARGE_POOL_SIZE
Oracle Architecture -24
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Java Pool
Services parsing requirements for Java commandsRequired if installing and using JavaSized by JAVA_POOL_SIZE parameter
Oracle Architecture -25
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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
Userprocess
PGAServer
process
Oracle Architecture -28
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Process Structure
Oracle takes advantage of various types of processes:User process: Started at the time a database user
requests connection to the Oracle serverServer process: Connects to the Oracle Instance
and is started when a user establishes a sessionBackground processes: Started when an Oracle
Instance is started
Oracle Architecture -29
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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
Serverprocess
Userprocess
Connectionestablished
Oracle Architecture -30
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Server Process
A program that directly interacts with the Oracle server Fulfills calls generated and returns resultsCan be Dedicated or Shared Server
Connection established Session created
Database user
Userprocess
Serverprocess
Oracle server
Oracle Architecture -31
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Background ProcessesMaintains and enforces relationships between physical
and memory structuresMandatory background processes:
DBWn PMON CKPT LGWR SMON
Optional background processes: ARCn LMDn RECO CJQ0 LMON Snnn Dnnn Pnnn LCKn QMNn
Oracle Architecture -32
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Database Writer (DBWn)DBWn writes when:
Checkpoint occursDirty buffers reach
thresholdThere are no free buffersTimeout occursRAC ping request is madeTablespace OFFLINETablespace READ ONLYTable DROP or TRUNCATE
Tablespace BEGIN BACKUP
Instance
SGA
Control files
Datafiles Redo Log files
Database
DBWn
DatabaseBufferCache
Oracle Architecture -33
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Log Writer (LGWR)
LGWR writes:At commit When one-third fullWhen there is 1 MB of
redoEvery three secondsBefore DBWn writes
Instance
SGA
Control files
Datafiles Redo Log files
Database
Redo Log
Buffer
DBWn LGWR
Oracle Architecture -34
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System Monitor (SMON) Responsibilities:
Instance recovery Rolls forward
changes in redo logs Opens database for
user access Rolls back
uncommitted transactions
Coalesces free spaceDeallocates temporary
segments
Control files
Datafiles Redo Log files
Database
InstanceSGA
SMON
Oracle Architecture -35
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Process Monitor (PMON)
Cleans up after failed processes by:
Rolling back the transaction
Releasing locksReleasing other resourcesRestarting dead
dispatchersPGA area
Instance
SGA
PMON
Oracle Architecture -36
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Checkpoint (CKPT)
Responsible for:Signaling DBWn at
checkpointsUpdating datafile headers
with checkpoint information
Updating control files with checkpoint information
Control files
Datafiles Redo Log files
Database
Instance
SGA
DBWn LGWR CKPT
Oracle Architecture -37
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Archiver (ARCn)
Optional background processAutomatically 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
Oracle Architecture -39
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Logical Structure
Dictates how the physical space of a database is usedHierarchy consisting of tablespaces, segments, extents,
and blocks
Tablespace
DatafileSegment
BlocksExtent
Segment
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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
Oracle Architecture -43
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Processing SQL Statements
Processing a query: Parse:
– Search for identical statement– Check syntax, object names, and
privileges– Lock objects used during parse– Create and store execution plan
Bind: Obtains values for variables Execute: Process statement Fetch: Return rows to user process
Oracle Architecture -45
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SummaryIn 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 ARCnIdentify optional and conditional background
processesExplain logical hierarchy
Oracle Architecture -48
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QUIZ1. Match the process with the taska. DBWR b. LGWR c. SMON d. PMON e. CKPT1. Assists with writing to the data file headers2. Responsible for instance recovery3. Cleans up after failed processes4. Records database changes for recovery purposes5. Writes dirty buffers to the data files
Answers:– 5– 4– 2– 3– 1
Oracle Architecture -49
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QUIZ
2 . Which one of the following memory areas is not part of the SGA?
a. Database Buffer Cache
b PGA
c Redo Log Buffer
d. Shared Pool
Answer: PGA
Oracle Architecture -50
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QUIZ
3. Which one of the following memory areas is used to cache the data dictionary information?
a Database Buffer Cacheb PGAc Redo Log Buffer d Shared Pool
Answer: D
Oracle Architecture -51
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QUIZ
4 . Which two of the following statements are true about the Shared Pool?
a. The Shared Pool consists of the Library Cache, Data Dictionary Cache, Shared SQL area, Java Pool, and Large Pool.
b. The Shared Pool is used to store the most recently executed SQL statements.
c. The Shared Pool is used for an object that can be shared globally.d . The Library Cache consist of the Shared SQL and Shared
PL/SQL areas.
Answer: B& D
Oracle Architecture -52
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QUIZ
5 .Which one of the following statements is true?a. An Oracle server is a collection of data consisting
of three file types.b. A user establishes a connection with the
database by starting an Oracle Instance.c. A connection is a communication pathway
between the Oracle server and theOracle Instance.
d. A session starts when a user is validated by the Oracle server.
Answer: D
Oracle Architecture -53
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QUIZ
6. The primary purpose of the Redo Log Buffer is to record all changes to the database data blocks.
a Trueb False
Answer : A
Oracle Architecture -54
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QUIZ
6. The PGA is a memory region that contains data and control information for multiple server processes or multiple background processes.
a Trueb False
Answer: B
Oracle Architecture -55
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QUIZ
7. Which of the following becomes available when an Oracle Instance is started?
a User processb Server processc Background processes
Answer : C
Oracle Architecture -56
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