Oracle dba-concise-handbook

Oracle DBA Concise Handbook
Oracle DBA Concise
Handbook
Covers 9i to 11g
Saikat Basak
Published by Ensel Software
www.enselsoftware.com
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© Saikat Basak
The author and publisher of this book have used their best efforts in preparing
this book. These efforts include the development, research and testing of the
theories and programs to determine their effectiveness. The author and
publisher shall not be liable in any event for the incidental or consequential
damages in connection with, or arising out of, the furnishing, performance, or
use of these programs.
All rights reserved. No part of this book may be reproduced, in any form or by
any means, without the permission in writing from the author.
1st
Edition 2004
2nd
Edition 2009 – updated for 10g & 11g
Last updated Jul 2010
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Contents
INTRODUCTION.............................................................................................6
1 ORACLE SERVER – AN OVERVIEW........................................................7
1.1 LOGICAL STRUCTURE........................................................................................7
1.2 ORACLE MEMORY STRUCTURE............................................................................7
1.3 BACKGROUND PROCESSES..................................................................................9
1.4 INSTALLING AND MANAGING ORACLE DATABASE.................................................12
1.5 ORACLE MANAGED FILES (OMF)..................................................................12
1.6 CREATING A NEW DATABASE...........................................................................12
1.7 STARTING UP DATABASE INSTANCE...................................................................15
1.8 SHUTTING DOWN DATABASE INSTANCE..............................................................15
1.9 CONTROL FILE...............................................................................................15
1.10 REDO LOG FILES.........................................................................................17
1.11 TABLE SPACES...........................................................................................20
1.12 SEGMENT AND STORAGE STRUCTURES.............................................................23
1.13 TABLES....................................................................................................24
1.14 INDEXES...................................................................................................25
1.15 CONSTRAINTS...........................................................................................27
1.16 USERS AND SECURITY.................................................................................29
2 BACKUP AND RECOVERY.......................................................................32
2.1 INTRODUCTION..............................................................................................32
2.2 BACKUP AND RECOVERY IN NO ARCHIVE LOG MODE.............................................32
2.3 BACKUP IN ARCHIVE LOG MODE.......................................................................32
2.4 USER MANAGED COMPLETE RECOVERY..............................................................33
2.5 USER MANAGED INCOMPLETE RECOVERY............................................................34
2.6 LOGICAL BACKUP – EXPORT/IMPORT AND DATA PUMP........................................34
2.7 SQL LOADER..............................................................................................36
2.8 NETWORKING FUNDAMENTALS.........................................................................37
2.9 LOG MINER..................................................................................................39
2.10 REAL APPLICATION CLUSTERS (RAC).........................................................42
2.11 STANDBY DATABASE (ALSO ORACLE DATA GUARD)........................................44
2.12 REPLICATION.............................................................................................44
3 PERFORMANCE TUNING.........................................................................45
3.1 TUNING DEVELOPMENT AND PRODUCTION SYSTEMS..............................................45
3.2 SOURCES OF TUNING INFORMATION...................................................................45
3.3 COLLECTING STATISTICS.................................................................................46
3.4 ORACLE SUPPLIED GUI TUNING TOOLS.............................................................47
3.5 SQL APPLICATION TUNING AND DESIGN............................................................47
3.6 OPTIMIZER...................................................................................................49
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3.7 TUNING SHARED POOL....................................................................................52
3.8 TUNING DATABASE BUFFER CACHE....................................................................54
3.9 SHARED SERVER............................................................................................56
3.10 LARGE POOL AND JAVA POOL.......................................................................57
3.11 TUNING REDO............................................................................................57
3.12 TUNING ARCHIVING OPERATIONS...................................................................58
3.13 TUNING DISK I/O.......................................................................................58
3.14 TUNING SORTS...........................................................................................58
3.15 TUNING ROLLBACK SEGMENTS......................................................................59
3.16 LOCKS......................................................................................................59
3.17 TUNING OPERATING SYSTEM.........................................................................60
3.18 AUTOMATIC WORKLOAD REPOSITORY (AWR)..............................................60
3.19 AUTOMATIC DATABASE DIAGNOSTIC MONITOR (ADDM) AND SQL TUNING
ADVISOR............................................................................................................60
4 SQL AND PL/SQL.........................................................................................62
4.1 COMPILING PACKAGES....................................................................................62
4.2 RECORDS AND TABLES ..................................................................................62
4.3 CURSOR.......................................................................................................62
4.4 MERGE, MULTI – TABLE INSERT AND PIVOT INSERT.............................................63
4.5 SQL JOINS..................................................................................................64
4.6 USEFUL SQL FUNCTIONS...............................................................................65
4.7 DYNAMIC PL/SQL.......................................................................................66
4.8 NESTED TABLE..............................................................................................67
4.9 TYPES OF JOINS.............................................................................................68
4.10 EXTERNAL TABLES......................................................................................70
5 DBMS PACKAGES.......................................................................................71
5.1 DBMS_JOB..............................................................................................71
5.2 UTL_FILE................................................................................................71
6 USEFUL SCRIPTS FOR DBAS...................................................................73
6.1 TO SHOW PRIMARY/FOREIGN KEY RELATIONSHIPS OF ALL TABLES AND VIEWS IN A
GIVEN SCHEMA....................................................................................................73
6.2 TO SEE ALL OBJECTS IN A TABLE SPACE FILE......................................................73
6.3 WHICH USER EXECUTING WHAT TYPE OF COMMAND.............................................74
6.4 GET OUTPUT OF A QUERY TO A TEXT FILE FROM SQL PLUS.................................74
6.5 TO SEE SIZE OF YOUR TABLES AND INDEXES.......................................................74
6.6 TO SEE FREE SPACES IN TABLE SPACES..............................................................74
7 NEW FEATURES OF 10/11G......................................................................76
7.1 WHAT IS G IN ORACLE'S GRID COMPUTING?.......................................................79
7.2 WHAT ARE ORACLE FUSION MIDDLEWARE (OFM) AND SERVICE ORIENTED
ARCHITECTURE (SOA)?......................................................................................80
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8 DBA INTERVIEW QUESTIONS................................................................83
8.1 OPEN-ENDED QUESTIONS.................................................................................83
8.2 TECHNICAL QUESTIONS...................................................................................83
8.3 QUESTIONS YOU SHOULD ASK..........................................................................90
9 REFERENCES...............................................................................................91
10 ORACLE SERVER’S DIAGRAMMATIC OVERVIEW.......................92
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Introduction
There are several books available in the market for Oracle DBAs. So what is
special about this book?
Well, the differences are several. First of all, this book is available in electronic
format. You can carry this book wherever you want. It is written in simple
Word format (PDF format is also available). So, you can open it in almost
anywhere. This book is based on the commands necessary for regular DBA
activities. This is a concise book. It attempts to be your first reference for DBA
job. You will still require looking at Oracle manuals and other huge references
for advanced commands and features. Please note that this book does not try to
teach you how to be a DBA. It is assumed that you know a bit of DBA
activities. It only acts as a DBA handbook.
I included a section on common DBA interview questions. Where do you find
such information in other books? Some avid readers wanted the answers to be
given along with. However, some questions are too easy. Some difficult
answers/hints have been provided. But I don’t appreciate providing all answers
because unless you have sound understanding of the concept, you can be very
easy bogged down by some twists in the questions.
This is really a CONCISE handbook. That’s why I couldn’t cover every nuts
and bolts of Oracle. Had I do so, this book would have consisted of more than
1000 pages and its charm would have been lost! Only the most basic aspects
have been touched. So, please don’t yell that why such and such topics have
been left. However, if readers strongly feel that some topics need to be added, I
shall definitely honor that demand.
I shall occasionally update the book. So, please visit the website frequently to
download latest version of the book.
Please note that originally I wrote this book for Oracle 9i and then updated for
11g.
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1 Oracle Server – an overview
1.1 Logical structure
Physical storage structures
Oracle database consists of 3 types of physical files –
• Data files – contains all database data
• Redo log files – record all changes made to data. Used for recovery
• Control files – maintains information about physical structure of database
1.2 Oracle memory structure
1.2.1 SGA
System Global Area (SGA) is shared memory area. All users of database share
information maintained in this area. The SGA and other background processes
constitute an Oracle instance.
SGA size is limited by SGA_MAX_SIZE initialization parameter.
From 11g, Oracle can manage SGA and PGA completely automatically.
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SYSTEM
Table
space
Table
space 1
Table
space 2
Database
Segment 1
Segment 2
Tablespace Segment
Extent 1
Extent 1
Blocks

Shared memory
From 11g, there are two new components in SGA viz Streams pool and Result
cache.
Non-shared memory
PGA
The database buffer cache is the area of memory that caches database data,
holding blocks from data files that have been read recently. Before a user can
look at a piece of information in an Oracle database, it must first reside in the
database buffer cache. Data gets into this cache based upon the Most Recently
Used algorithm. Because the most recently and most frequently used data is
kept in memory, less disk I/O is necessary, and overall database performance is
improved.
There are 3 types of buffers – dirty, free and pinned.
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SGA
Database buffer cache
Keep Recycle Default
Redo log buffer cache
Large pool (optional)
Java pool (optional)
Shared pool
Data
dictionary
cache
Control
structures
Library cache
Shared SQL
PL/SQL
procedures
& packages
Locks and
other
structures
Stack space Session info Sort area

Oracle uses an LRU mechanism to remove data from DB cache.
DB_CACHE_SIZE, DB_KEEP_CACHE_SIZE,
DB_RECYCLE_CACHE_SIZE determines DB cache size.
DB_CACHE_ADVICE can be set to ON/OFF/READY and the result can be
viewed from V$DB_CACHE_ADVICE.
Redo log buffer is a circular buffer in SGA that holds information about
changes made to data.
LOG_BUFFER determines its size.
1.2.2 Shared pool
Library cache contains shared SQL area, PL/SQL procedures and packages etc.
It is used for maintaining recently executed SQL commands and their execution
plans.
Data dictionary cache is a collection of database tables and views containing
metadata about the database, its structures, its privilege and its users. Oracle
accesses data dictionary frequently during parsing of SQL statements. Data
dictionary cache holds most recently used data dictionary information.
SHARED_POOL_SIZE determines size of shared pool and can be dynamically
altered.
PGA contains data and information for single server process.
PGA_AGGREGATE_TARGET specifies total amount of memory that can be
used by all server processes.
1.3 Background processes
1.3.1 Database Writer (DBWn)
Oracle marks buffers in memory as dirty when the data they contain is changed.
DBWn writes content of dirty buffer to data file when – a server process can’t
find a clean buffer after searching set threshold of buffers, a checkpoint occurs,
change table space to read only/offline/backup mode, drop/truncate table etc.
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1.3.2 Log Writer (LGWR)
It is responsible to redo log buffer management. Almost all activities against the
database are tracked in the online redo logs. As transaction are initiated and
eventually committed or rolled back, a record of this activity is written to these
log files.
Log writer writes to redo logs sequentially.
1.3.3 Checkpoint (CKPT)
Helps to reduce time required for instance recovery. A checkpoint is an event
that flushes modified data from buffer cache to disk and updates control file and
data files. The CKPT process updates header of data files and control files and
DBWn writes actual blocks to file. Checkpoint occurs automatically when an
online redo log file fills (log switch).
1.3.4 System Monitor (SMON)
At startup, SMON’s job is to ensure that all the database files are consistent and
perform recovery if required. There is also an assortment of other cleanup
activities that may need to be done, which are SMON’s responsibility. The
SMON process by itself checks every so often to see whether there are any tasks
waiting for its attention.
1.3.5 Process Monitor (PMON)
Cleans up failed user processes and frees all resources used by failed process.
1.3.6 Archiver (ARCn)
It automatically saves copies of redo logs in a DBA specified storage location
when media recovery is enabled.
1.3.7 Recover (RECO)
Is used with distributed transaction to resolve failure.
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1.3.8 Lock (LCKn)
It is used in RAC.
1.3.9 Dispatcher (Dnnn) & Shared Server (Snnn)
These are discussed later.
1.3.10 Manageability monitor (MMON)
From 10g, it makes snapshots of the database’s health (statistics) and stores this
information in the automatic workload repository.
1.3.11 Processing SQL
The following steps show how Oracle processes SQL
1. Statement is passed to Oracle for processing
2. Before it is placed in the library cache, a hash value is computed that
represent s a number of characteristics of the SQL.
3. Oracle compares the computed hash value against those values in a hash
table where it maintains for SQL statements already in the cache.
4. If a match is found, the new SQL statement is thrown away and the one
sitting in the cache is executed on its behalf.
5. In no match is found, further processing is done on the new SQL
statement, an entry is made in the library cache hash table for newly
arrived code, and it is placed in the library cache.
6. There are 3 stages of SQL processing – parse, execute and fetch
• During parsing, Oracle server checks the syntax and validates
table, column names against data dictionary
• Determines whether user has privilege to execute the statement
• Determines optimal execution plans for statement
• Finds a shared SQL area for the statement
• In execution stage, for UPDATE and DELETE statement, Oracle
locks the affected rows, looks for data blocks in DB buffer cache,
if found, executes becomes faster, if not then Oracle has to read
from physical data files to buffer cache. For SELECT and INSERT
statements, locking is not necessary.
• During fetch operation, rows are fetched to user process.
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1.4 Installing and managing Oracle database
To use operating system authentication, set
REMOTE_LOGIN_PASSWORDFILE parameter to NONE (default).
OS authenticated users can connect as CONNECT / AS SYSDBA (or
SYSOPER).
When using password file authentication, users connect to database by
specifying username and password.
1. Using ORAPWD utility, create a password file with SYS password.
2. Set REMOTE_LOGIN_PASSWORDFILE parameter.
3. Grant appropriate users SYSDBA or SYSOPER privilege.
1.5 Oracle Managed Files (OMF)
Set following parameters in initialization file.
DB_CREATE_FILE_DEST – default location of new datafiles
DB_CREATE_ONLINE_LOG_DEST_n – specifies location for online log files
and control files (max. 5 locations)
To create database using OMF, use
CREATE DATABASE MYDB DEFAULT TEMPORARY TABLESPACE
TMP;
1.6 Creating a new database
Usually when you install Oracle, it automatically creates a database for you
(though you need to specify a database name for this). Otherwise, you usually
use graphical Database Configuration Assistant (DBCA) to create/manage
databases. So, you may not even require creating a database from command
prompt. However, in case you need to, the steps are shown below.
In OS command prompt, use
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An Oracle instance consists of memory structures (SGA) and
background processes (DBWn, LGWR, CKPT, SMON, PMON,
MMON and optionally ARCn, Dnnn, Snnn etc.)

ORADIM -NEW -SID sid_name -INTPWD sys_password -MAXUSERS 10
In Windows, go to Control Panel – Services
Check service named OracleServiceSID started.
In My Computer, Environment tab, define
ORACLE_SID=sid_name
Create folders where you want to keep database files eg.
F:MYDBDATAFILES, UDUMP, BDUMP, CDUMP, LOGS, ARCHIVE etc.
Create a new initSID.ora file with relevant parameters
BACKGROUND_DUMP_DEST=F:MYDBBDUMP
CORE_DUMP_DEST=F:MYDBCDUMP
USER_DUMP_DEST=F:MYDBUDUMP
DB_NAME= sid_name
INSTANCE_NAME= sid_name
UNDO_MANAGEMENT=AUTO
UNDO_TABLESPACE=UNDO01
Start SQL Plus
/ AS SYSDBA
STARTUP NOMOUNT
CREATE DATABASE MYDB
MAXDATAFILES 30
MAXLOGFILES 10
MAXLOGMEMBERS 5
MAXINSTANCES 1
MAXLOGHISTORY 1
DATAFILE 'F:MYDBDATAFILESSYSTEM01.DBF' SIZE 100M
LOGFILE
GROUP 1 'F:MYDBLOGLOG01.DBF' SIZE 10M,
GROUP 2 'F:MYDBLOGLOG02.DBF' SIZE 10M
UNDO TABLESPACE UNDO01
DATAFILE 'F:MYDBUNDOUNDO01.DBF' SIZE 50M
DEFAULT TEMPORARY TABLESPACE TEMP
TEMPFILE 'F:MYDBTEMPTEMP01.DBF' SIZE 10M
CHARACTER SET WE8MSWIN1252
/
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CREATE SPFILE FROM PFILE;
Note: Above command was for Oracle 9i. From 10g, you need Sysaux table
space as well.
Now run calalog.sql (creates data dictionary views) and catproc.sql (creates PL/
SQL packages) from $ORACLE_HOMERDBMSADMIN
After installing Oracle, several services are registered in the server computer. In
Windows, (for Oracle 9.2) following services must be started as a minimum to
run Oracle – OracleOraHome92Agent, OracleOraHome92TNSListener and
OracleServiceSID (where SID is the name of database you created).
In Windows Vista running Oracle 11g, I usually start/stop my test database via
following batch file (say StartOracle.bat – MYDB is name of my database)
net start OracleServiceMYDB
net start OracleOraDb11g_home1TNSListener
net start OracleVssWriterMYDB
net start OracleDBConsoleMYDB
To stop database services, you can create a similar batch file by replacing start
with stop. In Vista, you need to run these batch files as administrator.
If you do not start OracleDBConsole<SID> service, then you won’t be able to
start web based Enterprise Manager – which you usually start from
https://localhost:1158/em (where localhost may be substituted for your
computer name)
You usually log on to Oracle server from “SQL Plus” as –
SYS/PASSWORD@DATABASENAME AS SYSDBA. Sometimes you can
also log in as simply “/ AS SYSDBA” only when you are physically in the same
computer where Oracle server is installed. Please note that Server Manager tool
is no longer available from Oracle 9i onwards. You can do everything using
SQL Plus!
For various day-to-day database works, you may find SQL Plus cumbersome to
work with. For this, several 3rd
party GUI tools are available. Two most popular
tools are – PL/SQL Developers and TOAD. From 11g, Windows SQL Plus has
been replaced by SQL Developer suite bundled with 11g. DOS version of SQL
Plus is still available though!
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1.7 Starting up database instance
SQL> STARTUP NOMOUNT
This state is used for creating new database or creating new control file. At this
state, Oracle allocates SGA and starts background processes.
SQL> STARTUP MOUNT
This state is used for performing specific maintenance operations like renaming
data files, enabling/disabling archive log mode, adding/dropping/renaming redo
log files, recovering database etc. Control file is read at this stage but the data
files are not open.
SQL> STARTUP OPEN or simply SQL>STARTUP
Database is available for normal operations.
NB: Oracle 11g requires at least 1 GB of RAM and 5 GB disk space to install.
For an operational production database, more RAM and disk space are required.
1.8 Shutting down database instance
SQL> SHUTDOWN NORMAL or simply SQL> SHUTDOWN
Waits for all database users to disconnect then closes database.
SQL> SHUTDOWN IMMEDIATE
Terminates all user connections, rolls back uncommitted transactions, closes
database.
SQL> SHUTDOWN TRANSACTIONAL
Waits for all transactions to commit or roll back, then closes database.
SQL> SHUTDOWN ABORT
Immediately closes database leaving it in inconsistent state. SMON
automatically performs instance recovery during next startup.
1.9 Control file
Control file contains –
• Database name
• Database creation timestamp
• Data files – name, location, on/off line status
• Redo log files – name, location
• Redo log archive information
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• Table space names
• Current log sequence number
• Most recent checkpoint information
• Begin and end of undo segments
• RMAN backup information
Oracle backs up control file after any structural changes in database. LGWR
updates control file with current log sequence number. CKPT updates control
file with recent checkpoint information. ARCn updates with archiving
information.
1.9.1 Multiplexing control files
Using init.ora
CONTROL_FILES =
(‘/ora/oradata/mydb/control1.ctl’, ‘/ora/oradata/mydb/control1.ctl’)
Using spfile
1. SQL> ALTER SYSTEM SET CONTROL_FILES = (‘/ora/oradata/mydb/
control1.ctl’, ‘/ora/oradata/mydb/control1.ctl’) SCOPE=SPFILE
2. SQL>SHUTDOWN NORMAL
3. Copy control file to new location
4. SQL>STARTUP
To create OMF control files, don’t specify CONTROL_FILES parameter in
initialization file; rather specify DB_CREATE_ONLINE_LOG_DEST_n
parameter n times starting with 1.
1.9.2 Creating new control file
Make sure you have complete list of all data and log files.
In SQL Plus, write (the database should be in STARTUP NOMOUNT)
CREATE CONTROLFILE SET DATABASE “MYDB”
NORESTLOGS NOARCHIVELOG
MAXDATAFILES 30
MAXLOGFILES 10
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MAXLOGMEMBERS 5
MAXINSTANCES 1
MAXLOGHISTORY 1
DATAFILE
'F:MYDBDATAFILESSYSTEM01.DBF'
'F:MYDBDATAFILESUSERS01.DBF'
'F:MYDBDATAFILESUNDO01.DBF'
'F:MYDBDATAFILESTEMP01.DBF'
LOGFILE
GROUP 1 'F:MYDBLOGLOG01.DBF' SIZE 10M,
GROUP 2 'F:MYDBLOGLOG02.DBF' SIZE 10M
/
To back up control file when database is running, use
ALTER DATABASE BACKUP CONTROLFILE TO filename REUSE
Or
ALTER DATABASE BACKUP CONTROLFILE TO TRACE – it places a text
copy of control file to USER_DUMP_DEST directory.
If Oracle can’t update control file, instance crashes.
1.9.3 Control file related data dictionary views
V$CONTROLFILE
V$CONTROLFILE_RECORD_SECTION
1.10 Redo log files
Redo entries record data changes that can be used to reconstruct all changes
made to database. Whenever you do any change to database (DML or DDL), it
is recorded in redo logs.
To operate successfully, an Oracle instance requires at least 2 redo log groups.
Each group must have at least 1 redo log file.
Usually in production databases, there are at least 3 redo log groups and each
group has at least 2 redo log members. Note that, all member files under same
group are identical. Members are multiple copies to protect against data loss in
case of disk failure.
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If LGWR can write to at least 1 member of the group, database functions
normally, but otherwise Oracle shuts down the instance.
1.10.1 Creating new groups and members
ALTER DATABASE ADD LOGFILE GROUP 3
(‘/oracle/oradata/log/redo31.log’, ‘/oracle/oradata/log/redo32.log’) SIZE 10M
ALTER DATABASE ADD LOGFILE MEMBER
‘/oracle/oradata/log/redo31.log’ TO GROUP 3
For OMF
ALTER DATABASE ADD LOGFILE
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1
2
3
Redo log files
3 groups and
3 members
each
Group 1 Group 2 Group 3

1.10.2 Renaming log members
Follow these steps
• Shutdown database
• Copy/rename redo log file member to new location
• SQL> STARTUP MOUNT
• ALTER DATABASE RENAME FILE old redo log file TO new redo log
file
• ALTER DATABASE OPEN
• Backup control file
1.10.3 Dropping redo log file
First, make the log file inactive, if necessary, issue ALTER SYSTEM SWITCH
LOGFILE
ALTER DATABASE DROP LOGFILE GROUP 3
ALTER DATABASE DROP LOGFILE MEMBER
‘/oracle/oradata/log/redo31.log’
1.10.4 Running database in archive log mode
Specify LOG_ARCHIVE_DEST_n parameters in initialization file.
E.g. LOG_ARCHIVE_DEST_1 = ((LOCATION = ‘/oradata/mydb/archive1’)
MANDATORY REOPEN = 60)
In 11g, to enable database archive log mode, define archive location like this
ALTER SYSTEM SET LOG_ARCHIVE_DEST_1='LOCATION=C:Oracle11goradataMYDBarchivelog'
SCOPE=SPFILE; (in mount state)
LOG_ARCHIVE_FORMAT = ‘arch_%t_%s’
%s – log sequence number
%S – log sequence number, zero filled
%t – thread number
%T – thread number, zero filled
To enable/disable archive log mode, follow these steps
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• Shutdown database (log in via conn / as sysdba)
• Startup and mount database
• SQL> ALTER DATABASE ARCHIVELOG (use NOARCHIVELOG to
disable)
• SQL> ALTER DATABASE OPEN
Till 9i, in the initialization file, set LOG_ARCHIVE_START = TRUE (if it is
not set, once a redo log file is full, Oracle hangs until redo log file is archived).
From 10g, this parameter is deprecated.
To manually initiate automatic archiving, issue ALTER SYSTEM ARCHIVE
LOG START and ALTER SYSTEM SWITCH LOGFILE commands.
To see whether database is in archive log mode, use
SQL> ARCHIVE LOG LIST
1.10.5 Redo log related data dictionary views
V$LOG – shows redo log status
V$LOGFILE – shows redo log files’ location
V$THREAD
V$LOG_HISTORY
V$ARCHIVED_LOG
V$ARCHIVE_DEST
V$ARCHIVE_PROCESSES
1.11 Table spaces
The database’s data is stored logically in table spaces and physically in data
files corresponding to the table spaces. One table space can have multiple data
file but one data file must belong to only one table space. A single object (say a
table) may span multiple data files but must reside within a single table space.
1.11.1 Creating table space
CREATE TABLESPACE supermarket DATAFILE
'e:oracleoradatamdbsupermarket.dbf' SIZE 30M
EXTENT MANAGEMENT LOCAL AUTOALLOCATE SEGMENT SPACE
MANAGEMENT AUTO
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CREATE TABLESPACE supermarket DATAFILE
'e:oracleoradatamdbsupermarket.dbf' SIZE 30M
AUTOEXTEND ON NEXT 10M MAXSIZE UNLIMITED
1.11.2 Dropping table space
DROP TABLESPACE supermarket INCLUDING CONTENTS AND
DATAFILES
1.11.3 Renaming table space
From Oracle 10g onwards, you can rename a table space (except System and
Sysaux)
ALTER TABLESPACE old_name RENAME TO new_name
When you rename a table space, all corresponding data dictionary entries are
updated.
1.11.4 Availability of table space
ALTER TABLESPACE supermarket OFFLINE
NORMAL/TEMORARY/IMMEDIATE/FOR RECOVER
You can’t place System table space in offline mode.
To make a table space read only,
ALTER TABLESPACE supermarket READ ONLY
To change it to read write mode,
ALTER TABLESPACE supermarket READ WRITE
1.11.5 Adding space to table space
ALTER TABLESPACE supermarket_DATA ADD DATAFILE
'c:oracleoradatamydbsupermarket_data2.dbf' SIZE 30M
ALTER DATABASE DATAFILE
'c:oracleoradatamydbsupermarket_data2.dbf' RESIZE 300M
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1.11.6 Table space related data dictionary views
DBA_TABLESPACES – all table space information
V$_TABLESPACE
DBA_FREE_SPACE
V$SORT_USAGE
DBA_SEGMENTS
DBA_USERS – shows default and temporary table space for users
1.11.7 Renaming and relocating file
Follow these steps to rename data file (for single table space except System
table space)
• ALTER TABLESPACE supermarket OFFLINE
• Copy or move the file to new location with OS commands
• ALTER DATABASE RENAME FILE
'c:oracleoradatamydbsupermarket_data2.dbf' TO
'c:oracleoradatamydbsupermarket_new.dbf'
or
ALTER TABLESPACE supermarket RENAME DATAFILE
• ALTER TABLESPACE supermarket ONLINE
In case of System table space or table spaces with multiple data files
• Shutdown database
• Copy or move the file to new location with OS commands
• Startup database in mount state
• ALTER DATABASE RENAME FILE
• Open database
Please note in case of Windows, the file may get locked unless database is
shutdown.
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1.11.8 Data file related data dictionary views
V$DATAFILE
V$TEMPFILE
DBA_DATA_FILES
DBA_TEMP_FILES
1.12 Segment and storage structures
PCTFREE = specifies what percentage of block should be allocated as free
space for future updates (default 10)
PCTUSED = specifies when the block can be considered for adding new rows
(default 40)
PCTFREE + PCTUSED <= 100
Blocks are smallest logical unit of storage in Oracle database.
An extent is logical storage unit made of contiguous data blocks.
Segment is logical storage unit made up of one or more extents.
Types of segments are – table, table partition, cluster, nested table, index, index
organized table, index partition, temporary, LOB, undo, bootstrap.
1.12.1 Undo segment
When a user performs an update or deletes operation, the earlier data is saved to
undo segments and then actual data is modified to new value. In case of insert
operation, rowid of new rows are stored in undo segments.
Undo data is not deleted immediately after commit or rollback. How long it will
stay in undo segment depends on UNDO_RETENTION parameter in
initialization file.
When a transaction is rolled back, Oracle restores the earlier data from undo
segments.
From Oracle 9i, undo management can be automatically controlled.
To use automatic undo management, set following parameters in initialization
file.
UNDO_MANAGEMENT=AUTO
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UNDO_TABLESPACE=table space name
1.12.2 Creating undo segment
CREATE UNDO TABLESPACE undo DATAFILE
‘/oradata/mydb/undo01.dbf’ SIZE 20M
To specify different table space as undo table space dynamically – issue
ALTER SYSTEM SET UNDO_TABLESPACE=undo02
1.12.3 Extent or segment related data dictionary views
DBA_EXTENTS
DBA_FREE_SPACE
DBA_SEGMENTS
V$SORT_SEGMENT
DBA_ROLLBACK_SEGS
V$ROLLNAME
V$ROLLSTAT
V$UNDOSTAT
1.13 Tables
1.13.1 Creating tables
Create table MANUFACTURER
(
MFDNO NUMBER not null,
MFDNAME VARCHAR2(200) not null,
ADDRESS VARCHAR2(200),
CITY VARCHAR2(50),
STATE CHAR(2),
COUNTRY VARCHAR2(100),
POSTCODE VARCHAR2(10),
PHONE VARCHAR2(50),
EMAIL VARCHAR2(100),
USERNAME VARCHAR2(20) default USER,
DATESTAMP DATE default SYSDATE
) tablespace SUPERMARKET_DATA
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CREATE TABLE MANUFACTURER
NOLOGGING PARALLEL
AS
SELECT * FROM COMPANY
1.13.2 Reorganizing tables
To move a table to a different table space
ALTER TABLE product MOVE TABLESPACE supermarket
1.13.3 Dropping a table
DROP TABLE schema.table_name (CASCADE CONSTRAINTS)
TRUNCATE TABLE table_name
Truncate resets HWM where delete does not.
Truncate is not logged but delete is logged.
1.13.4 Modifying columns
ALTER TABLE schema.table_name DROP COLUMN column_name
(CASCADE CONSTRAINTS)
ALTER TABLE schema.table_name SET UNUSED COLUMN
column1_name, column2_name (CASCADE CONSTRAINTS)
ALTER TABLE product ADD Mfd VARCHAR2(30) DEFAULT ‘abc’
1.13.5 Table related data dictionary views
DBA_TABLES
DBA_TAB_COLUMNS – all columns of all tables
1.14 Indexes
Oracle has mainly 2 types of indexes, B+ Tree and Bitmap.
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1.14.1 Creating index
Normal B tree index
CREATE INDEX index_name ON table_name (column_names)
TABLESPACE app_indx
Bitmap index
CREATE BITMAP INDEX emp_gender_idx ON employee (sex)
TABLESPACE app_indx
Reverse key index
CREATE INDEX index_name ON table_name (column_names)
REVERSE
Function based index
CREATE INDEX index_name ON UPPER(product (prodname))
To use function based index, set following parameters in initialization file
QUERY_REWRITE_ENABLED=TRUE
QUERY_REWRITE_INTEGRITY=TRUSTED
Cost based optimizer must be used.
1.14.2 Index Oraganized Table (IOT)
Create the table normally, with ORGANIZATION INDEX keyword. It is
suitable when data access is mostly thru primary key. In IOT, rows are
physically stored in sorted order of the primary key.
Create table MANUFACTURER
(
MFDNO NUMBER not null,
MFDNAME VARCHAR2(200) not null,
ADDRESS VARCHAR2(200),
CITY VARCHAR2(50),
STATE CHAR(2),
COUNTRY VARCHAR2(100),
POSTCODE VARCHAR2(10),
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PHONE VARCHAR2(50),
EMAIL VARCHAR2(100),
USERNAME VARCHAR2(20) default USER,
DATESTAMP DATE default SYSDATE
) tablespace SUPERMARKET_DATA
ORAGANIZATION INDEX
OVERFLOW TABLESPACE ovfl_tblsp
INCLUDING address
PCTTHRESHOLD 25
MAPPING TABLE
1.14.3 Rebuilding index
ALTER INDEX pk_customer REBUILD ONLINE
DROP INDEX pk_customer
You can also move index to a different table space using ALTER INDEX
index_name TABLESPACE new_table_space command.
1.14.4 Monitoring index usage
ALTER INDEX index MONITORING USAGE
The V$OBJECT_USAGE view populated with index usage information.
ALTER INDEX index NOMONITORING USAGE
1.14.5 Index related data dictionary views
DBA_INDEXES
DBA_IND_COLUMNS
1.15 Constraints
Types of constraints – not null, check, unique, primary key, foreign key
ALTER TABLE table MODIFY column NOT NULL
ALTER TABLE table MODIFY column NULL
ALTER/CREATE TABLE table (….)
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CONSTRAINT ck_bonus check ( bonus > 0 )
ALTER TABLE table ADD CONSTRAINT ck_bonus check ( bonus > 0 )
CREATE TABLE product (….)
CONSTRAINT pk_prodcode PRIMARY KEY (prodcode)
ALTER TABLE product ADD CONSTRAINT pk_prodcode PRIMARY KEY
(prodcode)
ALTER TABLE product ADD CONSTRAINT fk_mfd FOREIGN KEY
(mfdby) REFERENCES manufacturer(mfdno) ON DELETE CASCADE
Constraints created are enabled by default. You can create it as disabled by
using DISABLED keyword at end of command.
ALTER TABLE table DROP CONSTRAINT constraint
ALTER TABLE table DROP PRIMARY KEY CASCADE
1.15.1 Enabling/disabling constraints
ALTER TABLE table DISABLE CONSTRAINT constraint
ALTER TABLE table ENABLE CONSTRAINT constraint
ALTER TABLE table MODIFY CONSTRAINT constraint ENABLE
ALTER TABLE table MODIFY CONSTRAINT constraint DISABLE
1.15.2 Validated constraints
Enable validate – default, existing rows and future rows are checked
Enable novalidate – existing rows not checked but future rows are checked
Disable validate – existing rows checked but future rows are not checked (no
DML is allowed on table)
Disable novalidate – no check done on existing or future rows
ALTER TABLE table MODIFY CONSTRAINT constraint ENABLE
NOVALIDATE
1.15.3 Deferring constraints
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If constraint is created with DEFERABLE clause, you can define whether
constraint checking will be done immediately (INITIALLY IMMEDIATE,
default) or later (INITIALLY DEFEREED).
ALTER TABLE name MODIFY CONSTRAINT cons_name INITALLY
DEFFERED (or IMMEDIATE)
1.15.4 Index related data dictionary views
DBA_CONSTRAINTS
DBA_CONS_COLUMNS
1.16 Users and security
1.16.1 Profile
Profiles are used to control database resource usage. DEFAULT profile is
created at creation time of database. To enforce resource limit,
RESOURCE_LIMIT=TRUE should be set in initialization file.
CREATE PROFILE OFFICE_USER LIMIT
SESSIONS_PER_USER 6
CONNECT_TIME 1440
IDLE_TIME 120
FAILED_LOGIN_ATTEMTS 3
PASSWORD_LOCK_TIME UNLIMITED
ALTER USER clerk PROFILE office_user
1.16.2 Users
CREATE USER MKM
IDENTIFIED BY MKM
DEFAULT TABLESPACE SUPERMARKET_DATA
TEMPORARY TABLESPACE TEMP
QUOTA UNLIMITED ON SUPERMARKET_DATA
PROFILE DEFAULT
GRANT CONNECT, RESOURCE, SELECT_CATALOG_ROLE,
EXECUTE_CATALOG_ROLE TO MKM
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DROP USER mkm CASCADE
1.16.3 Privilege
Privileges control what users can or can’t do in database.
Object privilege – provides permission to access schema objects. Granted for
specific objects.
GRANT SELECT, UPDATE ON product, price TO clerk (WITH GRANT
OPTION)
System privilege – provide right to perform structural change in database level.
GRANT CREATE ANY TABLE TO john (WITH ADMIN OPTION)
REVOKE CREATE ANY TABLE FROM john
For object privileges, both grantor and grantee information is stored in data
dictionary; where as for system privilege, only grantee information is stored.
1.16.4 Roles
A role is named set of privileges.
CREATE ROLE CLERK
GRANT SELECT, INSERT, UPDATE ON TRANSACTION TO CLERK
ALTER USER john DEFAULT ROLE CLERK (NONE)
1.16.5 User related data dictionary views
DBA_USERS
DBA_TS_QUOTA – space assigned to users
V$SESSION – users currently connected to database
DBA_TAB_PRIVS
DBA_COL_PRIVS
DBA_SYS_PRIVS
SESSION_PRIVS
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DBA_ROLES
DBA_ROLES_PRIVS
ROLE_ROLE_PRIVS
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2 Backup and Recovery
2.1 Introduction
When instances crashes for any reason (e.g. Power failure) Oracle automatically
recovers when database starts next time.
The most important decision you need to take for backup is to decide whether
the database will run in archive or no archive log mode. Usually production
databases always run in archive log mode.
Ideally, each member of archive log groups should reside in different physical
disks so that if one disk gets corrupt, identical copies can be retrieved from
another disk.
Backup can be either user managed (copying files with OS commands) or server
managed (RMAN – Recovery Manager based). If you use RMAN, you can have
incremental backups (i.e. backing up only changed blocks since last backup).
RMAN is not discussed in this book.
2.2 Backup and recovery in no archive log mode
When the database is running in no archive log mode, only cold back up can be
taken. The steps are –
1. Shutdown the database
2. Copy data files, control files, redo log files using OS commands to a
backup location.
3. Startup database
If any of the files (data/control/redo) is corrupt in no archive log mode, you
need to restore all files from backup. If relocation of files is necessary, you need
to open the database in mount stage and issue rename command to specify new
location of the files. Then you should open database for normal use. In no
archive log mode, you can only recover data, which was taken during back up
period. Even if only one file is corrupt, you need to restore all files and recover
entire database.
2.3 Backup in archive log mode
In archive log mode, backup can be taken while database is running.
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To take backup of data file, follow these steps –
1. ALTER TABLESPACE name BEGIN BACKUP
2. Use OS commands to copy data file
3. ALTER TABLESPACE name END BACKUP
Data file headers don’t get updated until backup ends. Ideally, perform hot
backup when there is less DML is occurring in the database.
2.4 User managed complete recovery
In all the following cases, it is assumed that database is running in archive log
mode and backup was already taken.
2.4.1 System table space lost/corrupt
1. STARTUP MOUNT
2. Restore only system table space file
3. If required, relocate file – ALTER DATABASE RENAME file TO new
file
4. RECOVER AUTOMATIC DATABASE (or DATAFILE file name)
5. ALTER DATABASE OPEN
2.4.2 Non-system table space lost/corrupt
1. STARTUP MOUNT
2. Make data file offline – ALTER DATABASE file name OFFLINE
4. Restore data file from backup to database location
5. If required, relocate file – ALTER TABLESPACE table space name
OFFLINE IMMEDIATE for issuing check point
6. RECOVER AUTOMATIC TABLESPACE table space name
7. ALTER TABLESPACE table space name ONLINE
2.4.3 Non-system table space lost/corrupt when no backup taken
1. STARTUP MOUNT
2. ALTER DATABASE CREATE DATAFILE filename with path AS new
filename (only if relocate)
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3. RECOVER DATABASE (DATAFILE filename)
2.4.4 Instance failed during backup
Entire database won’t start. Data file header freezes during backup, so no
checkpoint information is written.
1. STARTUP MOUNT
2. ALTER DATABASE END BACKUP
2.5 User managed incomplete recovery
2.5.1 Time/Cancel/Change (SCN) based
1. STARTUP MOUNT
2. Restore all data files (including system, data, index, undo but not control
file or redo log files)
3. RECOVER DATABASE UNTIL TIME ‘dd-mon-yyyy hh24:mi:ss’ (or
CANCEL or CHANGE number)
4. ALTER DATABASE OPEN RESETLOGS
Log sequence number will be re-initialized.
SHUTDOWN
Take full backup of database
2.6 Logical backup – export/import and Data Pump
Export may be either through conventional path or direct path. In direct path
export, the evaluating buffer is bypassed and makes it faster.
Most common export command is (from OS command prompt) –
EXP ‘sys/password@mydb as sysdba’
Most common parameters are –
FILE – output file (default expdat.dmp)
DIRECT – direct path (N)
OWNER – list of owners/users
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TABLES – list of table names
PARFILE – parameter file name (in this file you can store all options)
TABLESPACES – list of table spaces to export
TRANSPORT_TABLESPACE – export transportable table space metadata (N)
Similarly, import is run as –
IMP ‘sys/password@mydb as sysdba’
FILE – input file (expdat.dmp)
IGNORE – ignore create object errors (N)
ROWS – import data rows (Y)
Example of export,
exp system/password file=F:Databaseexp_mkm.dmp owner=mkm rows=y
You can run export/import in interactive mode i.e. it will ask you about
parameters during runtime.
Data pump
From 10g onward, Oracle introduces new utilities EXPDP and IMPDP (as run
from OS command prompt) to fast data loading (export/import). As it uses API,
it is significantly faster than export/import utility. You can even monitor data
pump progress from data dictionary views.
Data pump is run as – IMPDP user/password DIRECTORY=data_pump_dir
DUMPFILE=dpdump.dmp JOB_NAME=my_import
Where, DIRECTORY is an external directory name already created. EXPDP
has similar syntax.
Oracle automatically creates data_pump_dir in $ORACLE_HOME/ admin/
database_name/ dpdump. However if you want you can create a directory of
your own like this –
create directory data_pump_dir as
'C:Oracle11gadminMYDBdpdump';
You can view location of directory by
select * from dba_directories where DIRECTORY_NAME = 'DATA_PUMP_DIR'
Example:
expdp system/password DIRECTORY=data_pump_dir
DUMPFILE=supermarket.dmp SCHEMAS=mkm
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Oracle now advises use of data pump over export/import.
2.7 SQL Loader
Using SQL Loader, you can load data from text file to Oracle tables.
The components you need to run SQL Loader are –
1. Control file – specifies how to load data in Oracle
2. Data file – the data in text file which will be loaded
3. Discard file – data that is discarded by SQL Loader because of not
matching load condition
4. Bad file – data that SQL Loader could not load because of error
5. Log file – synopsis of loading operation
If you specify DIRECT=Y option, SQL Loader will bypass buffer and save data
directly into data blocks in the disk. It makes data loading very fast however,
this option does not enforce constraints, does not fire insert triggers, does not
allow SQL functions in control file and locks entire table during loading.
You can run SQL Loader from OS command prompt as –
SQLLDR user/password@db CONTROL=myfile.ctl
A sample control file is shown below (assuming input data file is | delimited).
LOAD DATA
INFILE 'F:DUMPCUSTOMER.TXT'
BADFILE 'F:DUMPCUSTOMER.BAD'
DISCARDFILE 'F:DUMPCUSTOMER.DSC'
APPEND
INTO TABLE CUSTOMER
FIELDS TERMINATED BY "|"
TRAILING NULLCOLS
(
CUSTNO DECIMAL EXTERNAL "sq_cust_no.nextval",
CUSTNAME CHAR,
SEX CHAR,
ADDRESS CHAR,
CITY CHAR,
STATE CHAR,
COUNTRY CHAR,
POSTCODE CHAR,
PHONE CHAR,
EMAIL CHAR,
NOTE CHAR,
DATESTAMP DATE "YYYY-MM-DD HH24:MI:SS”
)
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Note for NUMBER columns you specify DECIMAL EXTERNAL and for
VARCHAR2 columns you specify CHAR in SQL Loader control file.
2.8 Networking fundamentals
Oracle Net is an internal layer which manages communication between client
and server. It is configured on server, client, web server etc.
2.8.1 Configuring Oracle Net on server
Listener is a server-side networking component, which listens for requests from
client on server. To communicate with Oracle server, Listener service must be
started on server. Listener is configured in server using listener.ora file.
Following is a sample listener.ora file.
# LISTENER.ORA Network Configuration File:
E:oracleora92networkadminlistener.ora
# Generated by Oracle configuration tools.
LISTENER =
(DESCRIPTION_LIST =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC0))
)
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = ensel)(PORT =
1521))
)
)
)
SID_LIST_LISTENER =
(SID_LIST =
(SID_DESC =
(GLOBAL_DBNAME = MDB)
(ORACLE_HOME = E:oracleora92)
(SID_NAME = MDB)
)
)
You can manage listener from OS command prompt using LSNRCTL utility.
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Oracle Net Manager is a tool using which you can manage most client/server
configuration files.
2.8.2 Configuring Oracle Net on client
Usually you connect to Oracle server from client as USER/PASSWORD@DB
(this is known as connect descriptor).
How the database name you specified in connection is resolved to exact
database in the server is known as name resolution method.
Most popular name resolution methods are – host naming, local naming (most
common using tnsnames.ora) and Oracle Internet Directory naming.
In tnsnames.ora file (usually in client machine it resides in $ORACLE_HOME /
network/admin folder). A sample tnsnames.ora file is shown below.
# TNSNAMES.ORA Network Configuration File:
E:oracleora92networkadmintnsnames.ora
# Generated by Oracle configuration tools.
MDB =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = ensel)(PORT = 1521))
)
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = MDB)
)
)
MARKET =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = 109.125.257.250)(PORT
= 1521))
)
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = MARKET)
)
)
Most common connection problem is “ORA-12154 TNS could not resolve
service name”. When this occurs, check the client is looking at correct
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tnsnames.ora file (there may be multiple version in computer). You can verify
this by checking TNS_ADMIN environment variable. Also check whether
client computer can talk to server computer by running “TNSPING server ip
address” command. Or you can use PING SID command as well.
Check sqlnet.ora file and see whether it specifies local naming first. This file
resides in both client and server.
Sample of what an sqlnet.ora file will contain.
NAMES.DIRECTORY_PATH= (TNSNAMES, ONAMES, HOSTNAME)
2.9 Log Miner
Using log miner, you can examine redo log files!
2.9.1 Running log miner
Specify a directory by UTL_FILE_DIR=E:ORACLEORADATAUNLOAD
parameter and bounce database.
Create a dictionary file
EXECUTE DBMS_LOGMNR_D.BUILD
('dictionary.ora','E:ORACLEORADATAUNLOAD', OPTIONS =>
DBMS_LOGMNR_D.STORE_IN_FLAT_FILE);
Add log files
exec dbms_logmnr.add_logfile ('E:oracleoradataMDBArchive1
ARC00026.001', dbms_logmnr.new);
ARC00027.001', dbms_logmnr.addfile);
Start log miner session
exec dbms_logmnr.start_logmnr (dictfilename=>
'E:ORACLEORADATAUNLOADdictionary.ora');
Once the redo logs were analyzed, all the DDL (and some DML) statements
applied in the source database will be found in the V$LOGMNR_CONTENTS
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view. Important columns of this view are - SQL_UNDO, SQL_REDO,
USERNAME, SCN, TIMESTAMP, COMMIT_TIMESTAMP, TABLESPACE,
SEG_NAME, SEG_TYPE, and OPERATION.
The Log Miner session is closed by executing following command in the same
session.
EXEC DBMS_LOGMNR.END_LOGMNR
After the session is complete, all data in the v$logmnr_contents table are
deleted. Be sure to execute CREATE TABLE my_logmnr AS SELECT ... to
copy the data before analyzing the contents.
2.9.2 Filtering data that is returned
Log Miner can potentially be dealing with large amounts of information. There
are several methods you can use to limit the information that is returned to the
V$LOGMNR_CONTENTS view, as well as the speed at which it is returned.
These options are specified when you start LogMiner.
Showing Only Committed Transactions
At the time of starting
EXECUTE DBMS_LOGMNR.START_LOGMNR(OPTIONS =>
DBMS_LOGMNR.COMMITTED_DATA_ONLY);
Filtering Data By Time
EXECUTE DBMS_LOGMNR.START_LOGMNR(DICTFILENAME =>
'/oracle/dictionary.ora', STARTTIME => TO_DATE('01-Jan-2004
08:30:00', 'DD-MON-YYYY HH:MI:SS'), ENDTIME => TO_DATE('01-
Jan-2004 08:45:00', 'DD-MON-YYYY HH:MI:SS'));
Filtering Data By SCN
EXECUTE DBMS_LOGMNR.START_LOGMNR(DICTFILENAME =>
'/oracle/dictionary.ora', STARTSCN => 100, ENDSCN => 150);
2.9.3 Querying on log miner
Some examples are shown below.
SELECT USERNAME, SQL_REDO FROM V$LOGMNR_CONTENTS
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WHERE USERNAME <> 'SYS';
SELECT OPERATION, SQL_REDO, SQL_UNDO FROM V$LOGMNR_CONTENTS
WHERE SEG_OWNER = 'MKM' AND SEG_NAME = 'PRODUCT' AND OPERATION
= 'INSERT' AND USERNAME = 'MKM';
2.9.4 Log miner related data dictionary views
V$LOGMNR_CONTENTS - Shows changes made to user and table
information.
V$LOGMNR_DICTIONARY - Shows information about the Log Miner
dictionary file, provided the dictionary was created using the
STORE_IN_FLAT_FILE option.
V$LOGMNR_LOGS - Shows information about specified redo logs. There is
one row for each redo log.
V$LOGMNR_PARAMETERS - Shows information about optional Log Miner
parameters, including starting and ending system change numbers (SCNs) and
starting and ending times.
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2.10 Real Application Clusters (RAC)
An RAC database is a clustered database. In RAC environment, multiple Oracle
instances (which are connected via interconnect) operate on same database files
on disk. Different servers must access set of shared disks and should
communicate through high-speed interconnection. Changed database blocks and
log information on one instance can be moved to another instance through
memory interconnection without writing on disk. This is known as cache fusion
(see later). The main advantage of RAC is scalability and high availability.
Several servers with Oracle instances can be added to system. If one of them
fails, others continue to work without affecting operations. For this reason RAC
is also known as High Availability. When work load grows, you can simply add
another server to the grid (RAC is a type of grid computing after all).
The data files are stored in several disk drives which are connected by cluster
aware storage. By adding multiple instances, we can add and remove and single
Oracle instance without bringing the database down. So, database always
remains available. That is the essence of RAC - high availability.
An RAC database is managed by Oracle Clusterware. RAC operates in shared
everything architecture mode.
Any storage (eg. SAN, SCSI etc.) can be used with RAC. However, good I/O
speed is required for scalability of data volume.
RAC supports up to 100 clusters which may be different at hardware level but
must run same operating system.
Oracle recommends using ASM (Automatic Storage Management) for ease of
dealing with clustered storage.
An Oracle RAC database requires three components - cluster nodes (the servers
or computers running Oracle instances), shared storage (disk drives) and Oracle
Clusterware (software application).
Installing RAC
The first step of working with RAC is to install "Oracle Clusterware" which is
installed via Universal Installer.
Then you have to configure the clusterware.
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Then install ASM (Automatic Storage Management).
Now install Oracle 11g database.
Then perform post installation tasks. This ensures that clusterware and database
are installed properly and they are aware of each other.
It is possible to convert your normal single instance Oracle database to an RAC
database. You can achieve this via Enterprise Manager or rconfig utility.
Administering Clusterware
Oracle Clusterware includes two important components: the voting disk and the
OCR. The voting disk is a file that manages information about node
membership, and the OCR is a file that manages cluster and Oracle RAC
database configuration information.
RAC can be administered via Oracle Enterprise manager. On EM's web console
mode, click on Availability tab to see details of Clusterware. You can click on
Topology tab to see a visual representation of your nodes. The Interconnect tab
shows you info on interfaces. You can also add new instance to clusterware via
EM (under Server tab).
Oracle Clusterware posts alert messages in alert log – which is under
$CRS_home. RAC data dictionary views are created by catclust.sql.
Cache Fusion
Oracle RAC uses Cache Fusion to synchronize the data stored in the buffer
cache of each database instance – i.e. to keep track of which nodes are writing
to which blocks and to ensure that two nodes do not update duplicate copies of
the same block. Since all computers/instances in an RAC access the same
database, the overall system must guarantee the coordination of data changes on
different computers such that whenever a computer queries data it receives the
current version – even if another computer recently modified that data. Oracle
RAC refers to this functionality as Cache Fusion. It involves the ability of RAC
to fuse in-memory data cached physically separately on each computer into a
single global cache. This saves a lot of resource time.
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2.11 Standby database (also Oracle Data Guard)
Stand by database is used as a protection against failure of main production
database.
2.11.1 Physical stand by
This may be created from last back up taken for the production database and
there after applying archived redo log files on it. This is similar to recovering a
database. However, for stand by database, this recovery is like a continuous
process, because, archived logs (from production database) are continuously
being applied on it to make it sync with production database. However, stand by
database won’t be available for use until recovery is completed.
2.11.2 Logical stand by
Instead of applying archived redo log files, SQL statement is constructed from
log files are being applied to stand by database (similar to Log Miner method).
The database is available for use during application of SQLs.
2.12 Replication
It allows you to have multiple copies of same database at different locations. At
most basic level, replication is implemented using materialized views. In case of
synchronous replication, transactions are either successfully propagated to all
sites or it is rolled back. It ensures no conflict will occur between sites. It
requires stable network environment and mostly used for read only materialized
views. In asynchronous replication, changes to each site is stored locally and
forwarded to other sites. In this case, conflict resolution processes are required.
Replication generally improves performance across network. For example, if
you use a database for online transactions as well as reporting, you can replicate
the database and run transactions and reporting on different versions.
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3 Performance Tuning
3.1 Tuning development and production systems
Oracle’s top down approach for development systems
1. Tune data design
2. Tune application design
3. Tune memory allocation
4. Tune I/O and physical structures
5. Tune resource contention
6. Tune for underlying platform (OS)
Oracle’s production performance tuning principles
1. Define problem clearly and formulate a tuning goal
2. Examine host system and gather statistics
3. Compare common problems with Oracle’s documentation
4. Get a conceptual picture of what went wrong from gathers statistics
5. Identify changes to be done and implement those changes
6. Check whether tuning objective has been met or not, repeat steps until
tuning is complete.
3.2 Sources of tuning information
3.2.1 Alert log file
This file records information and error messages for various database activities.
This file is located at BACKGROUND_DUMP_DEST folder. The name format
is alert_SID.log.
3.2.2 Trace files
Background process trace files contains session information for process that
created them. These files are available in BACKGROUND_DUMP_DEST
folder. Name format for the trace file is usually SID_PROCESS_nnnn.trc e.g.
mdb_lgwr_1598.trc.
User trace files are found in USER_DUMP_DEST folder. These are created
when error occurs in user’s server process. User tracing can be enabled using
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ALTER SESSION SET SQL_TRACE = TRUE command or by executing
package as
EXEC
SYS.DBMS_SYSTEM.SET_SQL_TRACT_IN_SESSION
(sid, serial#, TRUE)
3.2.3 Views commonly used in tuning
V$SGASTAT
V$EVENT_NAME
V$SYSTEM_EVENT
V$SESSION_EVENT
V$SESSION_WAIT
V$STATNAME
V$SYSSTAT
V$SESSTAT
V$SESSION
V$WAITSTAT
DBA_TABLES
DBA_INDEXES
DBA_STATS
DBA_DATA_FILES
DBA_SEGMENTS
DBA_HISTOGRAMS
3.3 Collecting statistics
Run UTLBSTAT and UTLESTAT to collect all database activities in the given
time period in a single file.
Run from $ORACLE_HOME/rdbms/admin/utlbstat.sql and utlestat.sql
The resulting file is named as REPORT.TXT
3.3.1 Statspack
• Run spcreate.sql script from $ORACLE_HOME/rdbms/admin folder.
• It will create PERFSTAT schema with all required objects.
• To collect statistics, use EXECUTE STATSPACK.SNAP procedure (as
PERFSTAT user). A snapshot of statistics will be collected and stored in
PERFSTAT schema tables.
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• Use $ORACLE_HOME/rdbms/admin/spauto.sql to run automatic
statistics collection at specific intervals.
• Once you gathered enough statistics, you can generate a report using
$ORACLE_HOME/rdbms/admin/spreport.sql script.
3.4 Oracle supplied GUI tuning tools
Capacity Planner
Performance Manager – observe database performance.
Top Sessions – see which users are consuming most resource
Trace Data Viewer
Lock Monitor
Top SQL – most resource consuming SQLs
Performance Overview – see current performance of database
Oracle Expert – gathers statistics and gives recommendations for tuning
Index Tuning Wizard – identify unused indexes
3.5 SQL application tuning and design
3.5.1 TKPROF
It is used to format user trace files. Usage example is (from OS command
prompt) – TKPROF ORA_1234.TRC TRACE.TXT
Some of its parameters are –
EXPLAIN – generates explain plan for each statement in trace file
SYS – output file includes recursive SQL statements (i.e. those involving data
dictionary queries)
RECORD – specifies a file where SQL statements of trace file are written
Example usage
TKPROF ORA_1234.TRC TRACE.TXT SYS=NO
EXPLAIN=MKM/MKM@MDB RECORD=SQL.TXT
To identify SQL statements, which may require tuning, look for statements –
• Consuming excess CPU resource
• Taking long time to parse, execute and fetch
• Reading too many data blocks from disk and too few from SGA
• Access many data blocks but return only few rows
3.5.2 Explain plan
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• Create plan table using $ORACLE_HOME/rdbms/admin/utlxplan.sql
• Populate PLAN_TABLE using EXPLAIN PLAN FOR… command. For
example,
EXPLAIN PLAN
SET STATEMENT_ID = 'PRICE'
FOR
SELECT P.PRODCODE, P.PRODNAME, J.SELLPRICE, M.MFDNAME,
NVL(SUM(I.QTYAVAILABLE),0) "ALL STORES QTY"
FROM PRODUCT P
JOIN PRICE J ON (P.PRODCODE = J.PRODCODE)
LEFT JOIN MANUFACTURER M ON (P.MFDBY = M.MFDNO)
LEFT JOIN INVENTORY I ON (P.PRODCODE = I.PRODCODE)
WHERE SYSDATE BETWEEN J.STARTDATE AND J.ENDDATE
AND P.HASSERIALNO=0
GROUP BY P.PRODCODE, P.PRODNAME, J.SELLPRICE, M.MFDNAME
• To view the plan, you may issue following statement
SELECT LPAD(' ',4*(LEVEL-2)) || OPERATION || ' ' ||
OPTIONS || ' ' ||
OBJECT_NAME "EXECUTION_PLAN", IO_COST,
CPU_COST,TEMP_SPACE
FROM PLAN_TABLE
START WITH ID = 0 CONNECT BY PRIOR ID = PARENT_ID
• Remember that, if you run the above query, you will see the plan in an
indented view. The innermost operations are executed first. If two
operations appear at same level (with same inner level), the top one is
executed first.
3.5.3 Auto trace
Unlike explain plan, auto trace executes the actual SQL statement before
generating the plan.
You need to create PLUSTRACE role by running plustrce.sql as SYS user.
Then you need to assign PLUSTRACE role to users who will use auto trace.
They also need PLAN_TABLE in their schemas.
To use auto trace, issue following command from SQL Plus.
SET AUTOTRACE ON
Then issue any SQL statement and you will always see statistics after result is
displayed.
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3.6 Optimizer
Earlier versions of Oracle used Rule Base Optimizer (RBO). But latest versions
use Cost Based Optimizer (CBO) by default.
Statistics must be gathered to benefit from CBO.
3.6.1 Gathering statistics
ALTER INDEX index_name COMPUTE STATISTICS
ALTER TABLE table_name COMPUTE STATISTICS
ALTER TABLE table_name ESTIMATE STATISTICS FOR
TABLES/COLUMNS col1, col2/ALL COLUMNS/ALL INDEXES
EXECUTE DBMS_UTILITY.ANALYZE_SCHEMA('MKM','COMPUTE')
Oracle now recommends that you use DBMS_STATS package instead of
Analyze.
EXEC DBMS_STATS.gather_schema_stats (ownname => ‘MKM’, cascade
=>true, estimate_percent => dbms_stats.auto_sample_size)
3.6.2 Optimizer modes
In initialization file, you can set optimizer mode as shown below
OPTIMIZER_MODE=CHOOSE (this is default) or FIRST_ROWS or
ALL_ROWS or RULE or FIRST_ROWS_n where n = 1/10/100/1000.
You can also change optimizer mode at session level.
ALTER SYSTEM SET OPTIMIZER_MODE=CHOOSE
To change optimizer mode at statement level, you should use hints using /*+ …
*/.
SELECT /*+ RULE */ …
Commonly used hints are – FULL, INDEX, REWRITE, and PARALLEL etc.
If statistics exists for any one table or index involved in SQL statement, CBO is
used, otherwise RBO is used.
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To reuse a saved execution plan, you can use “plan stability” (in the form of
stored outline) feature or “materialized view”.
3.6.3 Materialized view
Unlike in normal view, materialized view actually stores the data in tables.
To create materialized view, issue
CREATE MATERIALIZED VIEW schema.mview_name
BUILD IMMEDIATE
REFRESH ON DEMAND (or REFRESH COMPLETE ON COMMIT)
ENABLE QUERY REWRITE
AS
SELECT query;
EXEC DBMS_MVIEW.REFRESH('schema.mview_name','C');
EXEC DBMS_MVIEW.REFRESH_ALL_DEPENDENT('table_name');
EXEC DBMS_MVIEW.REFERSH_ALL_MVIEWS;
3.6.4 Partitioned tables
3.6.4.1 Range partition
It uses range of column values to determine where the record will be inserted.
CREATE TABLE student (…) PARTITION BY RANGE (graduation_year)
(PARTITION p_2000 VALUES LESS THAN 2000 TABLESPACE student_1,
PARTITION p_2002 VALUES LESS THAN 2002 TABLESPACE student_2,
PARTITION p_2004 VALUES LESS THAN 2004 TABLESPACE student_3,
PARTITION p_error VALUES LESS THAN (MAXVALUE) TABLESPACE
student_4);
3.6.4.2 List partition
It is based on set of specified value instead of range of values.
CREATE TABLE student (…) PARTITION BY LIST (degree)
(PARTITION p_engg VALUES (‘BTech’,’MTech’) TABLESPACE stu_engg,
PARTITION p_comm VALUES (‘Mcom’,’Bcom’) TABLESPACE stu_comm,
PARTITION p_arts VALUES (‘MA’,’BA’) TABLESPACE stu_arts);
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3.6.4.3 Hash partition
It uses a hashing algorithm to assign records in particular partition. It usually
keeps almost equal number of records in each partition.
CREATE TABLE student (…) PARTITION BY HASH (roll_no)
PARTITIONS 3 STORE IN (stu_1, stu_2, stu_3);
3.6.4.4 Composite partition
It uses range partition and inside it uses hash sub-partitions. Data is physically
stored in sub-partition level.
CREATE TABLE student (…)
PARTITION BY RANGE (graduation_year)
SUBPARTITION BY HASH (roll_no) SUBPARTITIONS 3
STORE IN (stu_1, stu_2, stu_3)
(PARTITION p_2000 VALUES LESS THAN 2000,
PARTITION p_2002 VALUES LESS THAN 2002,
PARTITION p_2004 VALUES LESS THAN 2004,
PARTITION p_error VALUES LESS THAN (MAXVALUE));
Note: Any bitmap indexes created on partitioned table must be local (to the
partition).
3.6.4.5 Cluster
A cluster is a group of one or more tables whose data is stored at same place
(physically). This helps faster access of data columns, which are often queried
as joins because Oracle server needs to read less number of physical data
blocks.
CREATE CLUSTER dept_emp
(dno NUMBER) SIZE 1000 TABLESPACE clst
CREATE INDEX dept_emp_idx
ON CLUSTER dept_emp TABLESPACE idx
CREATE TABLE dept (dno NUMBER, dname VARCHAR2(100))
CLUSTER dept_emp(dno);
CREATE TABLE emp (eno NUMBER, ename VARCHAR2(100), dno
NUMBER) CLUSTER dept_emp(dno);
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Oracle 11g allows reference partition and interval partition.
Take an example of Transaction and Transaction Detail tables. These two are
linked by foreign key TransId. Now, master table has transaction date but detail
table do not. We want both tables be partitioned by transaction date. In 11g, we
can specify details tables be partitioned based on foreign key reference TransId.
Interval partition is useful when we do not know how many partitions we need
beforehand. In above example, we can specify the table such a way whenever
new month begins, a new partition will be created automatically.
3.7 Tuning shared pool
Shared pool consists of library cache and data dictionary cache. Library cache
caches most recently used SQL and PL/SQL statements. Data dictionary cache
caches data dictionary information. Shared pool is managed by a Least Recently
Used algorithm.
Finding a matching SQL statement in shared pool is known as cache hit. For
cache hit to occur, two SQL statements must be exactly same i.e. their ASCII
value equivalent should be same. The aim of tuning shared pool is to maximize
cache hit ratio.
3.7.1 Measuring shared pool performance
High cache hit ratio indicates that your application users are getting results of
SQL and PL/SQL mostly from memory rather than reading from disk.
SELECT * FROM V$LIBRARYCACHE
The value in GETHITRATIO column for SQL AREA, TABLE/PROCEDURE,
BODY and TRIGGER rows should be very close to 1 i.e. 100%.
Similarly PINHITRATIO should also be very close to 1.
GET is referred to parse lock, while PIN is referred to execution time locks.
A well-tuned OLTP system should have GETHITRATIO and PINHITRATIO
90% or higher for SQL AREA.
Data dictionary performance is measured by
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SELECT 1-(SUM(GETMISSES)/SUM(GETS)) “Data dictionary hit
ratio” FROM V$ROWCACHE
This value should be over 0.85 for OLTP systems.
3.7.2 Improving shared pool performance
3.7.2.1 Add more memory to shared pool
The size of shared pool is determined by SHARED_POOL_SIZE initialization
parameter.
SELECT POOL, SUM(BYTES) "SIZE" FROM V$SGASTAT WHERE POOL =
'shared pool' GROUP BY POOL
Use following command to change shared pool size
ALTER SYSTEM SET SHARED_POOL_SIZE=200M
3.7.2.2 Make space for large PL/SQL statements
You can set aside a reserved area in SGA for large PL/SQL packages. This area
is controlled by SHARED_POOL_RESERVED_SIZE parameter.
Determine which packages are loaded into memory from following command
SELECT * FROM V$DB_OBJECT_CACHE WHERE TYPE IN ('PACKAGE',
'PACKAGE BODY')
3.7.2.3 Keep important PL/SQL code in memory
You can “pin” most frequently used PL/SQL code in memory. To do this –
1. Build DBMS_SHARED_POOL package by running
$ORACLE_HOME /rdbms/admin/dbmspool.sql script.
2. Load a package using EXECUTE
DBMS_SHARED_POOL.KEEP(‘PACKAGE_NAME’)
You can see which packages are pinned by issuing
SELECT OWNER, NAME, TYPE FROM V$DB_OBJECT_CACHE WHERE KEPT =
‘YES’
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You must have very good knowledge of application to determine which objects
to pin right after instance startup. You can audit PL/SQL packages, triggers,
sequences etc. and find out which objects are most frequently accessed.
3.7.2.4 Code reuse
Use bind variables like SELECT * FROM CUSTOMER WHERE CUST_ID
= :cust_id
Implement strict coding standard (i.e. capitalization, indentation etc.) so that
chances of finding identical statement in memory will increase.
3.7.2.5 Tune cache specific initialization parameters
OPEN_CURSORS (default 50, increase if necessary)
CURSOR_SPACE_FOR_TIME (set to FALSE for Forms based applications)
SESSION_CACHED_CURSORS
CURSOR_SHARING (use FORCE, SIMILAR or default EXACT)
3.8 Tuning database buffer cache
It caches most recently accessed data blocks into memory. If data is not found
from cache, it is fetched from disk. It is operated on LRU mechanism (except,
only for full table scan, it is placed on MRU end.)
Buffer may be free, pinned, clean or dirty.
DBWn writes dirty (changed) buffer to disk.
3.8.1 Measuring buffer cache hit ratio
SELECT 1-(physical.VALUE - direct.VALUE - lobs.VALUE) /
(logical.VALUE) "Buffer cache hit ratio"
FROM v$sysstat physical, v$sysstat direct, v$sysstat lobs,
v$sysstat logical
WHERE physical.NAME = 'physical reads'
AND direct.NAME = 'physical reads direct'
AND lobs.NAME = 'physical reads direct (lob)'
AND logical.NAME = 'session logical reads'
The ratio should be more than 0.90 for OLTP systems.
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3.8.2 Improving buffer cache hit ratio
3.8.2.1 Add more space
ALTER SYSTEM SET DB_CACHE_SIZE = 100M
Set DB_nK_CACHE_SIZE parameters in initialization file to access multi-
block database.
To get an idea how much you should increase buffer cache size
• Set DB_CACHE_ADVICE = ON initialization parameter.
• Query V$DB_CACHE_ADVICE view.
3.8.2.2 Use multiple buffer pools
Use keep, recycle and default pool by setting DB_KEEP_CACHE_SIZE,
DB_RECYCLE_CACHE_SIZE and DB_CACHE_SIZE (default) initialization
parameters.
Determining which segments to cache in keep and recycle pools, you must have
in depth knowledge of the application.
SELECT username "owner", NAME "seg name", kind "seg type",
COUNT(DISTINCT BLOCK#) "No. buffers"
FROM v$cache v, dba_users d
WHERE v.owner# = d.user_id
GROUP BY NAME, username, kind
HAVING COUNT(DISTINCT BLOCK#)>10
ORDER BY 3 DESC
Oracle recommends you consider caching of segments in keep pool whose total
size is less than 10% of default pool size.
To assign segments to pool, use
ALTER TABLE schema.package STORAGE (BUFFER_POOL KEEP);
ALTER TABLE schema.package STORAGE (BUFFER_POOL RECYCLE);
Monitor buffer pool statistics
SELECT NAME "Buffer pool",
1-(physical_reads/(db_block_gets+consistent_gets)) "Buffer
pool hit ratio"
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FROM v$buffer_pool_statistics
ORDER BY NAME
3.8.2.3 Cache tables in memory
CREATE TABLE (…) CACHE
ALTER TABLE name CACHE
3.8.2.4 Use proper indexes
Build indexes on foreign key columns of tables that reference a primary key
column in another table.
3.9 Shared server
By default, Oracle runs on dedicated server mode where for each user session
connection, a server process is created on server and a user process is created on
client machine. When number of concurrent users becomes very high, shared
server (known as Multi Threaded Server in earlier versions) is used.
In shared server, several (up to 5) dispatcher background processes are run in
server, which accept user requests. They then put the request in a queue.
Thereafter, shared server processes pick the request from queue and process the
SQL (i.e. parsing the statement, reading segments from disk and placing them in
buffer cache etc.). After processing, they put the result in response queue. The
corresponding dispatcher sends back the result to user process.
Shared server is useful for these scenarios – many application users, short
application transactions (e.g. railway reservation system, order entry system),
non-continuous transactions etc.
Shared server is a scalability improvement feature not performance
improvement feature. You will always have same or better performance by
using dedicated server feature.
3.9.1 Configuring shared servers
Set following parameters in initialization file
DISPATCHERS = n (0 to 5)
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SHARED_SERVERS = n (1 to OS dependent max. value)
Other optional parameters are – MAX_DISPATCHERS, CIRCUITS,
MAX_SHARED_SERVERS, and PROCESSES
3.9.2 Measuring shared server performance
Query on V$SHARED_SERVER_MONITOR view.
The following query shows shared server busy ratio
SELECT NAME, decode(busy+idle,0,0,round((busy/
(busy+idle))*100,4)) "busy rate" FROM v$shared_server WHERE
status != 'QUIT'
The next query shows dispatcher busy ratio
SELECT NAME "dispatcher", NETWORK, (round(SUM(busy)/
(SUM(busy)/SUM(idle)),4))*100 "busy rate"
FROM v$dispather GROUP BY NAME, NETWORK
Additional dispatcher is necessary is busy ratio found from above query is more
than 50%.
Please note that DBA must connect through dedicated server to perform various
DBA activities (e.g. startup/shutdown database).
3.10 Large pool and Java pool
Large pool in SGA is used for Recovery Manager (RMAN) operations and
parallel query.
It is defined by LARGE_POOL_SIZE (usual values from 600K to 2GB)
parameter in initialization file and cannot be changed dynamically.
Java pool is used to keep session specific Java application code and variables.
Its size is determined by JAVA_POOL_SIZE (default 20M) initialization
parameter and cannot be changed dynamically.
3.11Tuning Redo
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Its performance is measured by the amount of time server process waits to
access redo log files. The following queries can be used to measure redo log
waits.
SELECT r.VALUE/e.VALUE "Redo log buffer retry ratio"
FROM v$sysstat r, v$sysstat e
WHERE r.NAME = 'redo buffer allocation retries'
AND e.NAME = 'redo entries'
Its value should be less than 1%.
SELECT NAME,VALUE FROM v$sysstat WHERE NAME = 'redo log space
requests'
Constantly increase value indicates too small redo log files.
3.11.1 Improving redo log performance
Make it bigger. Redo log space is specified by LOG_BUFFER initialization
parameter.
Reduce redo log generation by using UNRECOVERABLE and NOLOGGING
keywords in SQL statements.
3.12 Tuning archiving operations
Common problems are –
• Archive location getting full – you can temporarily change archive log
location by ALTER SYSTEM ARCHIVE LOG ALL TO
‘/oradata/archive’.
• ARCn process can’t keep up with redo log generations – create more
ARCn process.
3.13 Tuning disk I/O
Keep separate table spaces for different functional segments.
Measure data file I/O from following views – V$FILESTAT, V$DATAFILE,
V$TEMPFILE.
3.14 Tuning sorts
Minimize sorting activity. If required, perform in memory whenever possible.
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Sort may be measured by following query
SELECT m.VALUE/(d.VALUE+m.VALUE) "In memory sort ratio"
FROM v$sysstat m, v$sysstat d
WHERE m.NAME = 'sorts (memory)' AND d.NAME = 'sorts (disk)'
This ratio should be more than 0.95
Increase value for SORT_AREA_SIZE initialization parameter if necessary.
Disk sort is performed in temporary table space file.
3.15 Tuning rollback segments
From Oracle 9i, automatic undo management does away manual rollback
segment management. However, you can set a specific rollback segment for
large transaction by this command –
• CREATE PRIVATE ROLLBACK SEGMENT rbs STORAGE (INITIAL
1M NEXT 10M) TABLESPACE rbstb
• ALTER ROLLBACK SEGMENT rbs ONLINE
• SET TRANSACTION USE ROLLBACK SEGMENT rbs
• EXEC procedure
• ALTER ROLLBACK SEGMENT rbs ONLINE
3.16 Locks
Lock contention occurs when multiple users try to obtain lock on specific object
at the same time. Lock is released only after COMMIT or ROLLBACK
statement.
See lock contention from following views.
V$LOCK
V$LOCKED_OBJECT
DBA_WAITERS
DBA_BLOCKERS
To resolve lock contention, avoid coding long transactions and don’t use
restrictive explicit locks. It is always better to let Oracle handle all locks.
You can kill any session using ALTER SYSTEM KILL SESSION ‘sid, serial#’
command.
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3.17 Tuning operating system
Try to avoid paging and swapping.
If server has multiple CPUs, use Oracle’s parallel query, parallel DML, parallel
ANALYZE and parallel index creation features. In multiple CPU machines,
Oracle will itself change many parameters.
You can allocate and manage server resources using Oracle’s Resource
Manager feature (not discussed here).
On Unix, all server processes and background processes are run as separate
executables (you can see them using ps command). However, on Windows, all
those processes run as threads inside ORACLEservicename.EXE process.
3.18 Automatic Workload Repository (AWR)
From 10g, AWR continuously captures database statistics and derives metrics
from it. This is of immense help during database tuning.
Among many others, AWR collects following statistics
• Wait events used to identify performance problems.
• Some system and session statistics from the V$SYSSTAT and
V$SESSTAT views.
• Object usage statistics.
• Resource intensive SQL statements
AWR information is used by ADDM and SQL Tuning Advisor (discussed
below)
AWR related package is DBMS_WORKLOAD_REPOSITORY. The
DBA_HIST% views contain historical data stored in the database.
3.19 Automatic Database Diagnostic Monitor (ADDM) and SQL Tuning
Advisor
From 10g, ADDM constantly monitors database and in case of any problem, it
will suggest what you should do next. The ADDM findings can be queried from
DBA_ADVISOR% objects on data dictionary. Note that ADDM analysis is
based on AWR snapshots, which have a default frequency of once an hour and a
default retention period of 8 days.
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An ADDM analysis is performed after each AWR snapshot (every hour by
default), and the results are saved in the database.
Remember, the goal of database performance tuning is to reduce the DB time of
the system for a given workload.
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4 SQL and PL/SQL
All source code of packages, procedures and functions are written in
DBA_SOURCE, ALL_SOURCE or USER_SOURCE views.
4.1 Compiling packages
ALTER PROCEDURE procedure COMPILE
ALTER PACKAGE package COMPILE
ALTER PACKAGE package COMPILE BODY
4.2 Records and Tables
PL/SQL records are similar to C structures.
DECLARE
TYPE tEmp IS RECORD (
ENO NUMBER, FNAME VARCHAR2(50), LNAME VARCHAR2(50));
vEmp tEmp;
BEGIN
SELECT id, fname, lname INTO vEmp FROM employee;
END;
You can use %ROWTYPE to specify a variable of table row type. For example,
vEmp employee%ROWTYPE;
PL/SQL Tables are similar to 1-dimensional array in C. You can visualize it as
a table with only 2 columns – KEY and VALUE.
DECLARE
TYPE tEmp IS TABLE OF VARCHAR2(50) INDEX BY BINARY_INTEGER;
vEmp tEmp;
BEGIN
vEmp(1) = 'Saikat';
END;
Some table attributes are – tablename.COUNT, DELETE, DELETE(i), FIRST,
LAST, NEXT(i), PRIOR(i).
4.3 Cursor
Declaring cursor
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CURSOR cursor_name IS SELECT statement;
Processing cursor
OPEN cursor_name;
FETCH cursor_name INTO variable(s);
CLOSE cursor_name;
Cursor attributes
%FOUND, %NOTFOUND, %ISOPEN, %ROWCOUNT
Cursor FOR loop
FOR variable IN cursor_name LOOP
Statement(s);
END LOOP;
4.4 Merge, multi – table insert and pivot insert
An example of merge command is shown below.
MERGE INTO MANUFACTURER M
USING NEW_MANUFACTURER WM
ON (M.MFDNO = WM.MFDNO)
WHEN MATCHED THEN UPDATE
SET M.MFDNAME = WM.MFDNAME, M.ADDRESS = WM.ADDRESS, M.CITY = WM.CITY,
M.STATE = WM.STATE, M.COUNTRY = WM.COUNTRY
WHEN NOT MATCHED THEN
INSERT (M.MFDNO, M.MFDNAME, M.ADDRESS, M.CITY, M.STATE, M.COUNTRY)
VALUES (WM.MFDNO, WM.MFDNAME, WM.ADDRESS, WM.CITY, WM.STATE, M.COUNTRY);
Similarly, an example of multi – table insert follows.
INSERT ALL
WHEN MEDIA = ‘BOOK’ THEN
INTO BOOK VALUES (NO, TITLE, PRICE)
WHEN MEDIA = ‘CD’ THEN
INTO SOFTWARE VALUES (NO, TITLE, PRICE)
WHEN MEDIA = ‘VCD’ THEN
INTO VIDEO VALUES (NO, TITLE, PRICE)
SELECT MEDIA, NO, TITLE, MEDIA FROM PRODUCT;
Using pivot insert, you can create multiple rows of data from single record. Say,
SALES_SOURCE_DATA comes from a non-relational source and it contains
following columns – emp_id, sales_mon, sales_tue, sales_wed, sales_thu and
sales_fri. We like to store this information in SALES_INFO table which has
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following fields – emp_id, week, sales. We can achieve it by using the
statement shown below.
INSERT INTO SALES_INFO VALUES (emp_id, week, sales_mon)
INSERT INTO SALES_INFO VALUES (emp_id, week, sales_tue)
INSERT INTO SALES_INFO VALUES (emp_id, week, sales_wed)
INSERT INTO SALES_INFO VALUES (emp_id, week, sales_thu)
INSERT INTO SALES_INFO VALUES (emp_id, week, sales_fri)
SELECT emp_id, sales_mon, sales_tue, sales_wed, sales_thu, sales_fri FROM
SALES_SOURCE_DATA.
Thus for 1 row in SALES_SOURCE_DATA, we shall have 5 rows in
SALES_INFO table. This feature is also known as normalization is some other
database applications.
4.5 SQL Joins
Oracle now follows ANSI/ISO join syntax (similar to SQL Server). You can
also use earlier versions join syntax. However, new ANSI/ISO standard syntax
is more comprehensive. Here are few examples.
Say we have 2 tables – EMP (eno, ename, dno) and DEPT (dno, dname). To list
all employee names and department names we can now write following query.
SELECT E.ENAME, D.DNAME FROM EMP JOIN DEPT ON (E.DNO = D.DNO)
We can use LEFT, RIGHT or FULL keywords for outer join. For example, to
list all employees even when some employees may not belong to any
department, we can issue this query.
SELECT E.ENAME, D.DNAME FROM EMP LEFT JOIN DEPT ON (E.DNO =
D.DNO)
This is definitely more intuitive than earlier syntax with “+” operator!
Example of updating columns of table with data from another table:
CREATE TABLE INFO1 (CODE VARCHAR2(3) PRIMARY KEY,
COUNTRY VARCHAR2(100), CAPITAL VARCHAR2(100), PHONECODE NUMBER(4),
CURRENCYCODE VARCHAR2(3));
INSERT INTO INFO1 VALUES ('IND','India','New Delhi',NULL,NULL);
INSERT INTO INFO1 VALUES ('GBR','United Kingdom','London',NULL,NULL);
INSERT INTO INFO1 VALUES ('FRA','France','Paris',NULL,NULL);
INSERT INTO INFO1 VALUES ('USA','United States','Washington DC',NULL,NULL);
INSERT INTO INFO1 VALUES ('ITA','Italy','Rome',NULL,NULL);
INSERT INTO INFO1 VALUES ('SWE','Sweden','Stockholm',46,'SEK');
COMMIT;
CREATE TABLE INFO2 (CODE VARCHAR2(3), PHONECODE NUMBER(4), CURRENCYCODE
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VARCHAR2(3) );
INSERT INTO INFO2 VALUES ('IND',91,'INR');
INSERT INTO INFO2 VALUES ('GBR',44,'GBP');
INSERT INTO INFO2 VALUES ('FRA',33,'EUR');
INSERT INTO INFO2 VALUES ('USA',1,'USD');
INSERT INTO INFO2 VALUES ('CAN',1,'CAD');
COMMIT;
/* case 1 – wrong */
UPDATE INFO1 i1 SET (PHONECODE,CURRENCYCODE) = ( SELECT PHONECODE,
CURRENCYCODE FROM INFO2 i2 WHERE i1.CODE = i2.CODE )
-- Sweden's data becomes null by running this!!
/* case 2 – correct */
UPDATE INFO1 i1 SET (PHONECODE,CURRENCYCODE) = ( SELECT PHONECODE,
CURRENCYCODE FROM INFO2 i2 WHERE i1.CODE = i2.CODE )
WHERE EXISTS ( SELECT 1 FROM INFO2 i22 WHERE i1.CODE = i22.CODE)
-- Sweden's existing data remains correct
4.6 Useful SQL functions
Decode – some examples have been provided in chapter “Useful scripts for
DBAs”.
Case – example
SELECT COUNTRY, CONTINENT
CASE CONTINENT WHEN 1 THEN ‘EUROPE’
WHEN 2 THEN ‘ASIA’
WHEN 3 THEN ‘AFRICA’
ELSE ‘OTHER’ END CONTINENT_NAME
FROM COUNTRIES
With clause example
WITH
x AS
(
select 'Tom' as FirstName FROM dual union
select 'Dick' FROM dual union
select 'Barney' FROM dual union
select 'Betty' FROM dual
),
z AS
(
select 'Flintstone' as LastName FROM dual union
select 'Rubble' FROM dual
)
SELECT * FROM x,z
NVL (x, y) returns y if x is null or x otherwise.
NVLS (x, y, z) returns z if x is null, y if x is not null.
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INSTR (string where to search, string what to search, start position default 1,
what “n-th” occurrence default 1st
) is used for searching for pattern inside a
string. Returns the number position where occurrence has been found or 0 if not
found.
SUBSTR (string, x, y) returns portion of string that is y characters long starting
from position x.
ROUND (15.2568, 2) produces 15.26.
Pivot and Un-pivot examples – can be used to transpose rows/columns.
/* PIVOT */
WITH fly_table AS (
SELECT 'John' "Customer",'Apple' "Item", 5 "Qty" FROM dual UNION
ALL
SELECT 'Jill','Orange', 2 FROM dual UNION ALL
SELECT 'Sally','Banana', 6 FROM dual UNION ALL
SELECT 'John','Orange', 2 FROM dual UNION ALL
SELECT 'Sally','Apple', 1 FROM dual UNION ALL
SELECT 'John','Orange', 1 FROM dual UNION ALL
SELECT 'Sally','Apple', 1 FROM dual
)
SELECT * FROM (
SELECT "Customer","Item", SUM("Qty") "Qty" FROM fly_table GROUP BY
"Customer", "Item"
) PIVOT ( SUM("Qty") FOR "Item" IN ('Apple','Banana','Orange'))
/* UNPIVOT */
WITH fly_table AS (
SELECT 'India' "Country",'New Delhi' "Capital" FROM dual UNION
SELECT 'UK','London' FROM dual UNION
SELECT 'USA', 'Washington DC' FROM dual UNION
SELECT 'Germany','Berlin' FROM dual
)
SELECT COL, VALUE FROM (
SELECT * FROM fly_table
)
UNPIVOT INCLUDE NULLS ( VALUE FOR COL IN ("Country","Capital"))
4.7 Dynamic PL/SQL
A sample is given below
CREATE TABLE TEST.EMP(NO NUMBER, NAME VARCHAR2(100));
CREATE OR REPLACE PROCEDURE DynSql
(pNo IN test.emp.no%TYPE,
pName IN test.emp.NAME%TYPE)
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AS
cur INTEGER;
p INTEGER;
stmt VARCHAR2(100);
BEGIN
cur := dbms_sql.open_cursor;
stmt := 'INSERT INTO TEST.EMP VALUES(:no,:name)';
dbms_sql.parse(cur,stmt,dbms_sql.v7);
dbms_sql.bind_variable(cur,':no',pNo);
dbms_sql.bind_variable(cur,':name',pName);
p := dbms_sql.EXECUTE(cur);
COMMIT;
dbms_output.put_line(p);
dbms_sql.close_cursor(cur);
END;
Run the procedure from SQL Plus as EXEC DYNSQL(1,'Saikat');
It is also possible to execute dynamic SQL using EXECUTE IMMEDATE as
shown below.
EXECUTE IMMEDIATE(‘INSERT INTO MY_TABLE SELECT * FROM
THAT_TABLE’);
4.8 Nested table
create type objAddress as object
(HouseNo varchar2(20),
Street varchar2(200),
City varchar2(50),
State char(2),
PostCode varchar2(10))
/
create type oAddress as table of objAddress
/
create table People
(No number,
Name varchar2(100),
Address oAddress)
nested table Address store as tbAddress;
insert into people values (1,'Saikat Basak',
oAddress(objAddress('100','East West
Street','Kolkata','WB','700005')))
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/
4.9 Types of joins
Suppose we are joining two tables in Oracle.
SELECT T1.X, T2.Y FROM T1 JOIN T2 ON T1.X = T2.X
Assume, T1 is driving table (i.e. more rows than T2)
Nested Loop join
This is executed like this:
For each record in T1
find matching record in T2 where T1.X = T2.X
fetch that record into result set
Now if there is no index on column X in T2, Oracle will perform full table scan
for each record in T1.
Hash join
Oracle will load create an in-memory index (known as hash table) for T2 (i.e.
smaller table)
It will still perform similar operation
for each record in T1
find matching record in T2 where T1.X = T2.X
fetch that record into result set
But even if there is no index on T2.X, Oracle will use the hash table which
works similar to index!
Clearly this is suitable only when T2 is small otherwise [1] hash table may not
fit in memory [2] creation of hash table may involve a long time (then we could
have created the index on T2 in first place!)
Sorted Merge join
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If both tables are very big, hash join is not suitable due to memory/time
requirement and nested loop will be slow or will result in full table scan.
The alternative way to speed up performance is to use sorted merge join.
In this case, both tables are sorted by Oracle (using temporary table space) by
joining key (X in this case).
The advantage is, when joining two tables, Oracle just needs to scan only a
small part of the table (e.g. as they are sorted, to find a record in T2 when T1.X
= 15 will require Oracle search just from X=10 to X=20 in T2 as it cannot be
beyond this range and so on).
The trade off is, it will take some resource (space/time/memory) to sort the
tables.
Usually Oracle chooses best method of join based on statistics available.
However, user may force using a different type of join using hints like
use_hash(T1,T2) etc.
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4.10 External tables
By creating external tables, you can run SQL statements on simple delimited
text files! However, external tables are read only i.e. you can’t update their data
using SQL (you need to modify them in text editor).
To create an external table, first you need to create a folder in your hard disk
where you will place the text files.
CREATE OR REPLACE DIRECTORY EXT_TABLES AS
'E:ORACLEORADATAEXTERNAL_TABLES'
The user, who will access external table, should have CREATE ANY
DIRECTORY system privilege.
Now create the external table in SQL Plus as –
CREATE TABLE AIRPORT_CODE
(
CODE VARCHAR2(3),
CITY VARCHAR2(100),
COUNTRY VARCHAR2(50)
)
ORGANIZATION EXTERNAL
(
TYPE ORACLE_LOADER
DEFAULT DIRECTORY EXT_TABLES
ACCESS PARAMETERS
(
RECORDS DELIMITED BY NEWLINE
FIELDS TERMINATED BY '|'
MISSING FIELD VALUES ARE NULL
)
LOCATION ('AIRPORT.TXT')
)
REJECT LIMIT UNLIMITED
You can now run SQL on the table.
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5 DBMS Packages
5.1 DBMS_JOB
Check JOB_QUEUE_PROCESSES parameter has non-zero value in
initialization file.
BEGIN
SYS.DBMS_JOB.SUBMIT(
JOB => :JOB,
WHAT => 'BEGIN UPDATE_ALL_TRANS_PRICE; END;',
NEXT_DATE => TO_DATE('11-06-2004 09:54:15', 'DD-MM-YYYY
HH24:MI:SS'),
INTERVAL => 'SYSDATE+15/1440');
COMMIT;
END;
5.2 UTL_FILE
A sample procedure to unload a table data to a text file using UTL_FILE
package is shown below.
Set UTL_FILE_DIR = ‘E:ORACLEORADATAUNLOAD’ (or path where
from you need to read/write) in initialization file.
CREATE OR REPLACE PROCEDURE UNLOAD_TABLE (piTable IN VARCHAR2)
AS
CURSOR cTable IS
SELECT * FROM category;
f utl_file.file_type;
buf VARCHAR2(200);
BEGIN
f:=UTL_FILE.FOPEN('E:ORACLEORADATAUNLOAD','CATEGORY.TX
T','w');
FOR i IN cTable LOOP
buf:=i.CategoryNo || '|' || i.Description || '|' ||
i.ParentCategoryNo;
UTL_FILE.PUT_LINE(f,buf);
END LOOP;
UTL_FILE.FCLOSE(f);
DBMS_OUTPUT.PUT_LINE('TABLE UNLOADED');
EXCEPTION
WHEN OTHERS THEN
DBMS_OUTPUT.PUT_LINE(SQLERRM);
- 71 -

END;
/
Similarly, GET_LINE is used to read data from file.
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6 Useful scripts for DBAs
6.1 To show primary/foreign key relationships of all tables and views in
a given schema
SELECT
D.TABLE_NAME "Table name",
D.CONSTRAINT_NAME "Constraint name",
DECODE(D.CONSTRAINT_TYPE,
'P','Primary Key',
'R','Foreign Key',
'C','Check/Not Null',
'U','Unique',
'V','View Cons') "Type",
D.SEARCH_CONDITION "Check Condition",
P.TABLE_NAME "Ref Table name",
P.CONSTRAINT_NAME "Ref by",
M.COLUMN_NAME "Ref col",
M.POSITION "Position",
P.OWNER "Ref owner"
FROM
DBA_CONSTRAINTS D
LEFT JOIN
DBA_CONSTRAINTS P
ON (D.R_OWNER=P.OWNER AND
D.R_CONSTRAINT_NAME=P.CONSTRAINT_NAME)
LEFT JOIN
DBA_CONS_COLUMNS M
ON (D.CONSTRAINT_NAME=M.CONSTRAINT_NAME)
WHERE
D.TABLE_NAME
IN (
SELECT TABLE_NAME FROM DBA_TABLES WHERE
OWNER=UPPER('mkm')
UNION ALL
SELECT VIEW_NAME FROM DBA_VIEWS WHERE OWNER=UPPER('mkm')
)
ORDER BY 1,2,3
6.2 To see all objects in a table space file
SELECT
D.OWNER,D.SEGMENT_NAME,D.SEGMENT_TYPE,D.TABLESPACE_NAME,
D.HEADER_FILE,V.NAME
FROM
Dba_Segments D
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JOIN V$DATAFILE V ON (D.HEADER_FILE=V.FILE#)
WHERE
D.OWNER IN ('MKM')
6.3 Which user executing what type of command
SELECT
SID,
SERIAL#,
v.schemaname,
DECODE(COMMAND
,0,'None'
,2,'Insert'
,3,'Select'
,6,'Update'
,7,'Delete'
,8,'Drop'
,26,'Lock Table'
,44,'Commit'
,45,'Rollback'
,47,'PL/SQL Execute'
,'Other') command
FROM V$SESSION v
6.4 Get output of a query to a text file from SQL Plus
set pagesize 5000
set linesize 5000
spool F:TEMPOUTPUT.TXT
set colsep "|"
select * from MKM.PRODUCT;
set colsep " "
spool off
set pagesize 50
set linesize 200
6.5 To see size of your tables and indexes
select SEGMENT_NAME, SEGMENT_TYPE, BYTES from USER_SEGMENTS
where segment_type IN ('TABLE','INDEX')
6.6 To see free spaces in table spaces
SELECT b.tablespace_name, b."Total MB", ROUND(b."Total MB" -
a."Free MB",2) "Used MB",
a."Free MB", ROUND(((b."Total MB"- a."Free
MB")/b."Total MB")*100,2) "% used"
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FROM (
(SELECT f.tablespace_name, ROUND(SUM(f.bytes/(1024*1024)),2)
"Free MB" FROM dba_free_space f
GROUP BY f.tablespace_name) a
RIGHT JOIN
(SELECT d.tablespace_name, ROUND(SUM(d.bytes/(1024*1024)),2)
"Total MB" FROM dba_data_files d
GROUP BY d.tablespace_name) b
ON a.tablespace_name = b.tablespace_name
)
ORDER BY 1
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7 New features of 10/11g
Which are not covered in this book so far. Any feature which is introduced in
10g, is also available in 11g with usually more options.
Flashback query with changing data
You already have flashback query option in Oracle 9i where you can query
snapshot of old data from undo table space. But in 10g, you can examine how
values changed between two time points.
You can query yesterday’s version of table data as:
SELECT * FROM PRODUCT AS OF TIMESTAMP SYSDATE-1
Rollback monitoring
In 9i, you can’t tell easily how much time it is going to take to rollback a large
transaction (until it is complete, the locks acquired by the transaction won’t be
released). In 10g you can simply get this vital information from
V$SESSION_LONGOPS view.
Improved table space management
10g automatically creates a SYSAUX table space during database creation. It is
used to hold data for several of Oracle’s support schemas like DBSNMP, ODM
etc.
Flashback table
In 9i, to restore a dropped table you need to use import from back up or do
incomplete recovery. In 10g, when a table is dropped, it goes to Oracle’s
Recycle Bin and you can easily restore it from there! You can run following
command from SQL Plus.
SELECT * FROM DBA_RECYCLEBIN
To restore the table use – FLASHBACK TABLE schema.table_name TO
BEFORE DROP
Hey that’s easy!
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SQL Plus improvements
Several enhancement has been made to SQL Plus like prompting, improved file
manipulations, fast DUAL optimization plan etc.
Automatic Storage Management (ASM)
In 9i, disk storage consideration (like RAID, stripping, logical grouping etc.)
was done manually. From 10g it can be done automatically with the help of
ASM.
RMAN improvement
Several enhancements have been made for incremental backup methods.
Auditing improvements
Now auditing can be performed at very detail level (FGA – fine grained audit).
In 10g, auditing will show you what user made exactly what changes to data.
Wait interface
Data dictionary views now show more information regarding on user wait
events, which will help to diagnose wait problems better.
Materialized view improvement
Oracle introduces materialized view advisor feature, which helps tuning
materialized views. Now Oracle server can decide whether to rewrite the
materialized view or not dynamically.
Model clause
Using MODEL clause in SQL, you can treat multidimensional data as an array
in memory where you can apply spreadsheet like calculations!
Enterprise Manager (EM) changes
Its architecture has been changed in 10g. It’s now installed as an HTTP server
(instead of as a client tool in 9i). So, you will use it inside browser! Moreover
lots of new features have been added. See section 1.6 for more information.
Virtual Private Database improvements
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VPD was also in 8i and 9i. But in 10g, it has improved to support a variety of
requirements, such as masking columns selectively based on the policy and
applying the policy only when certain columns are accessed. VPD has not been
discussed so far in this book. It is a method to implement security at finer grain.
For example, if you want to implement that logged on user will only see his
own records in database (e.g. seeing only his salary information from salary
table), VPD can be set up in such a way that “where username = USER” will be
automatically added to SQLs.
Segment management
Segment spaces can be managed more efficiently. Wastage of space in segments
is minimized. DBAs will have more control over space allocation.
Transportable table space
In 9i, transportable table spaces can be plugged in to other databases only if
they run on same platform. In 10g, they can be plugged to database even
running on different platforms. This is very helpful for data movement across
different systems. Another improvement is that, data can be unloaded from
tables in very fast manner (in non-text format, though) but the unloaded file,
again, can be used across platforms.
Automatic shared memory management
The space allocation for DB buffer cache, shared pool, large pool and Java pool
can be set to manage automatically and dynamically as and when required (i.e.
depending on the database workload)!
Scheduler
Usually dbms_job can be used only to run PL/SQL programs. However, the
newly introduced dbms_scheduler can even run OS commands at specified
time/interval.
Database replay
Starting from 11g, you now have option of capturing work load from a
production database and replay that on test database to simulate live conditions.
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7.1 What is g in Oracle's grid computing?
Oracle defines grid computing like this: with grid computing, groups of
independent, modular hardware and software components can be connected and
rejoined on demand to meet the changing needs of businesses.
What does it exactly mean?
We already know what is parallel computing. A complex task is divided into
smaller parts and each part is processed independently by a computer. Then the
outputs are combined to get final result.
How does grid computing differ from this parallel computing?
Grid computing is an abstract (or virtualization, as Oracle says) concept. A grid
can be an infrastructure grid, an application grid, an information grid and so on.
What – getting more confused? Ok, please read on.
In early days (~1980s) of database, the relational database management was
starting to gain popularity. In RDBMS terms, a customer buys products and a
transaction is generated. All these info like customer, product, transaction etc.
are stored in RDBMS. They are linked together (by foreign keys, in 3rd
normal
form). So from a high level view, customer, product, transaction are all part of
RDBMS.
Now come to the present days. We are gathering data like never before! Besides
RDBMS, we now have lots of different stuffs like OLAP (Business Intelligence/
Data Warehouse etc.), OLTP (transactional data), BPEL (Business Process
Execution Language), Web services (using XML), OWB (Oracle Warehouse
Builder) etc.
The grid is collection of all these - i.e. different applications and data which
speak with one another.
Oracle has product of almost everything nowadays – which is wrapped around a
fuzzy name called Fusion Middleware. These components are designed so that
one component (say OWB) can interact with another (say core Oracle database).
This constitutes an architectural grid.
The relational data on your RDBMS can be termed as information grid.
There's another aspect of grid. Let us take Oracle Real Application Cluster or
RAC. Here multiple instances of database are inter-connected to safeguard
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single point of failure. This is an example of infrastructure grid. Everything is
part of grid. It is a concept. It could have been told as Matrix computing too.
(Did you enjoy Matrix series of movies?)
Now you know what the buzzword Grid computing mean!
7.2 What are Oracle Fusion Middleware (OFM) and Service Oriented
Architecture (SOA)?
If you are not sure about what are these things and try to have a look at Oracle's
website, there is a good chance that you might find yourself confused.
That's quite expected. Oracle's website is for marketing their product. It's not
their interest to describe their products in a way that people think it is there is no
magic about it!
So, here I try to explain the things in non-geeky terms.
The Fusion Middleware consists of Oracle's non core-database products – some
of which are not actually middleware!
This includes Oracle's Developer suite (Forms & Reports), Java related tools,
web logic server, content management etc. OFM depends on open standards
such as BPEL, SOAP, XML and JMS.
Oracle SOA is a part of OFM.
What is SOA?
The main essence of SOA is that applications will talk with each other in a
language (i.e. data format, process steps) which is understood by all others
applications communicating with.
SOA is about reuse.
SOA helps business to move, change, partner and re-invent itself with ease and
grace.
SOA extends idea of reuse not only to web services but also with business
services.
SOA components are loosely coupled.
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SOA can contain web service, BPEL etc.
Web service
Example, you throw a postcode to Yahoo Geo-coder and it gives you back
latitude, longitude of that post code.
You ask for price of particular item to a website, it supplies you the price.
Usually, web service results are returned in XML format to ensure universal
compatibility.
In SOA segment, you will often hear the term Orchestration. What does it
mean?
If you seen an orchestra, you know that conductor just draws some invisible
drawings in mid air by moving his magic wand from one side to another.
However, musicians can decipher his rhythm and plays their instruments so that
every one plays same tune at same pace.
Orchestration in SOA has similar meaning. It ensures that all applications under
SOA, know how to be in sync with other applications in the group.
But how orchestration is implemented?
It is done via BPEL or Business Process Execution Language.
BPEL is a tool, using which you can draw how data moves from one application
to another. For those who have not used it, it is like a Visio flow chart diagram
editor. But, when you draw objects in BPEL, you tell them what to do. You
instruct them where to read data from, how to process it and where to send
output after processing finished. So, basically it is a graphical tool to define
business process. Without BPEL, the whole process will look like thousands of
lines of PL/SQL (or Java or C++ or whatever) codes!
Behind the scene BPEL still writes codes - but it just make simpler (!) for any
business user to understand and define the process. Now whether that is good or
bad is debatable – I am just outlining the concept here.
So, BPEL works to integrate several applications. BPEL usually follows XML
standard as interface to several components.
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Let us take a bigger example. Your supplier sends you a file which contains all
the products, quantities and unit price you ordered for. You need to update your
inventory accordingly. Now assume that your supplier quoted the price in € but
you need to put that in £ in your database. Using absolute minimum technology,
you need to write a small program to convert € to £ while loading that data to
your system. But if you are using BPEL, you can visually draw the program!
- 82 -

8 DBA interview questions
Answers are not provided. Some questions are basic and straightforward. Some
questions are open ended. If you cover OCP curriculum, you will be able to
answer most questions. These questions are for DBAs with 3 – 8 years of
experience.
Please note that in most DBA interviews, besides core DBA questions,
candidates are usually asked some questions about the operating system (say
Unix) as well.
Concentrate on questions depending on the role actually required in the
position.
8.1 Open-ended questions
1. What DBA activities did you to do everyday?
2. What is your typical day like?
3. What other parts of your organization do you interact with and how?
4. Do you consider yourself a development DBA or a production DBA and
why?
5. What database and overall architecture would you suggest for testing new
middleware without impacting production?
6. How do you assess my database’s health?
7. How would you approach a performance problem with a three-tier
application?
8. How do you test your backup/recovery procedures?
9. How would you support the upgrade process for multiple applications,
with different application rollout cycles, in the same instance?
10.What ER tool (& version) you used?
11.What should consist of DW Team?
8.2 Technical questions
8.2.1 Set 1
1. Explain the difference between a hot backup and a cold backup and the
benefits associated with each.
2. You have just had to restore from backup and do not have any control
files. How would you go about bringing up this database?
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3. How do you switch from an init.ora file to a spfile?
4. Explain the difference between a data block, an extent and a segment.
5. Give two examples of how you might determine the structure of the table
DEPT.
6. Where would you look for errors from the database engine?
7. Compare and contrast TRUNCATE and DELETE for a table.
8. Give the reasoning behind using an index.
9. Give the two types of tables involved in producing a star schema and the
type of data they hold.
10.What type of index should you use on a fact table?
11.Give two examples of referential integrity constraints.
12.A table is classified as a parent table and you want to drop and re-create
it. How would you do this without affecting the children tables?
13.Explain the difference between ARCHIVELOG mode and
NOARCHIVELOG mode and the benefits and disadvantages to each.
14.What command would you use to create a backup control file?
15.Give the stages of instance startup to a usable state where normal users
may access it.
16.What column differentiates the V$ views to the GV$ views and how?
17.How would you go about generating an EXPLAIN plan?
18.How would you go about increasing the buffer cache hit ratio?
19.Explain an ORA-01555 (Snapshot too old)
20.Explain the difference between $ORACLE_HOME and
$ORACLE_BASE.
21.How would you determine the time zone under which a database was
operating?
22.Explain the use of setting GLOBAL_NAMES equal to TRUE.
23.What command would you use to encrypt a PL/SQL application?
24.Explain the difference between a FUNCTION, PROCEDURE and
PACKAGE.
25.Explain the use of table functions.
26.Name three advisory statistics you can collect.
27.Where in the Oracle directory tree structure are audit traces placed?
28.Explain materialized views and how they are used.
29.When a user process fails, what background process cleans up after it?
30.What background process refreshes materialized views?
31.How would you determine what sessions are connected and what
resources they are waiting for?
32.Describe what redo logs are.
33.How would you force a log switch?
34.Give two methods you could use to determine what DDL changes have
been made.
35.What does coalescing a table space do?
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36.What is the difference between a TEMPORARY table space and a
PERMANENT table space?
37.Name a table space automatically created when you create a database.
38.When creating a user, what permissions must you grant to allow them to
connect to the database?
39.How do you add a data file to a table space?
40.What view would you use to look at the size of a data file?
41.What view would you use to determine free space in a table space?
42.How can you rebuild an index?
43.You have just compiled a PL/SQL package but got errors, how would
you view the errors?
44.How can you gather statistics on a table?
45.How can you enable a trace for a session?
46.What is the difference between the SQL*Loader and IMPORT utilities?
47.Name two files used for network connection to a database.
8.2.2 Set 2
1. A user has connect and resource privileges allocated by the DBA. He is
been allocated quota on three table spaces by the DBA, - Default Table
space Quota 500 M, Table space 1 Quota 100 M, Table space 2 Quota
200 M. Now the user tries to make a table, which uses 300 M in table
space 2. Will he be successful?
2. After a table is defined, can columns be removed?
3. Can we add columns to a table, which is already defined?
4. Can you explain recovery of in a RDBMS?
5. Describe the procedure for moving a data file from one disk to another.
Show actual SQL used for this procedure.
6. Difference & when to use FIRST_ROWS & ALL_ROWS parameter,
while using an optimizer
7. Explain B-Tree index?
8. Explain composite index?
9. Explain different kind of locking in RDBMS?
10.Explain the definition of a "star schema."
11.Explain the difference between a "hot" and a "cold" backup. What is
involved with executing a "hot" backup?
12.Explain the differences between logical and physical database backups.
What are the benefits and penalties of each?
13.Explain the processing of a program using cursor?
14.Explain third normalized form?
15.Explain two phase commit?
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16.Explain what a bitmapped index is, what its applications would be, and
why it's useful.
17.Explain what an Oracle snapshot is.
18.Have you heard about Tuxedo, Encina, CICS?
19.How can one implicitly disconnect a user from the database, who is idle
for a long time? (Using Profiles)
20.Is it possible that there could be performance degradation due to so many
indexes? When and how?
21.Questions were asked about parameters in export, like: consistent = y,
(what is the purpose of it)?
22.There are 100 data files, numbered from 1 to 100. File number 10 is
deleted and it has 500 MB of data. The database is working in No-
Archive log mode. How can the database be recovered?
23.There are about a 10,000 records in a table. User 1 runs a query, which is
doing a full-table scan. While doing the full table scan, user 2 changes
some value x to y using a DML statement in record. What does the 1st
user see (x or y)? If x, then where is the value stored? (Rollback
Segments).
24.What RDBMS objects are required before you can create a table?
25.What are the contents of a Control File?
26.What are the different data structures used for indexes?
27.What are the types of recovery one can perform?
28.What can you do with an alias that you cannot do with a synonym?
29.What is Normalization?
30.What is a correlation name and explain the usage?
31.What is a cursor?
32.What is a foreign key?
33.What is a join? Explain outer join with an example?
34.What is a page in RDBMS?
35.What is a partitioned table?
36.What is a stored procedure? Why there are required?
37.What is a sub query?
38.What is a synonym?
39.What is a view?
40.What is commit and rollback?
41.What is distributed transaction processing?
42.What is logging in a RDBMS?
43.What is primary key?
44.What is query execution plan?
45.What is query optimizer?
46.What is referential integrity?
47.What is the SQL statement necessary to delete a user named "Joe" and
everything that he owns in a database?
- 86 -

48.What is the difference between a searched update and a positioned
update?
49.What is the difference between static SQL and dynamic SQL?
50.What is the importance of redo log files?
51.What is the save point in a transaction?
52.What is the use of LIKE?
53.What is the use of the parameter "MAXTRANS”. Is it used at block level,
extent level or segment level?
54.What is transition monitor?
55.What is transaction? Explain atomic property of a transaction?
56.What variables in the "INIT.ORA" file affect the amount of RAM needed
for the SGA?
57.What's the default password for the Oracle user "Scott"?
58.Where and when can we use the HAVING clause?
59.Which SQL error will you get when you try to fetch data from a cursor
after it has run out of data?
60.Which parameter can be used to enable check pointing at regular intervals
(FAST_START_MTTR_TARGET)?
61.Which parameter do you use to read multiple blocks in one go
(DB_MULTIBLOCK_READ_COUNT)
62.Why a stored procedure supposes to give better performance?
63.Why indexes are so important?
64.Why is the difference between Direct Path Export and Conventional Path
Export?
65.Why it is bad to use the SELECT * in static SQL?
66.Why row level locking is desired?
67.Why would you use UNION instead of a JOIN?
8.2.3 Set 3
1. What data warehouse features are there in Oracle 9i?
2. What is the difference between B-Tree & Bitmap index? Explain.
3. What is dimension table?
4. What is surrogate key?
5. What is 3rd normalization?
6. What is ref cursor?
7. What is materialized view?
8. What is query rewrite?
9. What is inline view?
10.What is conformed dimension?
11.What is slowly changing dimension?
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12.How ER diagram differs from DW dimension? (Answer – OLTP schema
vs. Star schema)
13.What is type1, type2, type3 related to dimension?
14.What is the difference between top down and bottom up approach?
15.When is full-table scan beneficial?
16.What performance tunings you have done?
17.Update Emp set salary=5000 where id=100 – explain all steps that
happens internally.
18.State differences between 8i and 9i?
19.State differences between 9i and 10g?
20.What parameters of database you can't change without recreating one?
(Answer – block, buffer, and character set etc.)
21.What is asynchronous PL/SQL block?
22.What Oracle books you read?
23.What is autonomous transaction?
24.What are various types of transactions?
25.What extra Oracle features you like to see?
26.Explain B Tree & Bitmap index.
27.Explain clearly what will happen if I index a gender column using B tree
instead of Bitmap.
28.What is basically stored in index?
29.If a table has no rows, does it take any space?
30.What largest database you have handled? How many tables were there?
31.What is two phase commit?
32.What is distributed database?
33.What is RAC & what is its advantage?
34.How do you handle exception in PL/SQL procedure?
35.What is the advantage or package over procedure?
36.What is pragma-restricted function?
37.What are Coyd's golden rules (not about normalization)?
38.How do you suggest backup strategy of production database?
39.What database challenges you faced in your last project?
40.What is 2nd normalization?
41.When do you de-normalize data?
42.What database tuning you have done?
43.What is the length of rowid data?
44.What Oracle analytic functions you have used?
45.Can you specify sequence in SQL loader?
46.Explain direct/indirect load?
47.What are different components of SGA? What are different background
processes? What are functions of each of them?
48.What is Reco process?
49.How do you see all columns of all tables?
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50.Explain implicit & explicit cursor.
51.How do you declare record type variable?
52.What is PL/SQL table? Define it's syntax.
53.How do you select duplicate rows from a table?
54.How do you avoid fragmentation?
55.Explain deadlock with an example.
56.Why people sometimes don't run database in archive log mode?
57.What does DBWR & LGWR do?
58.Who write data in database buffer cache & redo log buffer?
59.Can you get back sequence values already generated?
60.Explain shared server concept.
61.When a new session starts, how do you see extra processes created from
data dictionary tables?
62.Where do you find all database objects?
63.Where the source of function/procedures is stored?
64.What do you know about Standby database & Replication?
65.What are different types of backups?
66.Explain all steps of complete & incomplete recovery.
67.What are various types of recoveries? Explain.
68.What database tuning you have done?
69.What tuning tools you have used?
70.What database design you have performed?
71.What backup method you suggest for a 24x7 production database?
72.Explain some tuning methods.
73.Explain various components of SGA.
74.Where does init.ora reside?
75.Did you install Oracle server?
76.When do you go for import/export instead of backup?
8.2.4 Set 4 (SQL)
1. What is wrong with following query: SELECT column1, column2,
AVG(column3), column4 FROM table1 GROUP BY column1, column2
2. What is wrong with this query: SELECT AVG(COUNT(employee_id)
FROM employee GROUP BY dept
3. How do you delete duplicate rows from a table using SQL? [Ans – delete
from dup_test d1 where rowid not in (select max(rowid) from dup_test d2
where d1.num = d2.num)]
4. How do you identify duplicate rows in a table?
5. A table has following columns – deptartment, employee_name and
salary. How do you list average salary of all departments?
6. How do you find database’s time zone? [select dbtimezone from dual]
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8.3 Questions you should ask
What processes do you follow while implementing changes in production?
Beside the DBAs and system administrators, who has access to the "Oracle"
operating system account?
How often is the oracle operating system account password changed?
Are the DBAs co-located with the teams they support?
How is capacity planning performed?
Is there adequate capacity already in place to support the expected growth over
the next year?
Is there a formal job definition for the DBA role?
Is there a defined technical career path?
How is IT aligned with the business areas?
How many employees report to more than one manager?
How do you determine if a DBA has been successful?
How are the application DBAs and production control DBAs organized?
- 90 -

9 References
• Oracle classroom course presentations
• OCA/OCP Oracle books (DBA I, DBA II, Performance Tuning, SQL)
from BPB publications.
• Oracle manuals
• Oracle Press DBA and PL/SQL books
• Classroom course at SQL Star International, Calcutta.
• http://download.oracle.com/docs/cd/B28359_01/rac.111/b28252.pdf
• http://www.oracle.com/technology/pub/articles/chan_sing2rac_install.ht
ml
• http://www.orafaq.com/wiki/RAC_FAQ
- 91 -

10 Oracle server’s diagrammatic overview
- 92 -
SGA
Database buffer cache
Keep
Recycle
Default
Redo log buffer cache
Large pool (optional)
Java pool (optional)
Shared pool
Data
dictionary
cache
Control
structures
Library cache
Shared SQL
PL/SQL
procedures
& packages
Locks and
other
structures
Redo log files User
connection
Server process created
for user’s connection
Data files – System &
Sysaux table space,
Undo table space,
Application data table
spaces etc.
Parameter file
(Read when
database starts)
P
G
A
Control file –
synchronization information
for all Oracle files

Oracle dba-concise-handbook

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