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MODULE 1DBMS STRATEGY AND ORACLE ARCHITECTURE

Database Administration Techniques and Practices

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ORGANIZATION’S DBMS STRATEGY

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

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 Scalability and availability, high performance Large database, concurrent users,

multiprocessors Examples: Oracle, DB2, SQL Server

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

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) Database (different) Instances (different) Schemas (common) Segments (Oracle specific)

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ORACLE DATABASE AND INSTANCE

An Oracle Database server consists of an Oracle Database and one or more Oracle Database instances.

Database: all Oracle related files Data files – holding tables and indexes System files – System, Undo, Temp Physical and logical structures

Instance: the combination of processes and memory Processes – background Memory – allocated to Oracle Running components – Instance is up

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ORACLE DATABASE AND INSTANCE

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PHYSICAL DATABASE STRUCTURE

Main types of files – data files, control files, redo log files, archived redo log files.

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

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

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 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: Checkpoints Changes

Data Manipulation Language (DML) Data Definition Language (DDL)

Datafile changes 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 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 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 Information is recorded in the redo log buffer in SGA

Contents of redo log buffer are written by LGWR process, to online redo log file, when: A transaction issues a COMMIT command Redo log buffer is one-third full Every 3 seconds A checkpoint occurs

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 MANAGEMENTFa

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ORACLE DATABASE STRUCTURE

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OVERVIEW OF ORACLE INSTANCE

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

Read Chapter 9 Oracle Database ConceptA 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

Database Writer (DBW0): Database writer process uses a least-recently-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

Read Chapter 8 Oracle Database ConceptThe 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

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

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 Redo entries reflect changes made to the database

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 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 Library cache

Shared SQL area Contains parsed SQL and execution plans for statements

already run against the database 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

Managed via an LRU algorithm Size determined by the parameter

SHARED_POOL_SIZE

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PROGRAM GLOBAL AREA

Program Global Area (PGA)Effectively used in session connection memoryBroken into private chunks for each server process

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 PROCESSESFa

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BACKGROUND PROCESSES (CONTINUED)

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DATABASE

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 Oracle defines a DB as the collection of

operating system files that store your data 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 SERVERFa

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MULTI INSTANCE SERVERFa

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CLUSTERED SERVERFa

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ORACLE SOFTWARE OPTIONS

Enterprise Edition: includes all major components Enables multiple users to connect concurrently Optimized for high data volume is common Supports multiple DB instances and replication

Standard Edition: provides basic support for multi-user database applications on a smaller scale than that of the Enterprise Edition Cannot be upgraded with database features

Personal Edition: single-user access to DB instance Two primary uses: programming and deployment

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ORACLE SOFTWARE SOME ADDITONAL OPTIONS

Optional features requiring additional license fees: Oracle Partitioning Oracle Cluster ware Oracle Spatial Oracle Data Mining Oracle Database Extensions for .NET Oracle Advanced Security And Other..

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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