ibm db2 using oracle skills

8/2/2019 IBM DB2 Using Oracle Skills

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IBM DB2 e-kit for Database Professionals

Learn how easy it is to get trained and certified for DB2 for Linux, UNIX, and Windows with theIBM DB2 e-kit for Database Professionals.Register now, and expand your skills portfolio, or

extend your DBMS vendor support to include DB2.

In anearlier developerWorks articlewe talked about how to leverage your MS SQL Server 2000

skills to learn DB2. Is your background in Oracle rather than SQL Server? If so, read on. In thisarticle, we will show you how to use your current knowledge of Oracle 10g to quickly gain skills

in DB2 9.

On July 28 2006, IBM made available DB2 9 for Linux, UNIX, and Windows, a truly hybrid

data server that meets today's rigorous business demands. DB2 9 is the only data server today to

use pureXML technology that allows you to store XML natively, that is, internally inhierarchical format. Other features include row compression, label based access control (LBAC)security, and autonomic features such as the Self-tuning Memory Manager (STMM). This article

starts with a comparison of DB2 and Oracle, and then focuses on introducing the new featuresavailable in DB2 9.

Note: For the remainder of this article, we will use the term "Oracle" to refer to Oracle 10g

Release 2 and "DB2" to refer to DB2 9 for Linux, UNIX, and Windows.

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Overview of system structures

To start out, we need to understand the architecture used by Oracle and how it compares withDB2.Figure 1shows the system structure of Oracle. Compare it withFigure 2, which shows the

system structure of DB2. Refer back to these figures for understanding as you read the article.

Figure 1. Oracle system structure on Linux, UNIX, and Windows Version 10.2
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Figure 2. DB2 on Linux, UNIX, and Windows system structure


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Instances

The concept of an instance is similar in both Oracle and DB2. In both cases an instance is acombination of background processes and shared memory. The major difference between the

two is that in Oracle there can only be one database per instance, while in DB2 multiple

databases can share an instance.

Because there is a one-to-one correspondence between database and instance, in Oracle youcreate an instance implicitly by creating a database with the CREATE DATABASE command.

Alternatively, to create an Oracle instance on your machine you can use the Database

Configuration Assistant, or you can use the ORADIM utility, available with Oracle 9i with the

NEW option. You must also provide certain information including a System Identifier (SID) or a

service name, instance password, maximum number of users, startup mode, and so on. Similarly,to delete the instance the ORADIM utility can be used with the DELETE option. You would

need to pass in either the SID or the service name. There is no default instance created with a

fresh install of Oracle unless you create a new database during the installation process.

In DB2, after installing the product on the Windows platform, the instance "DB2" is created by

default. In Linux and UNIX, the default instance name is called "db2inst1". To create another

instance in the same machine, you simply execute the command db2icrt .

Figure 3shows the default DB2 instance "DB2" (in Windows) and two other instances created

with the db2icrt command from the DB2 Control Center GUI.

Figure 3. DB2 Control Center GUI showing DB2 instances

To reference a given DB2 instance from a command line interface, use the environment variable

DB2INSTANCE. This variable lets you specify the current active instance to which all

commands would apply. For example, if DB2INSTANCE is set to PROD, and then you issue the

command create database MYDB1, you will create a database associated with instance PROD.If you wanted to create this database on instance DB2 instead, then you would first have to

change the value of the DB2INSTANCE variable to DB2. This is similar to the ORACLE_SID(System Identifier) which is also used when users want to switch between instances.
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Another easy way to identify the instance you want to work with is by using the DB2 Control

Center GUI as shown inFigure 3.To see an entry for the new instance in this tool, you may haveto add the instance to the GUI by right clicking on Instances and choosing Add. To drop an

instance in DB2, you can execute the command db2idrop .

In summary, in Oracle the Database Configuration Assistant can be used to create, modify, start,stop and delete the instance, while in DB2 the Control Center GUI can be used for a similarpurpose. Also an Oracle instance can only have a one-to-one relationship with a database, while

in DB2 this is not the case. Multiple databases can exist and be concurrently used in a DB2

instance.

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Databases

In Oracle, a database can either be created manually using the CREATE DATABASE commandor by using the Database Configuration Assistant. Creating the database manually requires that a

series of steps be followed, including setting OS variables, preparing the parameter file, and

creating a password file before the CREATE DATABASE command can be executed.

Metadata information is stored and managed by the Data Dictionary, which is composed of base

tables, and corresponding views. The base tables are created automatically during databasecreation, and the views are constructed by running the catalog.sql and catproc.sql scripts.

The Oracle database is therefore seen as a collection of 3 file types:

1. Data File: Contains actual data, physical implementation of the database. (Similar toContainers in DB2)

2. Redo File: This is equivalent to Transaction Logs in DB2.3. Control File: Contains information to maintain and verify database integrity.

In DB2, an instance can contain several databases, as shown inFigure 2. Each database is a truly

closed and independent unit. Each database has its own catalog table space, temporary table

space, and user table space which are created by default upon successful database creation. DB2does contain a binary file known as the system database directory that contains entries of all the

databases you can connect from your DB2 machine. This directory is kept at the instance level.

When an instance is created, no databases are created by default. You need to explicitly create a

database using the create database command. You can also create a database using the Control

Center as shown inFigures 4and5.

Figure 4. Creating a DB2 database using the Control Center GUI
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Figure 5. Creating a DB2 database using the Control Center GUI (continued)

InFigure 5, you can also see what happens when you clickShow Command. All DB2 Control

Center GUI screens let you see the SQL statement or command that is actually executed in the

background. These commands can be saved in scripts for execution at a later time, or can be
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copied and executed from the Command Line Processor (CLP) tool or Command Center GUI

tool. These tools are equivalent to Oracle's SQL*Plus and iSQL *Plus respectively.

A DB2 database can be dropped by using the 'DROP DATABASE' command or from the DB2

Control Center GUI. In Oracle there is no such command; a database is deleted by deleting all

the associated datafiles.

Databases within an instance normally don't interact with each other. However, if your

application needs to interact with more than one database, this requirement can be supported by

enablingfederation support. See theresourcessection for an article about federation.

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Containers, table spaces, bufferpools and pages

In Oracle, data is physically stored in files called Data Files. This is similar to DB2's containers

where data is physically stored. Every Oracle database contains a table space named SYSTEM,which Oracle creates automatically when the database is created. Other table spaces for user,

temporary and index data need to be created after the database has been created, and a user needs

to be assigned to these table spaces before they can be used.

In DB2, a table space is the logical object used as a layer between logical tables and physicalcontainers. When you create a table space, you can associate it with a specific buffer pool(database cache) as well as to specific containers. This gives you flexibility in managing

performance. For example, if you have a "hot" table, you can define it in its own table space

associated with its own buffer pool. This helps ensure the data for this table is continuouslycached in memory.

In DB2 three default table spaces are created automatically upon database creation when usingdefault values for the CREATE DATABASE command.Table 1describes the default DB2 table

spaces:

Table 1. DB2 table spaces created by default when a database is created with default values

Table space

NameDescription

SYSCATSPACE Catalog table space containing metadata.TEMPSPACE1

System temporary table space used to perform operations such as joins and

sorts. The name of this table space can be changed.

USERSPACE1This table space is optional and can be used to store user tables when a table

space is not explicitly indicated at table creation time.

Because databases in DB2 are independent units, table spaces are not shared across databases.

Since they are only known within a database, two different databases can have table spaces of
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the same name. You can see this inFigure 2where database MYDB1 has a table space named

MYTBLS and database MYDB2 has a table space of the same name.

DB2 table spaces can be classified as SMS (system-managed spaces) or DMS (database-

managed spaces). SMS table spaces are managed by the operating system and can only be

directories. They grow automatically as needed; thus SMS provides good performance withminimum administration. DMS table spaces are managed by DB2, and can be files or raw

devices. This type of table space allows for best performance, but some administration isrequired. For example, you need to specify ahead of time the amount of space you want to

allocate for the table space, because growth is not automatic.

Oracle does not have the SMS concept for its storage model but its data files are similar to DB2

DMS table spaces. That is, you can increase a database size by either adding a datafile to the

table space, by increasing the size of the data file, or by adding a new table space.

Table 2below shows how Oracle databases or table spaces map to DB2 databases or table

spaces.

Table 2. How Oracle databases map to DB2 databases and table spaces

Oracle database or table space DB2 database or table space

SYSTEM is the table space that

holds the catalog (Data Dictionary)information.

SYSCATSPACE (catalog table space); as in Oracle, this

information is kept only at the database level.

Data Dictionary (contains metadata

in form of tables and views) andresides inside the SYSTEM table

space.

System Catalog Tables (identified by the SYSIBM schema)

and system views (identified by the SYSCAT ORSYSSTAT schema) and reside inside the SYSCATSPACE

table spaceSCOTT database SAMPLE database

TEMP table spaceSystem Temporary table space (By default it is calledtempspace1)

UNDO table space N/A

USER table spaceUser table space. By default, USERSPACE1 is normallycreated after database creation

As indicated earlier, Oracle's data buffer concept is equivalent to DB2's bufferpool; however,DB2 allows for multiple bufferpools to exist. There is no predefined number of bufferpools that

you can create, and they can have any name.

The concept of an Oracle blockis most similar to DB2's page. A DB2 page can have a size of 4k,

8k, 16k or 32k. A table row must fit in only one page; it cannot span to other pages as in Oracle.

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Object names

An Oracle object name takes the following form:

[Schema_name.]object_name[@database]

In DB2, objects also have a two-part structure:

Schema_name.object_name

As in Oracle, the DB2 schema name is used to group objects logically. An important difference,however, is that in DB2, a schema name does not have to match to a user id. Any user with a

privilege called IMPLICIT_SCHEMA can create an object using a non-existing schema. For

example, suppose that "Peter" has IMPLICIT_SCHEMA privilege and executes this command:

CREATE TABLE WORLD.TABLEA (lastname char(10))

In this case, the table WORLD.TABLEA is created, where WORLD is the newly createdschema. If Peter had not explicitly indicated the schema, then the table PETER.TABLEA would

have been created, because the connection ID is used by default.

In DB2 you always connect to a database before issuing database specific commands; therefore,

under this architecture, object names need not include the database name.

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Tables, views, and indexes

Tables, views and indexes are basically the same in both Oracle and DB2.

DB2 provides a utility called Design Advisor which can be used to recommend indexes for a

particular query or workload. The Design Advisor can be invoked from the DB2 Control Center

or from the DB2 CLP using the db2advis command. In DB2, indexes are directly tied to the tabledefinition. For example, when using DMS table spaces you can specify in which table space the

indexes can reside as follows:

CREATE TABLE mytable (col1 integer, col2 char(10)) in tbls1 index in tbls2

The above example shows that the data for the table will be stored in table space 'tbls1', while the

index pages will be stored in table space 'tbls2'. This is in contrast to Oracle syntax where theCREATE INDEX statement provides an option to specify in which table space the index will

reside.

Also, once an index has been created in DB2, you cannot alter any clause of the index definition.

You would need to drop the index and create it again in order to implement changes.
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As in Oracle, DB2 tables, views and indexes in different databases can have the same names.

Tables and views within the same database must have distinct names, but creating an index withthe same name as either an existing table or view is allowed.

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Stored procedures, triggers and user-defined functions (UDFs)

DB2 stored procedures can be written in any language supported by the DB2 precompilers,

including Java, C, C++, REXX, Fortran, and COBOL. However, the recommended language touse is the SQL Procedural Language (SQL PL), which is fairly similar to Oracle's PL/SQL. SQL

PL stored procedures are easy to create and have good performance. DB2 stored procedure

development also supports SQLJ and Java using JDBC drivers type 2 and 4. Type 3 is

discontinued.

DB2 stored procedures can be written in any language supported by the DB2 precompilers,

including Java, C, C++, REXX, Fortran, and COBOL. However, the recommended language touse is the SQL Procedural Language (SQL PL), which is fairly similar to Oracle's PL/SQL. A C

compiler is needed to develop SQL PL stored procedures, as these are first translated into C. A C

implementation of stored procedures may provide performance advantages because the code is

compiled once (especially if run in unfenced mode); however, it also adds the requirement ofhaving this compiler on the development system. In a future release of DB2, support for SQL PL

stored procedures without the need of a C compiler is expected. DB2 stored procedure

development also supports SQLJ and Java using JDBC drivers type 1 through 4.

Development of triggers and functions can use inline SQL/PL, a subset of SQL PL. The DB2Developer Workbench tool can be used to easily create, build, debug and deploy DB2 storedprocedures and user-defined functions.

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Configuration files

Traditionally Oracle stores all session and system-related parameters in a text file, normally

referred to as initSID.ora. However due to the non-persistent nature of this text file, starting fromOracle 9i, Oracle introduced Server Parameter File (SPFILE), which is a binary parameter file

stored on the server. This persists across instance shutdown and startup. The initSID.ora file isstill used, however, when an SPFILE is not available. Prior to the introduction of SPFILE, any

ALTER SYSTEM and ALTER SESSION commands that affected parameters would only persist

during that instance or that session. The DBA would have had to manually modify theinitSID.ora text file whenever a rebound of a database instance was intended. Network access

configurations are typically stored in listener.ora for listener and tnsnames.ora for client access.
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With DB2, configuration parameters are also stored at the instance level, known as the database

managerconfiguration file, and at the database level, known as the database configuration file.Most of these parameters can be changed dynamically, that is, there is no need to stop and restart

the instance or force all connections before the change to the parameter value takes effect.

If you would like to manually change a specific database manager parameter from the CLP, usethe command UPDATE DBM CFG USING .

If you would like to manually change a specific database parameter from the CLP, use the

command UPDATE DB CFG FOR USING .

These commands would be the equivalent to Oracle's ALTER SYSTEM and ALTER SESSION.

Alternatively, using the Control Center, you can review and change values for these parameters;

if you right click on a given instance and choose Configure Parameters, you will see the

window shown inFigure 6.

Figure 6. DB2 Database Manager configuration parameters (instance level)

At the database level, right clicking on a given database, and choosing Configure Parameters

displays the window shown inFigure 7.
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Figure 8. - DB2 Configuration Advisor

In addition to configuration files, DB2 also uses DB2 Registry variables normally for platform-specific configurations. Note, the DB2 Registry variables have no relationship whatsoever to the

Windows registry. Use the command db2set to review and change these variables.

Connectivity (network access) information is stored in the System database directory, local

database directory and node directory. These are binary files and can only be modified with the

CATALOG and UNCATALOG commands.

Back to top

Memory architecture and background processes

Next we'll look at the memory architecture and background processes, and will compare andcontrast the way they are used in Oracle and DB2.
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Figure 9: Oracle memory architecture and background processes

The System Global Area (SGA) in Oracle is a group of shared memory areas that storesinformation for the instance. Examples include statement cache, redo log buffers, and data buffer

cache. The Program Global Area (PGA) and the User Global Area (UGA) shared memory areascontain data and control information for server processes and user sessions.

Oracle supports multiple instances within the same machine but background processes are not

shared. For example, three instances in one machine will require three set of backgroundprocesses. Therefore it is generally recommended to have one database, one instance and

multiple schemas within the same machine.


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Figure 10: DB2 Memory architecture and background processes

Both DB2 and Oracle use shared memory areas, but DB2's memory architecture is implementedin a slightly different way than Oracle's. Since a DB2 instance can contain more than one

database, two levels of configuration exist. As we mentioned in the previous section, instance

level configuration can be done in the DBM CFG file while the database level configuration isdone in the DB CFG file. Configuration parameters at both levels can be adjusted to tune

memory usage. The section below provides a bit more detail on DB2's memory structures and

different background processes.

Unlike Oracle where memory is allocated to both the instance and the database upon startup,

DB2 allocates memory at different levels. This is primarily due to the fact that a DB2 instance

can contain multiple databases. There are three main memory structures in DB2:

Instance shared memory: This refers to the database manager global shared memory,which is allocated when the instance is started using the db2start command, and

remains allocated until a db2stop command is issued to stop the instance.

Database shared memory: This refers to the database global memory, which is allocatedwhen the database is activated or connected to for the first time. Memory allocatedincludes buffer pools, locklist, database heap, utility heap, package cache and catalog

cache.


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Application shared memory: This refers to the memory allocated when an applicationconnects to a database and is used by agents that do the work requested by the connectedclients. Each application connected to the database has memory allocated to it; therefore

accurate configuration of the parameters affecting the application shared memory

becomes crucial.

In DB2 for Windows, server activities are conducted in the form of threads, while in Linux and

UNIX environment these are implemented as background processes. DB2 processes operate inthe following levels:

Instance Level: These are processes that are initialized when an instance is started:1. DB2 Daemon Spawner (db2gds): Global daemon processor started for each

instance (only in UNIX)

2. DB2 System Controller (db2sysc): Main DB2 process3. DB2 Watchdog (db2wdog): Parent process for all other processes4. DB2 Format Log (db2fmtlg): Similar to the ARCn process in Oracle, pre-

allocates log files in the log path

Database Level: These are processes that are initialized when a connection is made to adatabase.

1. DB2 Log Reader (db2loggr): Similar to the subset of Oracle's PMON process.This process reads log files during rollback, restart recovery and roll forward.

2. DB2 Log Writer (db2loggw): Flushes log from log buffer to the transaction logfiles on disk. Equivalent to LGWR process in Oracle.

3. DB2 Page Cleaner (db2pclnr): Equivalent to DBWR process in Oracle, thisprocess cleans the buffer pool before pages from the disk are moved into the BP.4. DB2 Prefetcher (db2pfchr): Retrieves pages from disk and places into the bufferpool before it is needed.

5. DB2 Deadlock Detector (db2dlock): Deadlock detector process.

Application Level: Each application connecting to the database would have its own shareof application-level background processes associated with it. These are as follows:

1. DB2 Communication Manager (db2ipccm): Inter-process communicationprocess for each locally connected client.

2. DB2 TCP Manager (db2tcpcm): TCP communication manager process forremote clients connecting using TCP/IP.

3. DB2 Coordinating Agent (db2agent): Process that handles all requests on behalfof an application.

4. DB2 Subagent (db2agnta): Idle subagent.5. Active Subagent (db2agntp): Active subagent used when SMP parallelism is

enabled so that multiple processes are used for a single task.


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For a comprehensive explanation of DB2's processes please refer to the article 'Everything you

wanted to know about DB2 processes'.

Back to top

Locking mechanisms

Locking in Oracle can be either manual or automatic. The Oracle Lock Manager can implicitly

lock table data at the row level, or default locks can be overridden at transaction or session level

using the following SQL statements:1. SET TRANSACTION ISOLATION LEVEL2. LOCK TABLE3. SELECT FOR UPDATE

Oracle supports a mechanism called Multi-Version Read Consistency which is implemented by

undo data in the undo segments.

DB2 implements ANSI standard Isolation levels such as Uncommitted Read, Cursor stability,

Read stability and Repeatable Read. A user will only see committed data unless the

Uncommitted Read isolation level is used. Row locks are acquired implicitly according to the

isolation level. Database objects that are lockable are table spaces, tables and rows, however,

only tables and table spaces can be explicitly locked. The LOCK TABLE command can be used tolock a table instead of using the default row locking.

Unlike Oracle, in DB2, locks are stored in the memory and not in data pages. The LOCKLIST

database configuration parameter can be used to configure the memory available for locks, while

the MAXLOCKS configuration parameter defines the maximum amount of memory for aparticular application's locks.

Back to top

Security

Both Oracle and DB2 are secure databases with basic and advanced security features. In Oracle,

there are 4 different user authentication methods, as follows:

Database: The database performs both identification and authentication of users. External: The operating system or network service performs authentication Global authentication and authorization: The user is authenticated globally by SSL Proxy authentication and authorization: The middle-tier server performs

authentication.
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The authentication method is specified when creating the user using the CREATE USER command.There are several Data Dictionary views that contain information about these users.

In DB2, users do not exist within the database, but are rather managed by the operating system.

No database login information is kept in any database table. Any operating system user can

potentially access DB2; however, unless they have been granted a given DB2 authority orprivilege, there is not much they can do. Granting and revoking authorities and privileges caneasily be handled through the Control Center GUI. You first may have to add a user or group to

the Control Center from the available operating system users or groups.

Also in DB2 the term "roles" is not used; instead, DB2 uses the term "authorities", which are

similar to Oracle's database roles, whereby privileges are granted to certain groups or users. Theauthorities supported with DB2 are: SYSADM, SYSCTRL, SYSMAINT, SYSMON, SECADM,

DBADM and LOAD.

The SYSADM, SYSCTRL and SYSMAINT authorities cannot be granted using the GRANT

SQL statement. These special authorities can only be set from the database managerconfiguration file.

DB2 also uses the term "privilege" which is similar to Oracle's system and schema object

privileges. There are database privileges (connect, createtab, and so on) and database object

privileges (schema, table, view, and so on).Figure 11shows DB2 security information obtainedfrom the Control Center GUI. Most of the tabs shown on the Change User window correspond to

the privileges supported by DB2.


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Figure 11. DB2 Security

Oracle 10g security remains largely the same with some enhancements. Following is a list of the

enhancements in Oracle 10g:

DML support of FGA - SQL support of fine-grained auditing (FGA) has been enhancedto support granular auditing of queries as well as UPDATE, INSERT, and DELETEoperations.

Communication over SASL - This feature provides an alternate secure channel forcommunication between Oracle Internet Directory (OID) and the database or between

two databases. If your enterprise deploys password-authenticated users, then you no

longer have to invest in and administer public key infrastructure (PKI). SimpleAuthentication and Security Layer (SASL) communication provides an equally secure

channel.

Unified user model - A single sign on user defined in the directory can now use thefeatures offered by Enterprise User Security. No additional administration tasks are

required for provisioning and credential management. In addition, the administrative

groups for Enterprise User Security can now designate an owner, which facilitatesstronger security overall.


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Easy database registration - This feature eliminates the need for theRDBMS_SERVER_DN parameter, making configuration of enterprise users easier.

Extended and uniform audit trail - This feature improves security administration byproviding a uniform audit trail for RDBMS auditing in the form of standard and fine-

grained audit tables. Transactions and SQL information have been added to the audit

tables to further improve accountability of all users. Oracle Label Security directory integration - You can now manage Oracle Label

Security policies and user label authorizations in a central OID/LDAP repository. This

reduces administration costs and increases security by eliminating multiple managementpoints.

Authentication in DB2 does not only involve encrypting user names and passwords but also

allows for encryption of data as it travels across the network between the clients and the server.

The location of the authentication process is determined by the value of the database manager

configuration parameter AUTHENTICATION.

The following are the valid options for enabling authentication for DB2:

SERVER_ENCRYPT - This value specifies that the authentication occurs on the server.The user id and password specified during connection are encrypted and sent to the server

where they are compared with the user and password on the server side. If the match issuccessful, the user is allowed to access the database.

KRB_SERVER_ENCRYPT - This specifies that the server accepts KERBEROSauthentication or encrypted SERVER authentication schemes.

DATA_ENCRYPT - This setting specifies that the server allows for SERVERauthentication, and also that the data traveling over the network between the client and

server is encrypted.

DATA_ENCRYPT_CMP - This specifies that the server accepts encrypted SERVERauthentication schemes and the encryption of user data. This authentication type allows

for compatibility with down-level products not supporting the DATA_ENCRYPT

authentication type.

GSS_SERVER_ENCRYPT - This specifies that the server accepts GSS API-basedplug-in authentication or encrypted server authentication schemes.

To update the AUTHENTICATION instance parameter, for example to a value of

DATA_ENCRYPT, use the commands shown below:

Listing 1. Updating AUTHENTICATION instance parameter

UPDATE DBM CFG USING AUTHENTICATION DATA_ENCRYPTdb2stopdb2start

DB2 further extends security by offering a Label Based Access Control (LBAC) mechanism.The LBAC feature provides for greater granularity for controlling read and write access to


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individual rows and table columns. A new security administrator role (SECADM) has been

provided in DB2 which is needed to manipulate LBAC objects.

Users attempting to access an object must have its security label granted to them. When there's a

match, access is permitted; without a match, access is denied. There are basically three steps for

implementing LBAC security in DB2:

Create a security policy.A security policy describes the criteria that are used to decide who has access to specific

data. Only one security policy can be used to protect any one table, but different tables

can be protected by different security policies. This is done using the CREATESECURITY POLICY statement. All the management of the security policies is done

using SQL statements.

Create a security label.There are three types of security labels:

o Row security labels. A security label associated with a data row or record in adatabase table.o Column security labels. A security label associated with a column in a databasetable.

o User security labels. A security label granted to a database user.The SECADM creates security labels that are part of that policy. Once created, a security

label can be associated with individual columns and rows in a table to protect the data

held there.

Grant security labels to a users to allow them to access the data. The securityadministrator allows users access to protected data by granting them security labels.

When a user tries to access protected data, that user's security label is compared to thesecurity label protecting the data.

There are other aspects of database security beyond privileges and authorities. Briefly, here are

some of the differences and similarities between Oracle and DB2:

User authentication and authorization

Oracle uses an encrypted password stored in the dictionary once a user is created. DB2 supports

passwords for user authentication and uses the underlying operating user for authentication. Both

Oracle and DB2 support LDAP (Oracle Internet Directory and IBM Directory Server). Both

Oracle and DB2 support single sign on (SSO).

Data encryption

Oracle supports data encryption where sensitive data such as credit card numbers and some

highly sensitive business data can be encrypted. DB2 allows data encryption at the column level.

Network encryption


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Oracle provides network encryption with its Oracle Advanced Security. Oracle uses DES, 3DES

and RC4 industry standard encryptions. DB2 by itself does not enforce network encryption.However network encryption can be achieved using add-on Tivoli SecureWay.

Audit trail

Oracle allows you to audit trail users and objects. Log miner can also be used for investigatingand analyzing suspicious queries. DB2 provides a similar auditing facility. The db2audit utility

can be used for this purpose.

Back to top

XML support

In this section we compare Oracle's support forXML to DB2's. Shipped with Oracle 9i Release 2,Oracle XML DB feature provides a way to manage XML storage, retrieval and schema by

defining XMLTYPE tables and columns which are stored as CLOB or shredded (decomposed) tosmall pieces into relational tables. Oracle 10g comes with some improvements to manage XML

documents; for example, changes in schema can be dynamically reflected by mapping existing

data without the need to re-import. Oracle 10g includes toolkits such as:

XML-SQL Util (XSU) - Interface provided for PL/SQL and Java XML Developer's kits (XDK) - For supported languages such as PL/SQL, C++ and Java

Oracle 10g is still anXML-enableddatabase. All interfaces, APIs, and packages provided are to

ease the burden, complexity, and maintenance incurred to translate and map to and from XML torelational tables. XML-enabled databases, either using the CLOB or shredding methods are not

good for performance. In the case of CLOBs for example, the XML documents are stored as

image files inside the database. As you probably know, managing image files is oftencumbersome. The shredding approach is also not good for performance. After shredding an

XML document into pieces storing it in several tables, when you want to compose the XML

document back to the original, you will have to use an SQL JOIN operation. JOINs in SQL areexpensive, especially for a large number of tables. Keeping the fidelity of digital signatures can

be a challenge as well.

On the other hand, DB2 9 pureXML technology, stores XML documents natively, that is,

internally in tree format. It also allows for the use of SQL with XML extensions, Xquery andXpath to access relational and XML data. Storing XML documents natively is a better approach,

and IBM's research indicates that there is a better performance for search and retrieval of XMLdocuments, and reduction in the lines of codes for certain programs.

In order to use the pureXML feature in your database, create the database as UNICODE (forexample using codeset UTF-8). Failure to create a UNICODE database prior to creating a table

will result in an error as shown below:
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SQL1239N XML features can only be used in a Unicode database with a singledatabase partition. SQLSTATE=42997

DB2 stores relational data as in previous versions; however, XML data is stored in hierarchicalformat (as a tree using the Xquery Data Model, XDM). There is tight integration between both

XML and relational services. To store XML documents, a user needs to create a table, andspecify a column to use a new data type,XML, as shown in the example below.

Listing 2. Create a table with XML datatype

create table T (i int, doc xml)

The following diagram depicts graphically how the two columns will look:

Figure 12. DB2 storage model

As XML documents are stored in parsed hierarchical format natively in the XQuery Data Model

(XDM), there is no need for translation or mapping; the format used to store XML documents isthe format used to process it. This allows for greater performance.

Utilities such as backup, restore, import apply to tables with XML columns the same as in anyother tables. XML data can be inserted into the XML column either by using the INSERT

statement or by using the DB2 IMPORT utility (Note: DB2 LOAD utility does not support XML

yet). Prior to importing XML documents received from third parties, it is a good idea to validate

these documents against a pre-defined XML schema. To register against an XML schema, DBAs


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are required to issue theREGISTER XML SCHEMA command, ended with COMPLETE XML

SCHEMA to complete the registration process. DB2 9 also supports indexes to be created on asubset of an XML document, or on the entire document. An XPATH needs to be specified when

creating an index which would point to that particular element/attribute to be indexed.

With DB2 9 you now have four ways to access relational and XML data as shown inFigure 13:

Plain SQL (no XQuery involved) SQL/XML, that is, XQuery embedded in SQL XQuery as a stand-alone language (no SQL involved) Xquery with embedded SQL

Figure 13. PureXML Query possibilities

Table 3 compares the XML capabilities between DB2 9 and Oracle 10g.

Table 3. XML Feature Comparisons

XML capabilitiesOracle

10g IBM DB2 9 for Linux, Unix and Windows

XML-enabled store Not ApplicableXML native store Ease of maintenance for big

environment

Highly scalable Store XML documents as

CLOBs

To move forward however, XML nativestorage is encouraged.

Shredding To move forward however, XML nativestorage is encouraged.

There are more developerWorks articles on IBM pureXML capabilities such asQuery DB2

XML data with XQuery,Query DB2 XML Data with SQLamongst others for more in-depthdiscussions.

Back to top
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Partitioning

DB2's table partitioning (a.k.a Range partitioning), is similar to Oracle's partitioning. It basically

allows a single logical table to be broken up into multiple physical storage objects across one or

more table spaces. Each of the objects would correspond to a 'partition' and would allow each

table space to contain a range of data which can be accessed very easily.

In DB2 there are several ways to partition your data, and you can apply these methods

simultaneously on the same data. To avoid confusion, here is a short explanation about the

different ways to provide this partitioning:

DATABASE PARTITIONING - distributing data by key hash across logical nodes of thedatabase (DPF).

RANGE/TABLE PARTITIONING (Available with DB2 9) - splitting data by key rangeover multiple physical objects within a logical database partition.

MULTI DIMENSIONAL CLUSTERING (MDC) - organizing data in table (or range of atable) by multiple key values.

With Table partitioning, new in DB2 9, table data can be divided based on particular values in

one or more table columns across different table spaces. These partitions can be backed up andrestored individually, and improve performance of certain queries, as the DB2 optimizer is aware

of the existence of these partitions and can eliminate scanning of data partitions not required inthe query. For example, if you had partition your table in four quarters of the year, and yourquery only needs data from the 4th quarter, DB2 would skip parsing the first three quarters and

would go straight to the fourth quarter and parse it. This is called partition elimination.

As mentioned before, it is important to note that all 3 methods of data organization i.e. Database

Partitioning, Table Partitioning and Multi Dimensional Clustering can be used simultaneously inDB2 9.

The following example creates a table customer where rows with l_shipdate >= '01/01/2006' and

l_shipdate = '04/01/2006' andl_shipdate


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Compression

There are two compression features provided by Oracle; index and table level compression.

Improper planning of these features may have adverse effect in performance.

Oracle introduced index compression since version 8i. Indexes that can be compressed arebitmap, btree and index organized tables. To use index compression is straightforward; forexample, to create an index with the compression feature, use

Listing 4. Create index with compression

CREATE INDEX ord_customer_ix_demoON orders (customer_id, sales_rep_id)COMPRESS 1;

For indexes that were not created initially with compression, you can turn them to compression

by altering them. The following shows a sample how index can be altered to includecompression.

Listing 5. Alter index with compression

alter index ord_customer_ix_demo rebuild compress

Currently, Oracle doesn't provide any automated advisor to pinpoint which indexes should be

compressed. Most of the benefits gained by index compression requires proper planning by

seasoned DBAs who with intimate knowledge of Oracle CBO.

Table compression on the other hand, was introduced in Oracle 9i release 2. It can be used to

compress entire tables, table partitions, and materialized views. The compression can be appliedto all partitions or some partitions. Though table compression works for a non-partitioned table,

its usage for non-partitioned tables in OLTP workloads may not be desirable as insert and update

performance may suffer. In Oracle table compression, duplicate values are removed in a database

block, and information is stored to recreate the uncompressed data within the block. Thefollowing example shows how to create partition table with compression.

Listing 6. Create table with compression

CREATE TABLE costs_demo (prod_id NUMBER(6), time_id DATE,unit_cost NUMBER(10,2), unit_price NUMBER(10,2))

PARTITION BY RANGE (time_id)(PARTITION costs_old

VALUES LESS THAN (TO_DATE('01-JAN-2003', 'DD-MON-YYYY')) COMPRESS,

PARTITION costs_q1_2003VALUES LESS THAN (TO_DATE('01-APR-2003', 'DD-MON-

YYYY')),PARTITION costs_q2_2003

VALUES LESS THAN (TO_DATE('01-JUN-2003', 'DD-MON-
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YYYY')),PARTITION costs_recent VALUES LESS THAN (MAXVALUE));

To turn a table into a compressed table, use alter table move compress. A

compressed table, however, does not allow adding or dropping of columns.

With respect to DB2, there were several compression methods prior to DB2 9, however, it iswith DB2 9 that row compression is introduced. Row compression requires the creation of a

dictionary which stores a mapping between repetitive patterns or entries and numeric keys. The

compression algorithm is intelligent enough not to compress rows that will not realize in any

significant disk-space saving.

DB2's row compression, unlike Oracle's key compression, does not require keys to be specified.

Compression is enabled at individual table level via the CREATE TABLE or ALTER TABLE

commands. For example:

Listing 7. Create/Alter table with COMPRESSION YES

CREATE TABLE Sales COMPRESS YESALTER TABLE Sales COMPRESS YES

To achieve the same effect using the DB2 Control Center, during the column definition (second

step in the table creation wizard), ensure that you choose the checkbox, Store table data in a

compressed formatlocated at the bottom of the panel (as the following diagram shows).

Figure 14. DB2 Control Center - Creating table with compression

The table dictionary is built only when a REORG is performed, after which the data in the tablecan be compressed. The dictionary gets updated for every subsequent REORG operation. The

compressed data is kept both on disk and memory and DB2 also compresses user data stored in

log files, thereby reducing log file size.

Note that each partition of a partitioned table can have a different compression dictionaries andeach partition of a table in DPF can have a different compression dictionaries.

Besides, data row compression, other compression mechanisms offered by DB2 9 include:
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NULL and Default Value Compression (V8 GA): Compression for null, zero length datain variable length columns and system default value.

Multidimensional Clustering (V8 GA): Implements a form of index compression byusing block indexes, one index entry for thousands of records.

Database Backup Compression (V8 FP4): Compression to result in smaller backupimages.

XML Parsing

Back to top

Autonomic

Going from Oracle 9i to 10g, there are few tuning improvements provided by Oracle. Oracle

automated the following tuning areas:

Redo Logfile Sizing Advisor - This feature recommends the optimal size of redo log filesin order to avoid excessive disk I/Os due to frequent checkpointing.

Automatic Checkpoint Tuning - The Oracle Database can now self-tune checkpointing toachieve good recovery times with low impact on normal throughput. You no longer have

to set any checkpoint-related parameters.

Automatic Shared Memory Tuning - Automatic Shared Memory Tuning automates theconfiguration of System Global Area (SGA) memory-related parameters (buffer cache,

shared pool) through self-tuning algorithms. It simplifies database configuration, ensures

most efficient utilization of available memory and improves performance.

Transaction Rollback and Recovery Monitoring - This feature enables you estimate howlong it will take to roll back a transaction. You can also monitor the progress oftransactions being recovered and estimate the average speed of transaction recovery.

Oracle also provides some advisors such as segment and undo advisors. The segment advisor is

based on the level of space fragmentation within an object, and as result, gives advice on whetheran object is a good candidate for the new online shrink operation. As well, this advisor give

reports on the historical growth trend of segments, and proved to be especially informative for

capacity planning. Undo Advisor, on the other hand, helps administrators to make the right

judgement in sizing the undo table space in both flash back and non-flashback features. It advisesadministrators in setting UNDO_RETENTION appropriately to avoid the age-old 'snapshot too

old' problem.

DB2 9 introduces several new autonomic enhancements. For example, DB2 9 introduces a new

self-tuning memory feature (using the self_tuning_mem database configuration parameter) that

simplifies the task of memory configuration by automatically setting values for several memory

configuration parameters. When enabled, the automatic tuner acting as dispatcher, will figure outthe memory resources available and distribute them to several memory consumers for the

database dynamically.
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Other than the self tuning memory, DB2 9 introduces other enhancements as seen below. It is a

non-exhaustive but important list.

Automatic configuration

Version 8 of DB2 introduced the Configuration Advisor that detected the system and databasecharacteristics - CPUs, memory, database size, number of tables, etc. and recommended valuesfor configuration parameters. DB2 9 goes even further - it runs the configuration advisor

automatically after you create a database, and makes some basic tuning decisions by default. For

example it configures the size of the default buffer pool, I/O cleaners and I/O servers, etc. This

initial automatic tuning means that your database will have better performance than a databasecreated with the previous database configuration default values, enabling better out-of-the-box

operation.

Automatic data statistics collection

DB2 9 also enables automation of certain ongoing tasks by default. With this feature, DB2determines which statistics are required and need to be updated and then automatically executes

the RUNSTATS utility in the background.

Automatic storage management

DB2 9 extends the automated storage features first introduced in DB2 V8.2.2. Automatic storage

automatically grows the size of your database across disk and file systems and since it

automatically grows the size of the database, it removes the need to managing storage containers

by DBAs. When you create databases in DB2 9, the automatic storage management feature isenabled by default.

Automatic table and index reorganization enhancements

Automatic reorg was introduced since version 8.2. However, DB9 brings it further to allow youto do the following

Specify the use of a system temporary table space with an appropriate pagesize for anoffline table reorganization.

Tables to be reorg-ed can be limited in size. Specify that automatic index reorganizations should be run online and in the online

maintenance window.

Specify whether to keep or rebuild compression dictionaries during reorganization.

Back to top

Tools
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We shall look at tools from different areas such as database creation and maintenance, network,

administration GUI, performance tuning, data movement and backup-recovery tools.Figure 15shows the DB2 9 GUI tools.

Figure 15. DB2 9 GUI Tools

Let's take a look at how similar tasks are performed in Oracle and DB2 9.

Database Creation and Maintenance

Oracle provides the Database Configuration Assistant (dbca) as the GUI tool to create databases.

For database maintenance, Oracle provides the Oracle Enterprise Manager. DB2 databases can

be created and maintained from the DB2 Control Center.

Network

Oracle provides the Network Configuration Assistant (netca) for network configuration.

Alternatively, you can use the Oracle Network Manager to configure service naming, listener,

profile and Oracle name servers. DB2 uses the CATALOG command to catalog nodes and

databases. Cataloging can also be done using either the DB2 command line or DB2Configuration Assistant GUI.

Administration

The Oracle Enterprise Manager provides a wide range of administrative capabilities for the day-to-day tasks of administrators. DB2 Control Center provides similar functions as Oracle

Enterprise Manager. Apart from the DB2 Control Center, the DB2 command line processor can


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also be used to issue DDL and DML statements. This utility is similar to the Oracle SQLPLUS

utility.Figure 16shows the DB2 command line processor.

Figure 16. DB2 Command Line Processor

Commands can also be issued from the Command Center, shown inFigure 17.
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Figure 17. Command Center GUI (GUI version of DB2 Command Line Processor)

Performance tuning

Oracle Enterprise Manager comes with Change Management pack, Tuning Pack, and Diagnostic

Pack. DB2 provides the Event Analyzer, Health Center, Indoubt Transaction Manager and

Memory Visualizer as GUI tools for performance tuning tasks.

Data movement

Oracle provides SQL Loader (sqlldr) for loading data in delimited text format. Import (imp) and

export (exp) can be used to perform logical import and export. DB2 provides similar import,

export and load utilities . For cross platform data movement, DB2 provides the db2move utility.

Backup and Recovery

Oracle provides Recovery Manager as an option for hot backup. Backing up databases in DB2

can be accomplished using the backup command or the DB2 Control Center.


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Oracle 10g Enteprise Manager comes with new performance overview charts. The enhanced

Oracle Enterprise Manager HTML interface provides a central point of access to all databaseperformance-related statistics and facilitates complete monitoring and diagnostics.

Apart from interfaces that were shipped with DB2 UDB version 8, DB2 9 introduces a new no-

charge application development tool, based on the Eclipse framework called tbe DB2 DeveloperWorkbench (DWB). This tool, which comes as a separate download or CD, replaces DB2

version 8's Development Center. The DWB is a one-stop center for creating, editing, debugging,deploying, and testing DB2 stored procedures and user-defined functions. You can also use the

DWB to develop SQLJ applications, and create, edit, and run SQL statements and XML queries.

The DWB has several views for developing DB2 business objects, such as:

Database Explorer view - Shows what's in the database (tables, stored procedures, userdefined functions, dependencies, remote servers, etc) and allows you to perform actions

on these objects.

Data Project Explorer view - Lets you perform development actions for procedures, userdefined functions, and SQL statements, with easy operations such as drag & drop, copy

& paste, wizards, context sensitive completion options, etc.

Data Output view - Lets you see reports of data development actions against a database.Other than the functionality of DB2 version 8's Development Center, the new DeveloperWorkbench includes support for migrating projects, comparing routines, XML functions andbuilding XQueries using the XQuery Builder, etc. You can download theDB2 Developer

Workbenchfrom the partner web site.

For more details about the DB2 Developer Workbench review this tutorialtutorialin

developerWorks. For more exhaustive examples and features, refer to theApplicationdevelopment enhancementsarticle in developerWorks.

Figure 18 shows how DWB can be used to create stored procedures:
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Figure 18. DB2 Developer WorkBench

Back to top

Summary

In this article we've introduced you to DB2 9 for Linux, UNIX and Windows by using yourcurrent knowledge of Oracle 10g Release 2 as leverage. We briefly described the DB2 9

architecture, background processes, memory model, security, tools, and so on. There are many

similarities between Oracle and DB2 9, and we have pointed out some of the differences so you

can use your current knowledge to become successful with DB2 9.

Table 3summarizes the differences and similarities between Oracle and DB2 9 that we'vediscussed.

Table 3 - Summary of Oracle vs. DB2 9 concepts

Oracle DB2 9 Comment

Instance Instance A DB2 instance can contain several databasesDatabase Database

initSID.ora

OR SPFILE

DBM CFG andDB

CFG

DB2 uses two levels of configuration:- Database Manager

Configuration (DBM CFG) (at the instance level)- Database

Configuration (DB CFG) (at the database level).Like inOracle, many of these configuration parameters can be

dynamically changed.

Table spaces Table spacesDB2 supports SMS and DMS Table spaces. DMS Tablespaces are similar to Oracle's.

Data Blocks Pages

DB2 supports these page sizes: 4k, 8k, 16k, 32k. A row

must fit any of these page sizes. It cannot span to otherpages like in Oracle's.
http://www.ibm.com/developerworks/data/library/techarticle/dm-0401gupta/?ca=dgr-lnxw06Oracle2DB2#ibm-pconhttp://www.ibm.com/developerworks/data/library/techarticle/dm-0401gupta/?ca=dgr-lnxw06Oracle2DB2#ibm-pconhttp://www.ibm.com/developerworks/data/library/techarticle/dm-0401gupta/?ca=dgr-lnxw06Oracle2DB2#table3http://www.ibm.com/developerworks/data/library/techarticle/dm-0401gupta/?ca=dgr-lnxw06Oracle2DB2#table3http://www.ibm.com/developerworks/data/library/techarticle/dm-0401gupta/?ca=dgr-lnxw06Oracle2DB2#table3http://www.ibm.com/developerworks/data/library/techarticle/dm-0401gupta/?ca=dgr-lnxw06Oracle2DB2#ibm-pcon


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Extents Extents

Data FilesDMS Table spacecontainers

Containers for DMS table spaces can be raw devices orfiles.

Redo Log

FilesTransaction Log Files

Data Buffers Buffer pools.DB2 does not have a predefined set of bufferpools, but youcan create as many as desired. A bufferpool of a given page

size must be exist prior to creating a table space with the

given page size.

SGA

Database Manager and

Database Shared

memoryData

DictionaryCatalog

Library

cachePackage cache

Large Pool Utility HeapData

DictionaryCache

Catalog cache

SYSTEM

table space

SYSCATSPACE table

space

Resources

ibm db2 using oracle skills

Documents