Transcript M 1 DBMS S ORACLE

Fall 2012
ITEC 450
MODULE 1
DBMS STRATEGY AND ORACLE
ARCHITECTURE
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Database Administration Techniques and
Practices
ORGANIZATION’S DBMS STRATEGY
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It’s typical to run two or more DBMS products in
large and medium-sized organization
The organization should have the vision to
consolidate and minimize the number
Using an existing DBMS whenever it is possible
Once a DBMS is installed, removal can be
difficult: incompatibilities, conversion, special
features
Organization’s DBMS strategy is a join effort
from groups of DBA, Architect, App Dev, and
Business
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CHOOSING A DBMS: SELECTION DRIVERS
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A commercial off-the-shelf application package:
ERM, PeopleSoft, CRM
The latest and greatest technology: Web, Java,
.NET
DBMS performance: TPC benchmarks
Operating systems: Unix, Windows, Linux
Hardware platforms: HP, Sun, IBM, Dell
Total cost of ownership: license, people,
development, and maintenance support
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LEVELS OF DBMS ARCHITECTURE
Enterprise and Departmental DBMS
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Scalability and availability, high performance
Large database, concurrent users, multiprocessors
Examples: Oracle, DB2, SQL Server
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Personal DBMS: Access, Visual dBase, Personal
Oracle
Mobile DBMS: a special version of DBMS for
remote users who are not on the network all the
time.
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DBMS ARCHITECTURE COMPONENTS
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Disk: logical and physical database
structures
CPU: Operating system processes
Memory: shared and private memory
structures
Network: user access and process
interactions
Clustering: multiple computing systems
working together
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SECTION IMPORTANT NOTES
This section is Oracle specific.
Terms can be very different among
different DBMS’s (e.g. Oracle vs. SQL)
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Database (different)
Instances (different)
Schemas (common)
Segments (Oracle specific)
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ORACLE DATABASE AND INSTANCE
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An Oracle Database server consists of an Oracle
Database and one or more Oracle Database
instances.
 Database: all Oracle related files
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Data files – holding tables and indexes
 System files – System, Undo, Temp
 Physical and logical structures
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Instance: the combination of processes and
memory
Processes – background
 Memory – allocated to Oracle
 Running components – Instance is up
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ORACLE
DATABASE
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INSTANCE
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PHYSICAL DATABASE STRUCTURE
Main types of files – data files, control files, redo
log files, archived redo log files.
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Data files – database data, such as tables and indexes
Control files – Oracle structure information, such as database
name, data file names, time stamp of database
Redo log files – database change logs for recovery
Archived redo log files – offline copies of online redo log files
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Parameter files – SPFILE, init.ora
Administration files – alert.log, trace files, the
password files
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PHYSICAL DATABASE STRUCTURE
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LOGICAL STRUCTURE DETAILS
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Read Chapter 2 Oracle Database Concept
 Data block - the standard block size is determined by
the init parameter DB_BLOCK_SIZE.
 Extent - When you create a database object, you
allocate it an initial extent. When the object grows
more than the initial extent, Oracle will automatically
allocate next extent.
 Segment - Oracle calls all the space allocated to a
particular database object a segment, such as table or
index.
 Tablespace - A tablespace contains one or more
physical files; a data file belongs to one and only one
tablespace.
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LOGICAL & PHYSICAL DATABASE
STRUCTURE
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ONLINE REDO LOG FILES AND
ARCHIVE LOG FILES
Redo log files record changes to database data
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Online redo log files are open and available whenever
the database is up and running
 They capture details of DB transactions and
information about changes to DB including:
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Checkpoints
 Changes
 Data Manipulation Language (DML)
 Data Definition Language (DDL)
 Datafile changes
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A database should have at least three redo log
groups containing at least one file each
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ONLINE REDO LOG FILES AND
ARCHIVE LOG FILES
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PURPOSE OF REDO LOG FILES
Purpose: aid in database recovery
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Redo log files keep list of DB changes
If DB loses changes, recovery process restores them
Redo log files receive the change information before the
data files are updated
In minor failures (e.g., short power outage), redo log
files are automatically checked during DB startup, and
data is restored, from redo log files into data files
In major failures (e.g., loss of an entire disk), data
would not be saved from the online redo logs alone
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You need a full DB backup and archived redo log files that
begin after the date of the backup
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STRUCTURE OF REDO LOG FILES
Redo log files store info as a result of DB activity
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Contents of redo log buffer are written by LGWR
process, to online redo log file, when:
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A transaction issues a COMMIT command
Redo log buffer is one-third full
Every 3 seconds
A checkpoint occurs
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Information is recorded in the redo log buffer in SGA
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The redo log file contains sets of redo records
A redo record (or redo entry) is made up of a related
group of change vectors that record a description of the
changes to a single block in the DB
 A single transaction may generate many redo entries
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REDO LOG MANAGEMENT
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ORACLE DATABASE STRUCTURE
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OVERVIEW OF ORACLE INSTANCE
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When a database is started, Oracle starts many
background processes and acquires memory
structures.
The combination of the background processes and
memory buffers is called an Oracle instance.
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ORACLE PROCESSES
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Read Chapter 9 Oracle Database Concept
A process is a connection or thread to the operating
system.
 Oracle processes – server processes and background
processes.
The background processes are the core of the Oracle
instance. When you start an instance, these processes are
created; when you shutdown an instance, these processes
are terminated.
Database writer
Log writer
Process monitor
System monitor
User processes – connecting users to the database
instance
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ORACLE PROCESSES
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Database Writer (DBW0): Database writer process uses a leastrecently-used (LRU) algorithm to identify dirty buffers and write
them to disk. Dirty buffers are buffers that contain data that has
been modified
Log Writer (LGWR): The log writer process is responsible for
writing the redo entries from the redo log buffer to the disk files.
Check Point (CKPT): The check point process performs check
point on an on-going basis. Check point flushes all the buffers
from the buffer cache to the disk and also all the current redo log
sequence number and time stamps are written to the all of the
data files.
Process Monitor (PMON): The process monitor monitors all
server processes. When ever a user connection fails, PMON is
responsible foe cleaning up the buffer cache and freeing up
system resources used by the failed process.
System Monitor (SMON): The system monitor is involved in
instance recovery when the database is started.
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ORACLE MEMORY STRUCTURES
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Read Chapter 8 Oracle Database Concept
The memory structures enable Oracle to share
executable code, and produces high performance.
Oracle uses two basic memory structures: shared
and process-specific
 System global area (SGA) – total memory shared
by all server processes including background
processes
 Program global area (PGA) – memory used for
private (application, program) processes
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SYSTEM GLOBAL AREA
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The SGA main components.
 Database buffer cache – recently used blocks of
data
 Shared pool – library cache, data dictionary cache
 Redo log buffer – a log of database changes
 Other Memory areas:
Large pool – optional large memory segments for shared SQL
and better performance
Java pool – memory for java code and data within the JVM
Streams pool – memory for using Streams
Automatic shared memory management: total
amount of SGA memory for the database
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DATABASE BUFFER CACHE
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Used to hold data blocks read from datafiles by
server processes
 Contains ‘dirty’ or modified blocks and ‘clean’ or
unused or unchanged bocks
 ‘Dirty’ and ‘clean’ blocks are managed in lists
called the dirty list and the LRU
 Free space is created by DBWR writing out ‘dirty’
blocks or aging out blocks from the LRU
 Size is managed by the parameter
DB_BLOCK_BUFFERS
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REDO LOG BUFFER
A circular buffer that contains redo entries
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Redo entries reflect changes made to the database
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Redo entries take up contiguous, sequential space
in the buffer
 Data stored in the redo log buffer is periodically
written to the online redo log files
 Size is managed by the parameter LOG_BUFFER
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Default is 4 times the maximum data block size for the
operating system
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SHARED POOL
Consists of multiple smaller memory areas
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Library cache
Shared SQL area
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Contains parsed SQL and execution plans for statements already
run against the database
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Procedure and package storage
Dictionary cache
Names of all tables and views in the database
 Names and datatypes of columns in the database tables
 Privileges of all users
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Managed via an LRU algorithm
 Size determined by the parameter
SHARED_POOL_SIZE
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PROGRAM GLOBAL AREA
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Program Global Area (PGA)
 Effectively used in session connection memory
 Broken into private chunks for each server
process
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It is a non shared memory created by Oracle
when a server process is started. Access to it is
exclusive to that server process and is read and
written only by Oracle code acting on behalf of
it. The total PGA memory allocated by each
server process attached to an Oracle instance is
also referred to as the aggregated PGA memory
allocated by the instance.
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SGA & BACKGROUND
PROCESSES
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BACKGROUND PROCESSES
(CONTINUED)
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DATABASE
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Oracle defines a DB as the collection of operating
system files that store your data
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Install the software components, create DB files to
store your data, and start a set of background
processes that allocate memory and handle
database activities
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Database server: combination of DB software, a
DB (the files), and DB instance (the SGA and the
background processes)
Single-instance server (typical configuration)
 Multiple-instance server
 Clustered servers
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SINGLE INSTANCE SERVER
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MULTI INSTANCE SERVER
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CLUSTERED SERVER
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ORACLE SOFTWARE OPTIONS
Enterprise Edition: includes all major components
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Standard Edition: provides basic support for
multi-user database applications on a smaller
scale than that of the Enterprise Edition
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Enables multiple users to connect concurrently
 Optimized for high data volume is common
 Supports multiple DB instances and replication
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Cannot be upgraded with database features
Personal Edition: single-user access to DB
instance
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Two primary uses: programming and deployment
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ORACLE SOFTWARE SOME ADDITONAL
OPTIONS
Optional features requiring additional license fees:
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Oracle Partitioning
Oracle Cluster ware
Oracle Spatial
Oracle Data Mining
Oracle Database Extensions for .NET
Oracle Advanced Security
And Other..
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Note: Some of the slides are from Oracle 10g Database
Administrator: Implementation and Administration by
Gavin Powell and Carol McCullough-Dieter
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