oracle database administration

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Oracle Database Administration

Session 2

System Level

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The Database

A database can be viewed as the collection of data from a business

An application presents this data to the users in a manageable way.

The application can insert, delete or update the data. The database structures hold and manipulate this

data

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The Database

The Data is stored in Relational Tables, defined by Columns

Data is stored as Rows in the table These tables can then be related to each other using

relationships The database enforces these relationships

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The Instance

A database instance (server) is a set of memory structures and background processes

The memory structures together makeup the System Global Area( SGA)

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The Instance This set of memory structures and background

processes are used to provide access to the data There can be multiple instances,or sets of memory

structures,for one database eg. Oracle Real Application Clusters (RAC)

A parameter file, the init.ora, is used to configure the instance

The parameters held in this file, determine the size and composition of the instance

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This file is read during the instance startup When some changes are made to the init.ora, they

will not take effect until the next time the database is started.

Pfile – Parameter File The parameter file is used to set the name of the

instance This is the SID (system identification) name Spfile – Server Parameter File

The Instance

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Database Structures

Three Types – Internal to the Database– Memory Based (SGA and Processes)– External to the Database

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Internal Database Structures

Tables– Tables are the storage mechanism for data inside

the oracle database. There are made up of columns. – Each column has a datatype and a length

Indexes– It is a partial copy of the data in a table– They are used to quickly find data in the database– An index is created when a primary key is created.

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Views– A method of looking at “some” of the data in a

table or in groups of tables– Views are masks over a table or group of tables– Views have no indexes – They can be used to enforce security

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Procedures– Blocks of PL/SQL statements, called by

applications– They do not return a value to the calling program

Functions– Like a procedure, but can return a value to the

calling program.


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Packages– These hold procedures and functions in logical

groups– A package can have PUBLIC and PRIVATE

elements– Public elements would be for a USERS usage– Private may be called by other procedures in the

package


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Triggers– Procedures that execute when a specific event

occurs– Used to augment referential integrity, enforce

additional integrity– Statement triggers– Row triggers


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Sequences– Sequential lists of unique numbers– Used as primary Keys

Synonyms– Synonyms are pointers to tables, views, procedures

functions.– To fully qualify an object we need the machine hostname,

the instance name, the objects owner and the object’s name

– Synonyms help to simplify the interface for the user


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Users– Users are not physical structures in database.– All objects are owned by a user– All users are associated to a specific default

tablespace– Users can be ‘granted’ access to the objects of

other users and ‘granted’ the privilege to execute a specific function or procedure

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Internal Database Structures Schemas

– They are related to users.– A set of tables and other database objects are

created as a schema and are owned by a user

Database Links– Database Links are used to reference data

outside the database– Database links can be public or private

Rollback Segments (Undo Segments)

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Memory Structures

– System Global Area (SGA) Part of the System Memory

– Unix level processes

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PMON SMON

DBW0 LGWR

Library CacheDictionary

Cache

ARCH

DatafilesRedo Log Files Archived Redo

Log Files

Data BlockBuffers Redo Log BuffersShared Pool

1

23 4

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System Global Area (SGA)

The Data Buffer Cache is the cache area where data blocks are read into from the data segments, such as tables, indexes, etc.

Its size is controlled by the db_cache_size parameter in the init.ora file.

This space is managed by a least recently used (LRU) algorithm

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System Global Area

The Data Buffer Cache is very important in database tuning

If data is not in this area, it must be read from the datafile, so we have disk I/O.

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System Global Area

The Shared Pool stores the data dictionary cache and the library cache

Data Dictionary Cache stores data from the data dictionary tables

These tables store information about the database objects

It is managed by a Least Recently Used (LRU) algorithm

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System Global Area

The Library Cache holds information about statements that have run against the database

It allows the sharing of commonly used SQL statements

It is also managed by an LRU algorithm Their sizes are set by the shared_pool_size

parameter

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System Global Area

Automatic SGA sizing

Automatic PGA Sizing

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System Global Area

The Redo log buffer holds redo data on a transaction, before it gets written to the redo log

Its size(in bytes) is controlled by the log_buffer parameter

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PMON SMON

DBW0 LGWR

Library CacheDictionary

Cache

ARCH

DatafilesRedo Log Files Archived Redo

Log Files

Data BlockBuffers Redo Log BuffersShared Pool

1

23 4

SGA

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Process Architecture

A process is a mechanism in an operating system that can run a series of steps.

A process has its own private memory area An Oracle database server has

– User processes – Oracle processes

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Background Processes

PMON cleans up failed user processes. It wake up periodically to check if it is needed.

SMON checks to see if a database needs recovery, on startup. It also coalesces free space in tablespaces.

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DBWR manages the data block buffer cache and the dictionary cache. It handles the batch writes of changed blocks from the SGA to the datafiles. There can be multiple DBWR processes.


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LGWR manages the writing of the contents of the redo log buffer, to the online redo log files. It writes the log entries in batches. If the redo logs are mirrored sets, then both are written to simultaneously. There can be multiple LGWR processes

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ARCH performs the archiving of the redo log files. LGWR writes to the redo log files in a round robin fashion. When all are full, it over-writes the first one. However, if the database is in archive mode, Oracle takes a copy of this file and stores it on disk.

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Oracle InstanceMemory structures

DatabaseDatafiles, Control files, etc

PMON SMON DBW0 LGWR

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The Physical World

The computer system– The operating system– Memory Modules– Storage Disks– Processors– Daemons

printers Networks

– Files

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System

Information on a computer is stored in bytes Bytes are grouped into Blocks The Operating System usually has 512 bytes in a

block 1K = 1024 bytes Oracle data is also stored in bytes Oracle data blocks are in 2k,4k,8k,16, or 32k bytes

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System

Oracle data blocks are multiples of the Operating System blocks

The computer memory uses the same block sizes as the disk storage

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System

The O/S software is Solaris 9 or 10 It is the layer between the computer hardware

and the Oracle Software It manages the computer system

– writes to disk– reads from disk– controls printing– controls network connections

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The OFA Standard

/oracle($O racle_base)

/app

/u01

/(other applications)

/app

/u02

/($S ID)

/oradata

/u03

/($S ID)

/oradata

/u04 /u05

/

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Oracle Directory Structure

bdum p udum p pfile cdum p arch create

<SID_NAM E>

adm in

netw ork dbs bin

$ORACLE_HOME

product

/u01/app/oracle ($ORACLE_BASE)

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Files

Datafiles contain the actual data stored in a database The Parameter file contain the initialization

parameters used to create the memory area used to manage the database

Control files map the physical files of the database to the logical tablespaces and online redo logs. It helps ensure the database remains consistent

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Files Redo files contain enough information to allow Oracle

to reconstruct or back out a transaction, if the database should shutdown before these changes have been written to the disk

INSERT, UPDATE, DELETE, CREATE, ALTER, or DROP operations generate redo information

Alert and Trace files contain information on the health of the database and provides warnings when problems occur

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Files

Backup files contain copies of the database files and can be used to recover the database.

The standard convention for file extensions or endings to file names are

– data files .dbf– control files .ctl– redo log files .dbf (some use .rdo)– parameter file .ora

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Datafiles and Tablespaces

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Oracle’s “Logical” World

A tablespace can belong to only one database

There must be at least two tablespaces, SYSTEM and SYSAUX to create a database

Other include USERS, UNDO, TOOLS, etc.

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Undo segments

Undo segments hold the before image of the data in a transaction

As a program begins to change the data in the database, Oracle changes the physical blocks that contain that information.

Before changing the data block buffers in the SGA or writing to disk, Oracle takes a copy of this data in an undo segment

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Tablespace Examples

– System holds all objects owned by the sys user– SYSAUX is an auxiliary tablespace to the SYSTEM

tablespace– Rollback (RBS) (undo) is used to store the

rollback segments– Temp (Temporary) is used for sort functions.

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Tablespace Examples

– Users is the default space for user accounts– Tools should be the default space for the system

user, after database creation.– Data holds the ‘real’ application data– Index holds the index data for the application

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Reading

10g and 11g Concepts Guide– Part 2

Chapter 3 Tablespaces,datafiles and control files

Chapter 5 Schema ObjectsChapter 7 The Data Dictionary

The two installation guides– A quick review of each. Look them over to

identify an overall process

oracle database administration

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