Tài liệu OCA: Oracle Database 11g Administrator Certified Associate- P10 pptx

You will learn what con-stitutes the Oracle Database 11g—an overview of the memory structures, the processes that manage the database, and how data is stored in the database.. As the DB

5 You create a view based on the EMPLOYEES table using the following SQL.

CREATE VIEW MYVIEW AS SELECT * FROM EMPLOYEES;

You modify the table to add a column named EMP_SSN What do you need to do to have this

new column appear in the view?

A Nothing Since the view definition is selecting all columns, the new column will appear

in the view automatically

B Recompile the view using ALTER VIEW MYVIEW RECOMPILE.

C Re-create the view using CREATE OR REPLACE VIEW.

D Add the column to the view using ALTER VIEW MYVIEW ADD EMP_SSN.

6 Which is a valid status of a constraint created on a view?

A DISABLE VALIDATE

B DISABLE NOVALIDATE

C ENABLE NOVALIDATE

D All of the above

7 The SALARY column of the EMPLOYEE table is defined as NUMBER(8,2), and the

COMMIS-SION_PCT column is defined as NUMBER(2,2) A view is created with the following code:

CREATE VIEW EMP_COMM ASSELECT LAST_NAME,SALARY * NVL(COMMISSION_PCT,0) CommissionFROM EMPLOYEES;

What is the datatype of the COMMISSION column in the view?

382 Chapter 7 N Creating Schema Objects

9 The EMPLOYEE table has the following columns:

EMP_ID NUMBER (4)EMP_NAME VARCHAR2 (30)SALARY NUMBER (6,2)DEPT_ID VARCHAR2 (2)Which query will show the top five highest-paid employees?

10 The EMPLOYEE table has the following columns:

EMP_ID NUMBER (4) PRIMARY KEYEMP_NAME VARCHAR2 (30)

SALARY NUMBER (6,2)DEPT_ID VARCHAR2 (2)

A view is defined using the following SQL:

CREATE VIEW EMP_IN_DEPT10 ASSELECT * FROM EMPLOYEEWHERE DEPT_ID = ‘HR’;

Which INSERT statement will succeed through the view?

A INSERT INTO EMP_IN_DEPT10 VALUES (1000, ‘JOHN’,1500,’HR’);

B INSERT INTO EMP_IN_DEPT10 VALUES (1001, NULL,1700,’AM’);

C INSERT INTO EMP_IN_DEPT10 VALUES (1002, ‘BILL’,2500,’AC’);

D All of the above

11 To be able to modify a join view, the view definition should not contain which of the

fol-lowing in the top-level query? (Choose all that apply.)

A create sequence desc_seq start with 0 increment by -1 maxvalue 1;

B create sequence desc_seq increment by -1;

C create sequence desc_seq start with 0 increment by -1;

D Sequences can only increase.

13 Which statement is most correct in describing what happens to a synonym when the

under-lying object is dropped?

A The synonym’s status is changed to INVALID.

B You can’t drop the underlying object if a synonym exists unless the CASCADE clause is

used in the DROP statement

C The synonym is automatically dropped with the underlying object.

D Nothing happens to the synonym.

384 Chapter 7 N Creating Schema Objects

14 There is a public synonym named PLAN_TABLE for SYSTEM.PLAN_TABLE Which of the

fol-lowing statements will remove this public synonym from the database?

A drop table system.plan_table;

B drop synonym plan_table;

C drop table system.plan_table cascade;

D drop public synonym plan_table;

15 A developer reports that she is receiving the following error:

SELECT key_seq.currval FROM dual;

ERROR at line 1:

ORA-08002: sequence KEY_SEQ.CURRVAL is not yet definedWhich of the following statements does the developer need to run to fix this condition?

A create sequence key_seq;

B create synonym key_seq;

C select key_seq.nextval from dual;

D grant create sequence to public;

16 Bitmapped indexes are best suited to which type of environment?

A High-cardinality columns

B Online transaction processing (OLTP) applications

C Full-table scan access

D Low- to medium-cardinality columns

17 Which clauses in a SELECT statement can an index be used for? (Choose all that apply.)

A SELECT

B FROM

C WHERE

D HAVING

18 You need to generate artificial keys for each row inserted into the PRODUCTS table You

want the first row to use a sequence value of 1000, and you want to make sure that no sequence value is skipped Which of the following statements will meet these requirements?

A CREATE SEQUENCE product_key2

START WITH 1000 INCREMENT BY 1 NOCACHE;

B CREATE SEQUENCE product_key2

START WITH 1000 NOCACHE;

C CREATE SEQUENCE product_key2

START WITH 1000 NEXTVAL 1 NOCACHE;

D Options A and B meet the requirements.

E None of the above statements meet all the requirements.

19 Which statement will display the last number generated from the EMP_SEQ sequence?

A select emp_seq.curr_val from dual;

B select emp_seq.currval from dual;

C select emp_seq.lastval from dual;

D select last_number from all_sequences where sequence_name =’EMP_SEQ’;

E You cannot get the last sequence number generated.

20 Which statement will create a sequence that will rotate through 100 values in a round-robin

manner?

A create sequence roundrobin cycle maxvalue 100;

B create sequence roundrobin cycle to 100;

C create sequence max_value 100 roundrobin cycle;

D create rotating sequence roundrobin min 1 max 100;

386 Chapter 7 N Creating Schema Objects

Answers to Review Questions

1 B A view is dropped using the DROP VIEW view_name; command.

2 A You can perform an INSERT, UPDATE, or DELETE operation on the columns involving

only one base table at a time There are also some restrictions on the DML operations you perform on a join view

3 D Since the view definition includes a DISTINCT clause, only queries are allowed on the

view

4 B, E The OR REPLACE option in the CREATE VIEW statement is used to modify the

defini-tion of the view The FORCE opdefini-tion can be used to create the view with errors The ALTER VIEW statement is used to compile a view or to add or modify constraints on the view

5 C When you modify the base table, the view becomes invalid Oracle will recompile the

view the first time it is accessed Recompiling the view will make it valid, but the new umn will not be available in the view This is because when you create the view using *, Oracle expands the column names and stores the column names in the dictionary

col-6 B Since the constraints on the view are not enforced by Oracle, the only valid status of a

constraint can be DISABLE NOVALIDATE You must specify this status when creating straints on a view

con-7 C When numeric operations are performed using numeric datatypes in the view definition,

the resulting column will be a floating datatype, which is NUMBER without any precision

or scale

8 D The FOR UPDATE OF clause is not supported in the view definition The FOR UPDATE

clause locks the rows, so it is not allowed

9 C You can find the top five salaries using an inline view with the ORDER BY clause The

Oracle 11g Optimizer understands the top-n rows query Option B would have been correct

if you had ROWNUM <= 5 in the WHERE clause

10 D The view is based on a single table, and the only constraint on the table is the primary

key Although the view is defined with a WHERE clause, you have not enforced that check while using DML statements through the WITH CHECK OPTION clause

11 A, C, E, F To be able to update a base table using the view, the view definition should not

have a DISTINCT clause, a GROUP BY clause, a START WITH clause, a CONNECT BY clause, ROWNUM, set operators (UNION, UNION ALL, INTERSECT, or MINUS), or a subquery in the SELECT clause

12 A For a descending sequence, the default START WITH value is –1, and the default MAXVALUE

value is –1 To start the sequence with 0, you must explicitly override both of these defaults

13 A When the underlying object is dropped, the synonym will become INVALID You can see

the status of the synonym by querying the USER_OBJECTS dictionary view

14 D To remove a public synonym, use the DROP PUBLIC SYNONYM statement The DROP

TABLE statement will remove a table from the database but will not drop any synonyms on the table The synonym will become invalid

15 C A sequence is not yet initialized if NEXTVAL has not yet been selected from it within the

current session It has nothing to do with creating a sequence, creating a synonym, or ing privileges

grant-16 D Bitmapped indexes are not suited for high-cardinality columns (those with highly

selec-tive data) OLTP applications tend to need row-level locking, which is not available with bitmap indexes Full-table scans do not use indexes Bitmap indexes are best suited to multiple combinations of low- to medium-cardinality columns

17 A, C The obvious answer is C, but an index also can be used for the SELECT clause If an

index contains all the columns needed to satisfy the query, the table does not need to be accessed

18 D Both options A and B produce identical results, because the INCREMENT BY 1 clause is

the default if it is not specified Option C is invalid because NEXTVAL is not a valid keyword within a CREATE SEQUENCE statement

19 B Option D is close, but it shows the greatest number in the cache, not the latest generated

The correct answer is from the sequence itself, using the pseudocolumn CURRVAL

20 A The keyword CYCLE will cause the sequence to wrap and reuse numbers The keyword

MAXVALUE will set the largest value the sequence will cycle to The name roundrobin is there to confuse to you

Database 11g:

Administration I

8 Database 11g

Components and Architecture

Explain the Memory Structures Û

N Describe the Process Structures Û

N Overview of Storage Structures Û

N

Preparing the Database Environment

ÛÛ

Identify the tools for Administering an Oracle Database Û

N Plan an Oracle Database installation Û

N Install the Oracle software by using Oracle Universal Û

N Installer (OUI)

With this chapter, you’ll start learning Oracle Database 11g (Oracle 11g) database administration This chapter and the

remaining chapters of the book will discuss the objectives for

the Oracle 11g Administration I OCA certification exam.

With the release of Oracle 11g, Oracle Corporation has delivered a powerful and

feature-rich database that can meet the performance, availability, recoverability, application-testing, and security requirements of any mission-critical application As the Oracle DBA, you are

responsible for managing and maintaining the Oracle Database 11g throughout its life

cycle, from initial installation, creation, and configuration to final deployment ing these tasks requires a solid understanding of Oracle’s product offerings so that you can apply the proper tools and features to the application You must also use relational database concepts to design, implement, and maintain the tables that store the application data At the heart of these activities is the need for a thorough understanding of the Oracle architecture and the tools and techniques used to monitor and manage the components of this architecture

Perform-I will begin the chapter by reviewing the Oracle Database basics You will learn what

con-stitutes the Oracle Database 11g—an overview of the memory structures, the processes that

manage the database, and how data is stored in the database I will also discuss the tools used

to administer the Oracle Database 11g and how to install the Oracle 11g software.

Exam objectives are subject to change at any time without prior notice and at Oracle’s sole discretion Please visit Oracle’s Training and Certifica-

db_pages.getpage?page_id=41&p_exam_id=1Z0_052 for the most current exam-objectives listing.

Oracle Database Fundamentals

Databases store data The data itself is composed of related logical units of information

The database management system (DBMS) facilitates the storage, modification, and

retrieval of this data Some early database technologies used flat files or hierarchical file structures to store application data Others used networks of connections between sets

of data to store and locate information The early DBMS architecture mixed the physical manipulation of data with its logical manipulation When the location of data changed, the

application referencing the data had to be updated Relational databases brought a tionary change to this architecture Relational DBMS introduced data independence, which separated the physical model of the data from its logical model Oracle is a relational DBMS

revolu-All releases of Oracle’s database products have used a relational DBMS model to store data in the database This relational model is based on the groundbreaking work of Dr

Edgar Codd, which was first published in 1970 in his paper “A Relational Model of Data for Large Shared Data Banks.” IBM Corporation, which was then an early adopter of Dr

Codd’s model, helped develop the computer language that is used to access all relational databases today—Structured Query Language (SQL) The great thing about SQL is that you can use it to easily interact with relational databases without having to write complex computer programs and without needing to know where or how the data is physically stored on disk You saw several SQL statements in the previous chapters

Relational Databases

The concept of a relational database management system (RDBMS) is that the data

con-sists of a set of relational objects The basic storage of data in a database is a table The relations are implemented in tables, where data is stored in rows and columns Figure 8.1 shows such a relationship

F I g u r e 8 1 Relational tables

EMP (Employee Table) EMPNO

7369 7499 7521 7566 7654 7698 7844

ENAME SMITH ALLEN WARD JONES MARTIN BLAKE URNER

JOB CLERK SALESMAN SALESMAN MANAGER SALESMAN MANAGER SALESMAN

MGR 7902 7698 7698 7839 7698 7839 7698

HIREDATE 17-DEC -8 20-FEB-8 22-FEB-8 02-APR-8 28-SEP-8 07-MAY-8 08-SEP-8

0800 11600 11250 12975 11250 12850 11500

20 30 30 20 30 30 30

300 500 1400

Primary Key Column

Primary Key Column

Foreign Key Column DEPT (Department Table)

DNAME ACCOUNTING RESEARCH SALES OPERATIONS

DEPTNO 10 20 30 40

LOC NEW YORK DALLAS CHICAGO BOSTON

SAL

394 Chapter 8 N Introducing Oracle Database 11g Components and Architecture

The DEPT table in the lower part of the figure stores information about departments

in the company Each department is identified by the department ID Along with the ID, the name and location of the department are also stored in the table The EMP table stores information about the employees in the company Each employee is identified by a unique employee ID This table includes employee information such as hire date, salary, manager, and so on The DEPTNO column in both tables then provides a relationship between the tables A department may have many employees, but an employee can work for only one department

Since the user accessing this data doesn’t need to know how or where the row is stored

in the database, there must be a way to uniquely identify the rows in the tables In our example, the department is uniquely identified by department number, and an employee is identified by an employee ID The column (or set of columns) that uniquely identifies a row

is known as the primary key According to relational theory, each table in a relational

data-base must have a primary key

When relating tables together, the primary key of one table is placed in another table

For example, the primary key of the DEPT table is a column in the EMP table In RDBMS

terminology, this is known as a foreign key A foreign key states that the data value in the

column exists in another table and should continue to exist in the other table to keep the relationship between tables The table where the column is a primary key is known as the

parent table, and the table where the foreign key column exists is known as the child table

Oracle enforces the parent-child relationship between tables using constraints.

Oracle Database 11g Objects

Every RDBMS supports a variety of database objects Oracle 11g supports the entire set of

database objects required for a relational database, such as tables, views, constraints, and

so on It also supports a wide range of objects specific to the Oracle Database 11g, such as

packages, sequences, materialized views, and so on Table 8.1 lists the objects available in

Oracle 11g I also discussed many of these in Chapter 6, “Creating Tables and Constraints,”

and Chapter 7, “Creating Schema Objects.”

tA b l e 8 1 Oracle Database 11g Objects

Object Type Description

stores rows of data.

similar to views but take up storage space to store data.

Object Type Description

Index-organized

numbers.

occurs.

user-defined functions to return a value.

You use SQL to create database objects and to interact with application data In the next

section, I will discuss the tools available to access and administer Oracle 11g database.

Interacting with Oracle 11g

SQL is the language used to interact with the Oracle 11g database Many tools are available for the DBA to administer an Oracle 11g database The common tools are as follows:

SQL*Plus, which is a command-line interface utility

Û N

SQL Developer, a GUI tool

Û N

Oracle Enterprise Manager Database Control, a GUI tool

Û N

tA b l e 8 1 Oracle Database 11g Objects (continued)

396 Chapter 8 N Introducing Oracle Database 11g Components and Architecture

Using SQL*Plus and SQL Developer, you interact directly with the Oracle 11g database

using SQL statements and a superset of commands such as STARTUP, SHUTDOWN, and so on

Using Enterprise Manager, you interact indirectly with the Oracle 11g database.

SQL*Plus

SQL*Plus is the primary tool for an Oracle DBA to administer the database using SQL

commands Before you can run SQL statements, you must connect to the Oracle 11g

data-base You can start SQL*Plus from a Windows command prompt using the SQLPLUS.EXE

executable or using the $ORACLE_HOME/bin/sqlplus executable on the Unix/Linux form Figure 8.2 shows connecting to SQL*Plus from a Linux workstation

plat-F I g u r e 8 2 SQL*Plus login in Linux

To get an overview of SQL*Plus and how to connect to the database using SQL*Plus, please refer to Chapter 1, “Introducing SQL.”

SQL Developer

SQL Developer is a free GUI database-development tool With SQL Developer, you can create and view the database objects, make changes to the objects, run SQL statements, run PL/SQL programs, create and edit PL/SQL programs, and perform PL/SQL debugging

SQL Developer also includes a migration utility to migrate Microsoft Access and Microsoft

SQL Server databases to Oracle 11g Figure 8.3 shows the object browser screen of SQL

Enterprise Manager Database Control

Oracle Enterprise Manager Database Control is a web-based database management tool

that is bundled with the Oracle 11g database This is a graphical tool specifically designed

to administer the Oracle database The Enterprise Manager Database Control is used to age a single database, whereas the Enterprise Manager Grid Control can manage multiple databases and other services and applications, such as OAS, and even non-Oracle applica-tions at the same time Figure 8.4 shows the Enterprise Manager Database Control home screen, where an overview of the database is shown

man-398 Chapter 8 N Introducing Oracle Database 11g Components and Architecture

F I g u r e 8 4 Enterprise Manager home screen

For all the database-administration examples in this chapter, you may use either SQL*Plus

to perform the SQL command line or use the GUI tool Enterprise Manager (EM) Database

Control Before learning to administer the Oracle 11g database, let’s start with the basics

In the next section, you’ll learn about Oracle 11g architecture.

Oracle 11g Architecture

Each database-administration and -development tool described previously allows a user

to interact with the database Using these tools requires that user accounts be created in the database and that connectivity to the database be in place across the network Users must also have adequate storage capacity for the data they insert, and they need recovery mechanisms for restoring the transactions they are performing in the event of a hardware

failure As the DBA, you take care of each of these tasks, as well as others, which include the following:

Selecting the server hardware on which the database software will run

Û N

Installing and configuring the Oracle 11

Û

Creating the Oracle 11

Û

Creating and managing the tables and other objects used to manage the application data

Û N

Creating and managing database users

Û N

Establishing reliable backup and recovery processes for the database

Û N

Monitoring and tuning database performance

Û N

The remainder of this book is dedicated to helping you understand how to perform these and other important Oracle database-administration tasks But first, to succeed as an Oracle DBA, you need to completely understand Oracle’s underlying architecture and its mechanisms

Understanding the relationship between Oracle’s memory structures, background processes, and I/O activities is critical before learning how to manage these areas

The Oracle server architecture can be described in three categories:

User-related processes

Û N

Logical memory structures that are collectively called an

data-Database is a confusing term that is often used to represent different things on different

platforms; the only commonality is that it is something related to storing data In Oracle,

however, the term database represents the physical files that store data An instance is

com-posed of the memory structures and background processes Each database should have at least one instance associated with it It is possible for multiple instances to access a single

database; such a configuration is known as Real Application Clusters (RAC) In this book,

however, you’ll concentrate only on single-instance databases because RAC is not part of the certification exam

Figure 8.5 shows all the parts of an Oracle instance and database

Although the architecture in Figure 8.5 may at first seem complex, each of these tecture components is described in more detail in the following sections, beginning with the user-related processes, and is actually fairly simple This figure is an important piece of

archi-fundamental information when learning about the Oracle 11g architecture.

The key database components are memory structures, process structures, and storage structures Process and memory structures together are called

an instance; the storage structure is called a database Taken together, the instance and the database are called an Oracle server.

400 Chapter 8 N Introducing Oracle Database 11g Components and Architecture

F I g u r e 8 5 The Oracle 11g architecture

Server

Tablespace 1

SGA

Server Process 2

Background Processes

PGA

Instance

Physical Database Structure

Database Data

Database

Archive Log Files Password Files Parameter Files

Logical Database Structure

SYSTEM

User Processes

At the user level, two types of processes allow a user to interact with the instance and,

ulti-mately, with the database: the user process and the server process

Whenever a user runs an application, such as a human-resources or order-taking tion, Oracle starts a user process to support the user’s connection to the instance Depending

applica-on the technical architecture of the applicatiapplica-on, the user process exists either applica-on the user’s own computer or on the middle-tier application server The user process then initiates a con-nection to the instance Oracle calls the process of initiating and maintaining communication

between the user process and the instance a connection Once the connection is made, the user establishes a session in the instance.

After establishing a session, each user starts a server process on the host server itself

It is this server process that is responsible for performing the tasks that actually allow the user to interact with the database

Examples of these interactions include sending SQL statements to the database, retrieving needed data from the database’s physical files, and returning that data to the user.

Server processes generally have a one-to-one relationship with user processes—in other words, each user process connects to one and only one server process However, in some Oracle configurations, multiple user processes can share a single server process We will discuss Oracle connection configurations in Chapter 11, “Understanding Network Architecture.”

In addition to the user and server processes that are associated with each user

connec-tion, an additional memory structure called the program global area (PGA) is also created

for each user The PGA stores user-specific session information such as bind variables and session variables Every server process on the server has a PGA memory area Figure 8.6 shows the relationship between a user process, server processes, and the PGA

F I g u r e 8 6 The relationship between user and server processes and the PGA

User Process

The user process communicates with the server process on the host server using the PGA to store session-specific information.

The user starts the Oracle-based application on their computer, creating a user process.

Host Server

PGA Oracle Instance Session

Server Process

PGA memory is not shared Each server process has a PGA associated with it and is exclusive As a DBA, you set the total memory that can be allocated to all the PGA memory allocated to all server and background processes

The server process communicates with the Oracle instance on behalf of the user The Oracle instance is examined in the next section

402 Chapter 8 N Introducing Oracle Database 11g Components and Architecture

The Oracle Instance

An Oracle database instance consists of Oracle’s main memory structure, called the system

global area (SGA), and several Oracle background processes It is with the SGA that the

server process communicates when the user accesses the data in the database Figure 8.7 shows the components of the SGA

F I g u r e 8 7 SGA components

Background Processes

SGA

Redo Buffer Large Pool Java Pool Streams Pool

Data Dictionary Cache

Result Cache

Control Structures

Shared SQL Area

Shared PL/SQL Area Library Cache

The components of the instance are described in the following sections

Oracle Memory Structures

The SGA is a shared memory area All the users of the database share the information maintained in this area Oracle allocates memory for the SGA when the instance is started and deallocates it when the instance is shut down The SGA consists of three required com-ponents and four optional components Table 8.2 describes the required components

tA b l e 8 2 Required SGA Components

SGA Component Description

issued by database users Database buffer cache Caches the data that has been most recently accessed by data-

base users

Table 8.3 describes the optional components

tA b l e 8 3 Optional SGA Components

SGA Component Description

when Oracle’s JVM option is used.

backup and restore activities and Shared Server components.

Oracle’s Advanced Queuing option is used.

results of SQL queries and PL/SQL functions for better performance.

Oracle 11g can manage the components of the SGA dynamically, without exceeding the

value specified by the DBA for the parameter SGA_MAX_SIZE, but only for ASSM Memory in

the SGA is allocated in units of contiguous memory called granules The size of a granule

depends on the parameter MEMORY_MAX_TARGET If MEMORY_MAX_TARGET is larger than 1024MB, the granule size is either 16MB or 4MB MEMORY_MAX_TARGET is discussed in detail in Chap-ter 14, “Maintaining the Database and Managing Performance.” A minimum of three granules must be allocated to SGA—one each for the required components in Table 8.2

The sizes of these SGA components can be managed in two ways: manually or matically If you choose to manage these components manually, you must specify the size

auto-of each SGA component and then increase or decrease the size auto-of each component ing to the needs of the application If these components are managed automatically, the instance itself will monitor the utilization of each SGA component and adjust their sizes accordingly, relative to a predefined maximum allowable aggregate SGA size

accord-404 Chapter 8 N Introducing Oracle Database 11g Components and Architecture

Oracle 11g provides several dynamic performance views to see the components and sizes

of SGA; you can use V$SGA and V$SGAINFO, as shown here:

SQL> SELECT * FROM v$sga;

NAME VALUE - -Fixed Size 1303916Variable Size 570428052Database Buffers 377487360Redo Buffers 4935680SQL>

Alternatively, you may use the SHOW SGA command from SQL*Plus, as shown here:

SQL> SHOW SGA

Total System Global Area 954155008 bytesFixed Size 1303916 bytesVariable Size 570428052 bytesDatabase Buffers 377487360 bytesRedo Buffers 4935680 bytesSQL>

The output from this query shows that the total size of the SGA is 954,155,008 bytes

This total size is composed of the variable space that is composed of the shared pool, the large pool, the Java pool (570428052 bytes), the database buffer cache (377487360 bytes), the redo log buffer (4935680 bytes), and some additional space (1,303,916 bytes) that stores information used by the instance’s background processes The V$SGAINFO view displays additional details about the allocation of space within the SGA, as shown in the following query:

SQL> SELECT * FROM v$sgainfo;

NAME BYTES RESIZEABLE - - -Fixed SGA Size 1303916 No

Redo Buffers 4935680 NoBuffer Cache Size 352321536 YesShared Pool Size 339738624 YesLarge Pool Size 4194304 YesJava Pool Size 12582912 YesStreams Pool Size 0 YesShared IO Pool Size 0 Yes

Granule Size 4194304 NoMaximum SGA Size 954155008 NoStartup overhead in Shared Pool 46137344 NoFree SGA Memory Available 239075328

12 rows selected

SQL>

The results of this query show in detail how much space is occupied by each component

in the shared pool The components with the RESIZEABLE column with a value of Yes can

be managed dynamically by Oracle 11g.

You can also use EM Database Control to view the sizes of each of the SGA components,

as shown in Figure 8.8 From the home screen, go to the Server tab and click Memory sors to see this

Advi-F I g u r e 8 8 EM Database Control showing SGA components

You’ll learn more about the components in the SGA in the next sections

Database Buffer Cache

The database buffer cache is the area in SGA that caches the database data, holding blocks

from the data files that have been read recently The database buffer cache is shared among all the users connected to the database There are three types of buffers:

Oracle uses a least recently used algorithm (LRU algorithm) to manage the contents of

the shared pool and database buffer cache When a user’s server process needs to put a SQL