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5 Managing the Oracle Instance

This chapter provides background information about the Oracle instance and instructions about how to manage the instance.

This chapter contains the following sections:

Overview of the Oracle Instance and Instance Management

An Oracle database system consists of a database and an Oracle instance.

Database—A database consists of a set of disk files that store user data and metadata. Metadata, or "data about the data," consists of structural, configuration, and control information about the database.

Oracle instanceAn Oracle instance (also known as a database instance) contains the set of Oracle Database background processes that operate on the stored data and the shared allocated memory that those processes use to do their work.

An instance must be started to read and write information to the database. It is the instance that actually creates the database upon receipt of instructions from the Oracle Database Configuration Assistant (DBCA) utility or the CREATE DATABASE SQL statement.

When the database instance is not available, your data is safe in the database, but it cannot be accessed by any user or application.

The properties of an Oracle instance are specified using instance initialization parameters. When the instance is started, an initialization parameter file is read, and the instance is configured accordingly.

This section presents some of the concepts of an Oracle instance and its management. It contains the following topics:

About Initialization Parameters

Managing an Oracle instance includes configuring parameters that affect the basic operation of the Oracle instance. These parameters are called initialization parameters. The Oracle instance reads initialization parameters from a file at startup.

During installation, when you select from one of the preconfigured database workloads available in DBCA, the initialization parameters are optimized for typical use in the environment that you specified. As the number of database users increases and the workload increases, you might need to alter some initialization parameters. You can make these changes using the Initialization Parameter page in Oracle Enterprise Manager Database Control (Database Control), or by using one of the advisors provided by Oracle Database, such as the Memory Advisor. See "Using the Memory Advisors" for more information.

After being read from a file, initialization parameters are retained in memory, where the values for many of them can be changed dynamically. There are two types of files from which these parameters can be read: a text initialization parameter file and a server parameter file. The type of file used to start the instance determines if any dynamic initialization parameter changes you make are persistent across database shutdown and startup.

Server parameter file—The server parameter file is the preferred form of initialization parameter file, and is a binary file that can be written to and read by the database. It must not be edited manually. It is stored on the host computer on which Oracle Database is running. Any changes to it are persistent across database shutdown and startup. Changes are made when you use Database Control to modify one or more initialization parameters, or when Oracle Database itself makes changes for self-tuning purposes.

Note:

When changing an initialization parameter in the server parameter file, you can also specify that the in-memory value be changed, so that your change is reflected immediately in the current instance. If you do not change the in-memory value, the change does not take effect until you shut down and restart the database.

Text initialization parameter file—This type of initialization parameter file can be read by the Oracle instance, but it is not written to by the instance. You can change a text initialization parameter file with a text editor, but changes do not take effect until you shut down and restart the Oracle instance. When you start the instance with this type of file, you can still change many initialization parameters dynamically with Database Control, but only for the current instance. Unless you also edit the text initialization parameter file and make the same change, the change is lost when you shut down and restart the database.

When you create the database with DBCA (as described in "Creating and Managing a Database with DBCA"), a server parameter file is created. This file is then used each time the database is started.

SQL statements exist to create a server parameter file from a text initialization file, to create a server parameter file from the current (in-memory) values of all initialization parameters, and to create a text initialization parameter file from a server parameter file.

See Also:

About Background Processes

The background processes of the Oracle instance manage memory structures, asynchronously perform I/O to write data to a file on a disk, and perform general maintenance tasks. The background processes consolidate functions that would otherwise be handled by multiple Oracle Database programs running for each user process. They monitor other Oracle Database processes to provide increased parallelism for better performance and reliability.

The background processes that are present depend on the features that are being used in the database. The most important background processes are described in Table 5-1.

Table 5-1 Oracle Database Background Processes

Background Process Description

Database writer (DBWn)

The database writer writes modified blocks from the database buffer cache to the files on a disk. Oracle Database allows a maximum of 20 database writer processes.

Log writer (LGWR)

The log writer process writes redo log entries to a disk. Redo log entries are generated in the redo log buffer of the System Global Area (SGA) and the log writer process writes the redo log entries sequentially into an online redo log file.

Checkpoint

At specific times, all modified database buffers in the SGA are written to the datafiles by a database writer process (DBWn). This event is called a checkpoint. The checkpoint process signals DBWn, updates the datafiles and control files of the database, and records the time of this update.

System monitor (SMON)

The system monitor performs instance recovery when a failed instance is restarted.

Process monitor (PMON)

The process monitor performs a recovery when a user process fails. It cleans up the cache and frees resources that the failed process was using.

Archiver (ARCn)

Archiver processes copy the redo log files to archival storage when the log files are full or a log switch occurs. The database must be in archive log mode to run archive processes. For more information, see Chapter 9, "Performing Backup and Recovery".

Manageability monitor (MMON)

This process performs various management-related background tasks, for example:

  • Issuing alerts whenever a given metric violates its threshold value

  • Taking snapshots by spawning additional processes

  • Capturing statistical values for SQL objects that have been recently modified


About Server and Client Processes

In addition to background processes, Oracle Database creates server processes that handle the connection requests of user or client processes. A user connection is composed of two distinct pieces:

  • A client program acting on behalf of the user, such as Oracle Enterprise Manager, SQL*Plus, or an application

  • A server process that handles the connection to the database on behalf of the client program, and that performs much of the work for the client program, such as parsing and running SQL statements, and retrieving and returning results to the client program

Server processes can be either dedicated or shared. When server processes are dedicated, Oracle Database is considered to be running in dedicated server mode. When server processes are shared, Oracle Database is considered to be running in shared server mode. In dedicated server mode, each client process has its own server process. Although a dedicated server process is good for long-running queries and administrative tasks, an idle process or too many dedicated processes can result in an inefficient use of resources.

Using shared server mode eliminates the need for a dedicated server process for each connection. In shared server mode, each client connection request is sent to a dispatcher, which is a process that is responsible for routing requests from connected user processes to a pool of shared server processes and returning the responses back to the appropriate user processes. An idle shared server process picks up a request from a common queue, which means a small number of shared servers can perform the same amount of processing as many dedicated servers. Because the amount of memory required for each user is relatively small, less memory and process management are required, and more users can be supported.

Shared server mode is more efficient at supporting multiple client programs making frequent short-running queries.

About Instance Memory Structure

The sizes of the instance memory structures affect the performance of Oracle Database and are controlled by initialization parameters.

Upon installation, you can choose to let the database manage memory for you automatically, or you can configure some degree of manual memory management. If you configure manual memory management, Oracle Database provides advisors to help you determine appropriate values for memory parameters. For both manual and automatic memory management, Oracle Database sends alerts that identify memory sizing problems that require your attention.

The following sections describe the two important memory areas that you can monitor and size:

See Also:

System Global Area

The System Global Area (SGA) is a shared memory area that contains data and control information for the instance. Multiple users can share data within this memory area and avoid repeated, time-consuming access from a physical disk.

The SGA has several components, as listed in Table 5-2.

Table 5-2 SGA Components

Component Description

Buffer cache

Before any data stored in the database can be queried or modified, it must be read from a disk and stored in memory in the buffer cache. All user processes connected to the database share access to the buffer cache. For optimal performance, the buffer cache should be large enough to avoid frequent disk read and write operations.

Shared pool

The shared pool caches information that is shared among users:

  • SQL statements that can be reused

  • Information from the data dictionary such as user account data, table and index descriptions, and privileges

  • Stored procedures, which are executable code that is stored in the database

Redo log buffer

This buffer improves performance by caching redo information until it can be written to the physical redo log files stored on disk. Redo information and redo log files are discussed in "About Online Redo Log Files".

Large pool

This optional area is used to buffer large I/O requests for various server processes.

Java pool

The Java pool is an area of memory that is used for all session-specific Java code and data within the Java Virtual Machine (JVM).

Streams pool

The Streams pool is an area of memory that is used by the Oracle Streams feature. For more information about Oracle Streams, see Oracle Streams Concepts and Administration.

Result cache

The result cache buffers query results. If a query is run that already has results in the result cache, the database returns results from the result cache instead of rerunning the query. This speeds up the execution of frequently run queries.


Program Global Area

A Program Global Area (PGA) is a memory area used by a single Oracle Database server process. When you connect to an Oracle database instance, you create a session that uses a server process for communication between the client and database instance. Each server process has its own PGA.

The PGA is used to process SQL statements and to hold logon and other session information. A large part of the PGA is dedicated to SQL work areas, which are working memory areas for sorts and other SQL operations.

The amount of PGA memory used and the contents of the PGA depend on whether the instance is running in dedicated server or shared server mode. See Oracle Database Concepts for details. See also "About Server and Client Processes" for more information about dedicated server and shared server modes.

The total memory used by all individual PGAs is known as the total instance PGA memory, and the collection of individual PGAs is referred to as the total instance PGA, or just instance PGA. With Oracle Enterprise Manager Database Control, you set the size of the instance PGA, not individual PGAs.

About Instance Startup and Shutdown

After installation, the Oracle instance is started, and the database is open for access by users with database accounts. At some point, you may want to shut down and restart the instance. This section describes the startup and shutdown processes.

The phrases "starting up and shutting down the Oracle instance" are often used interchangeably with "starting up and shutting down the database."

This section contains the following topics:

About Administration Privileges for Startup and Shutdown

To start up or shut down the Oracle instance, you must connect to the instance with a special connection privilege. There are two of these privileges: SYSDBA for fully empowered database administrators and SYSOPER for users who start up and shut down the database, but have no privileges to access user objects.

When you create an Oracle database, there are two primary administrative user accounts that are automatically created: SYS and SYSTEM. Both of these users have full database administration privileges, but initially, only user SYS or SYSTEM can connect with the SYSOPER privilege. Therefore, until you grant the SYSOPER privilege to other users, you must connect to the Oracle instance as user SYS or SYSTEM to start up and shut down the instance. When connecting (logging in) as user SYS, you must always specify that you are connecting AS SYSDBA.

See Also:

About Instance Startup

When you start the Oracle instance, you typically start it such that the database is open and ready for user connections. However, there are situations in which you may want to start the instance with the database mounted, but not open. An instance can also be started without the database either mounted or open. Thus, there are three stages to starting an instance:

  1. You start the instance using one of the following methods:

    The instance reads the initialization parameter file, allocates SGA memory, and starts the background processes.

  2. If you mount the database, the instance opens the database control file, but does not open the datafiles. The database is now considered to be in the mount state. This state enables you to perform certain administrative functions that cannot be performed when other users are accessing the database. An example of such a function is enabling or disabling redo log archiving. See "About Archived Redo Log Files" for information about redo log archiving.

  3. If you open the database, the instance is first mounted, and then it opens the redo log files and datafiles for the database. The database is now open and available for all user access.

The default startup behavior is to complete the three stages in sequence, transparently. Unless you explicitly specify otherwise, the instance is started and the database is mounted and opened.

About Instance Shutdown

Instance shutdown is the reverse of instance startup. Shutdown goes through these three stages:

  1. You shut down the database using one of the methods discussed in "About Instance Startup". Any modified data blocks cached in the SGA that have not been written to a disk are written. The contents of the redo log buffer are written to a disk, and then the redo log buffer is cleared. A checkpoint is performed on the datafiles and their headers are marked current as of the time the database was closed. Datafiles and log files are closed. Users can no longer access the database.

  2. The Oracle instance dismounts the database and updates relevant entries in the control file to record a clean shutdown. The control file is closed. The database is now closed and dismounted, and only the instance remains.

  3. The Oracle instance stops the background processes and deallocates the shared memory used by the SGA.

Shutting Down and Starting Up the Oracle Instance

This section provides instructions about two methods you can use to start up or shut down the Oracle instance:

Shutting Down and Starting Up Using Oracle Enterprise Manager Database Control

You can shut down and start up the Oracle instance from the Database Home page of Oracle Enterprise Manager Database Control (Database Control).

To shut down and start up the Oracle instance using Database Control:

  1. Go to the Database Home page.

    See "Accessing the Database Home Page".

  2. In the General section of the Database Home page, click Shutdown.

    Description of hp-shutdown-r2.gif follows
    Description of the illustration hp-shutdown-r2.gif

    The Startup/Shutdown Credentials page appears.

    Description of shutdown_credentials.gif follows
    Description of the illustration shutdown_credentials.gif

  3. Enter credentials as follows:

    1. Enter the host computer credentials of the user who installed Oracle Database, or of any user who is authorized to use SQL*Plus.

    2. Enter the database credentials consisting of the user name SYS and the password that you assigned to SYS during the installation.

    3. In the Connect As list, choose the value SYSOPER.

  4. (Optional) Select the Save as Preferred Credential option if you want these credentials to be automatically filled in for you the next time that this page appears.

  5. Click OK.

    A confirmation page appears.

  6. Click Yes.

    The Startup/Shutdown: Activity Information page appears, informing you that the database is being shut down.

  7. After a short period of time, click Refresh to be returned to the Database Home page.

    The Database Home page indicates that the database instance status is Down.

    Description of database_down.gif follows
    Description of the illustration database_down.gif

  8. Click Startup to start up the database.

    The Startup/Shutdown Credential page appears again.

  9. Enter the credentials, and then click OK.

    A confirmation page appears.

  10. Click Yes.

    The Startup/Shutdown: Activity Information page appears, indicating that the database is being started up. When startup is complete, the Login page appears.

  11. Log in to the database (and to Database Control).

    The Database Home page appears indicating that the database instance status is Up.

Shutting Down and Starting Up Using the Windows Services Program

On Microsoft Windows, you can also start up and shut down your Oracle database using the Services program in Control Panel. You must start or stop the following services:

  • OracleServiceSID, which is your Oracle instance.

  • OracleOracle_homeTNSListener, which is your listener. The listener is required for clients to connect to your database.

  • OracleDBConsoleSID, which enables clients to connect to Oracle Enterprise Manager Database Control.

In the preceding service names, SID refers to the system identifier for the instance and Oracle_home refers to the Oracle home name.

To start or stop Oracle Database services:

  1. Do one of the following:

    • On Windows XP and Windows Server 2003, click Start, and then select Control Panel.

    • On Windows 2000 Server, click Start, select Settings, and then select Control Panel.

    The Control Panel window opens.

  2. Double-click the Administrative Tools icon, and then double-click the Services icon.

    The Services window opens, displaying all Windows services that are available on your system.

  3. Locate the Oracle Database services listed at the beginning of this section. For example, if your SID is orcl, then locate the following services:

    • OracleServiceORCL

    • OracleOraDb11g_home1TNSListener

    • OracleDBConsoleorcl

  4. Start or stop all three services, using the following steps for each service:

    1. Select the service name.

    2. In the Action menu, click Start or Stop.

Viewing and Modifying Initialization Parameters

This section provides instructions about viewing the initialization parameter settings for your database and modifying these parameters. Three scenarios are explained for modifying initialization parameters:

Note:

These three scenarios correspond to using the SCOPE=MEMORY, SCOPE=BOTH, and SCOPE=SPFILE clauses of the ALTER SYSTEM SQL statement, respectively, when you use the ALTER SYSTEM SQL statement to change initialization parameters.

To view or modify initialization parameters:

  1. At the top of the Database Home page, click the Server link to view the Server subpage.

  2. Under Database Configuration, click All Initialization Parameters.

    Oracle Enterprise Manager Database Control (Database Control) displays the Initialization Parameters page.

    Description of init_params.gif follows
    Description of the illustration init_params.gif

    The Initialization Parameters page has two subpages:

    • Current—This subpage (the default) displays all initialization parameter values that are currently active (in memory) for the Oracle instance.

    • SPFile—This subpage displays initialization parameter settings in the server parameter file. This subpage is present only when the current instance started up with a server parameter file. The file location is displayed at the top of the subpage.

    See the online Help for the Initialization Parameters page for field descriptions.

  3. (Optional) On either subpage, reduce the number of initialization parameters displayed by doing one or both of the following, and then clicking Go:

    • In the Name field, enter text.

    • Select from one or more of the lists next to the Name field.

    For example, to view only initialization parameters that have the text "dest" anywhere in the parameter name, enter dest in the Name field, and then click Go.

  4. To modify one or more initialization parameters for the currently running instance only, with the modifications being lost when the instance is restarted, complete the following steps:

    1. On the Current subpage, in the Value column, enter new values for the initialization parameters.

      Note:

      If the Value column cannot be written to for a particular initialization parameter, it means that this parameter is not dynamic—that is, it cannot be changed for the current instance.
    2. Ensure that Apply changes in current running instance(s) mode to SPFile is not selected.

    3. (Optional) In the Comments column, enter text explaining the reasons for the changes.

    4. Click Apply.

      A confirmation message appears.

  5. To modify initialization parameters for the currently running instance, and also record the modifications in the server parameter file that will persist when the database is restarted, complete the following steps:

    1. On the Current subpage, in the Value column, enter new values for the initialization parameters.

    2. Select Apply changes in current running instance(s) mode to SPFile.

    3. (Optional) In the Comments column, enter text explaining the reasons for the changes.

    4. Click Apply.

      A confirmation message appears.

  6. To modify initialization parameters in the server parameter file only, such that the current instance is not affected and changes take effect only when the database is next restarted, complete the following steps:

    1. Click the SPFile link to view the SPFile subpage.

    2. (Optional) Reduce the number of entries in the initialization parameter list as described in Step 3.

    3. In the Value column, enter new values for the initialization parameters.

    4. (Optional) In the Comments column, enter text explaining the reasons for the changes.

    5. Click Apply.

      A confirmation message appears.

Note:

Changes to initialization parameters are recorded in the alert log as ALTER SYSTEM statements. See Oracle Database Administrator's Guide for information about the alert log.

Managing Memory

This section provides background information about managing memory for the Oracle instance, and includes instructions about how to adjust the memory allocation for the Oracle instance. It contains the following topics:

About Memory Management

Memory management involves maintaining optimal sizes for the Oracle instance memory structures as demands on the database change. The memory that must be managed is the System Global Area (SGA) memory and the instance Program Global Area (instance PGA) memory. The instance PGA memory is the collection of memory allocations for all individual PGAs.

Beginning with Release 11g, Oracle Database can manage the SGA memory and instance PGA memory completely automatically. You designate only the total memory size to be used by the instance, and Oracle Database dynamically exchanges memory between the SGA and the instance PGA as needed to meet processing demands. This capability is referred to as automatic memory management. In this memory management mode, the database also dynamically tunes the sizes of the individual SGA components and the sizes of the individual PGAs.

If you want to exercise more direct control over the sizes of the SGA and instance PGA, you can use the Memory Advisors page of Database Control to disable automatic memory management and enable automatic shared memory management. When you do this, you also implicitly enable automatic PGA memory management. With automatic shared memory management, you set target and maximum sizes for the SGA. The database then tunes the total size of the SGA to your designated target, and dynamically tunes the sizes of all SGA components. With automatic PGA memory management, you set a target size for the instance PGA. The database then tunes the size of the instance PGA to your target, and dynamically tunes the sizes of individual PGAs.

If you want complete control of individual SGA component sizes, you can use the Memory Advisors page of Database Control to disable both automatic memory management and automatic shared memory management. This effectively enables manual shared memory management. In this mode, you set the sizes of several individual SGA components, thereby determining the overall SGA size. You then manually tune these individual SGA components on an ongoing basis. This mode is intended for experienced DBAs only. Note that in this mode, automatic PGA memory management remains enabled.

Note:

Although it is possible to disable automatic PGA memory management, it is not recommended, and cannot be done using the Memory Advisors page of Database Control.

Table 5-3 summarizes the various memory management modes that you can set using the Memory Advisors page of Database Control.

Table 5-3 Oracle Database Memory Management Modes

Memory Management Mode You Set Oracle Database Automatically Tunes

Automatic memory management

  • Total memory size for this instance

  • (Optional) Maximum memory size for this instance

  • Total SGA size

  • SGA component sizes

  • Instance PGA size

  • Individual PGA sizes

Automatic shared memory management and automatic PGA memory management

(Automatic memory management disabled)

  • SGA target size

  • (Optional) SGA maximum size

  • Instance PGA target size

  • SGA component sizes

  • Individual PGA sizes

Manual shared memory management and automatic PGA memory management

(Automatic memory management and automatic shared memory management disabled)

  • Shared pool size

  • Buffer cache size

  • Java pool size

  • Large pool size

  • Instance PGA target size

  • Individual PGA sizes


Note:

Automatic Memory Management is not available on all platforms. See Oracle Database Administrator's Guide for more information about supported platforms.

If you choose the basic installation option when you install the database, automatic memory management is enabled. If you choose advanced installation, DBCA enables you to select from the three memory management modes. Oracle recommends that you enable automatic memory management.

Whichever memory management mode you choose, you may have occasion to adjust memory settings as demands on the database or on its host computer change. Reasons why you adjust memory settings include the following:

  • You receive a memory-related alert or error message.

  • You receive a memory-related recommendation from Automatic Database Diagnostic Monitor (ADDM).

  • You want to change the amount of memory allocated to accommodate future growth in memory demand.

You can use a memory advisor to help you adjust memory sizes. See "Modifying Memory Settings – Automatic Shared Memory Management" for an example of using a memory advisor.

Enabling Automatic Memory Management

If you did not enable automatic memory management when you installed and configured your database, Oracle recommends that you do so after installation, unless you are an experienced DBA with specific reasons to manually tune memory sizes. With automatic memory management, the Oracle instance dynamically tunes all memory components to optimize performance as the workload changes.

To enable automatic memory management:

  1. Go to the Database Home page, logging in as user SYS.

    See "Accessing the Database Home Page".

    Note:

    You must log in as user SYS to change the maximum memory size, which is a static initialization parameter.
  2. At the top of the page, click Server to view the Server subpage.

  3. In the Database Configuration section, click Memory Advisors.

    The Memory Advisors page appears with the SGA subtab displayed by default.

  4. If the Maximum SGA Size field already contains a positive number that is greater than or equal to the desired total amount of memory to allocate to the database, skip to Step 13.

  5. In the Maximum SGA Size (MB) field, enter the maximum permissible size for database memory.

    Use the sum of the current sizes of the SGA and instance PGA as a guideline, and optionally add some room for growth.

  6. Click Apply.

    A confirmation page appears, indicating that you must restart the database.

  7. Click Yes.

    The Restart Database: Specify Host and Target Database Credentials page appears.

  8. Enter host credentials and database credentials.

    Supply host credentials for any operating system user that has execute permission on SQL*Plus. Supply database credentials for a database user with the SYSDBA privilege (such as the user SYS).

  9. Click OK.

    The Restart Database: Confirmation page appears.

  10. Click Yes to proceed with database restart.

  11. Wait a few minutes, and then click Refresh.

    The Database Home page appears.

  12. Return to the Memory Advisors page.

  13. Next to Automatic Memory Management Disabled, click Enable.

    The Enable Automatic Memory Management page appears.

  14. In the field titled Total Memory Size for Automatic Memory Management, enter the desired amount of memory to allocate to the database, and then click OK.

    A confirmation message appears.

Modifying Memory Settings – Automatic Memory Management

Modifying memory settings for automatic memory management involves using the Memory Advisors page of Database Control to change the total memory size setting. The procedure for changing this setting differs depending on whether or not your desired new setting exceeds the current setting for maximum memory size. If the new setting exceeds the maximum memory size setting, you must first increase the maximum memory size accordingly.

To modify total memory size (new value does not exceed maximum memory size):

  1. Go to the Database Home page.

    See "Accessing the Database Home Page".

  2. At the top of the page, click Server to view the Server subpage.

  3. In the Database Configuration section, click Memory Advisors.

    The Memory Parameters page appears.

    Description of mem_param_auto.gif follows
    Description of the illustration mem_param_auto.gif

  4. Do one of the following:

    • In the Total Memory Size field, enter a new value that is less than or equal to the value in the current Maximum Memory Size field.

    • To use the Memory Advisor to help you choose a new size, click Advice.

      The Memory Size Advice page appears.

      Click a point on the curve to change the total memory size. The new size is displayed below the graph. Continue clicking the curve until the desired value is displayed, and then click OK.

  5. On the Memory Advisors page, click Apply.

    A confirmation message appears.

To modify total memory size (new value exceeds maximum memory size):

  1. Go to the Database Home page, logging in as user SYS.

    See "Accessing the Database Home Page".

    Note:

    You must log in as user SYS to change the maximum memory size, which is a static initialization parameter.
  2. At the top of the page, click Server to view the Server subpage.

  3. In the Database Configuration section, click Memory Advisors.

    The Memory Advisors page appears.

  4. In the Maximum Memory Size (MB) field, enter a new value for the maximum total memory to allocate to the database.

    This value must be greater than or equal to the desired new value for total memory size.

  5. Click Apply.

    A confirmation page appears, indicating that you must restart the database.

  6. Click Yes.

    The Restart Database page appears.

  7. Enter host credentials and database credentials.

    Supply host credentials for any user that has execute permission on SQL*Plus. Supply database credentials for a database user with the SYSDBA privilege (such as user SYS).

  8. Click OK.

    The Restart Database: Confirmation page appears.

  9. Click Yes to proceed with database restart.

  10. Wait a few minutes, and then click Refresh.

    The Database Home page appears.

  11. Return to the Memory Advisors page.

  12. Do one of the following:

    • In the Total Memory Size field, enter a new value that is less than or equal to the value in the current Maximum Memory Size field.

    • To use the Memory Advisor to help you choose a new size, click Advice.

      The Memory Size Advice page appears.

      Click a point on the curve to change the total memory size. The new size is displayed below the graph. Continue clicking the curve until the desired value is displayed, and then click OK.

  13. On the Memory Advisors page, click Apply.

    A confirmation message appears.

See Also:

Modifying Memory Settings – Automatic Shared Memory Management

Modifying memory settings for automatic shared memory management involves using the Memory Advisors page of Database Control to change the total SGA size. This section assumes that automatic memory management is disabled, that automatic shared memory management is enabled, and that the desired new value for the total SGA size does not exceed the current value for maximum SGA size.

Note:

If you want a new total SGA size that exceeds the current value for maximum SGA size, you must first log in as user SYS, change the maximum SGA size, and restart the database. A similar procedure is described in "To modify total memory size (new value exceeds maximum memory size):".

To modify the total SGA memory size:

  1. Go to the Database Home page.

    See "Accessing the Database Home Page".

  2. At the top of the page, click Server to view the Server subpage.

  3. In the Database Configuration section, click Memory Advisors.

    The Memory Advisors page appears, with the SGA subpage shown.

    Description of mem_current_allocation.gif follows
    Description of the illustration mem_current_allocation.gif

  4. In the Current Allocation section, do one of the following:

    • In the Total SGA Size (MB) field, enter a new total size for the SGA.

    • To use the SGA Advisor to help you choose a new SGA size, click Advice.

      The SGA Size Advice window opens.

      Description of mem_allocation_advice.gif follows
      Description of the illustration mem_allocation_advice.gif

      Click a point on the curve to change the total SGA size. The new SGA size is displayed below the graph. Continue clicking the curve until the desired value is displayed, and then click OK.

      This example graph shows that at the current time, increasing the total SGA size is not expected to provide any gain in performance.

  5. On the Memory Advisors page, click Apply.

    A confirmation message appears.

See Also:

Modifying Memory Settings – Automatic PGA Memory Management

Modifying memory settings for automatic PGA memory management involves using the Memory Advisors page of Database Control to modify the instance PGA size. This section assumes that automatic memory management is disabled, and that automatic PGA memory management is enabled.

Note:

When you disable automatic memory management, automatic PGA memory management is enabled by default.

To modify the instance PGA size:

  1. Go to the Database Home page.

    See "Accessing the Database Home Page".

  2. At the top of the page, click Server to view the Server subpage.

  3. In the Database Configuration section, click Memory Advisors.

    The Memory Advisors page appears, with the SGA subpage shown.

  4. Click PGA to view the PGA subpage.

    Description of mem_param_pga.gif follows
    Description of the illustration mem_param_pga.gif

  5. Do one of the following:

    • In the Aggregate PGA Target field, enter a new size for the instance PGA.

    • To use the PGA Advisor to help you choose a new instance PGA size, click Advice.

      The PGA Aggregate Target Advice window appears. Click a point on the curve to change the instance PGA size, and then click OK.

    See Oracle Database Performance Tuning Guide for information about sizing the instance PGA.

  6. Click Apply.

    A confirmation message appears.

See Also:

Instances: Oracle By Example Series

Oracle By Example (OBE) has a series on the Oracle Database 2 Day DBA guide. This OBE steps you through the tasks in this chapter, and includes annotated screenshots.

To view the Instances OBE, in your browser, enter the following URL:

http://www.oracle.com/webfolder/technetwork/tutorials/obe/db/11g/r1/2day_dba/instance/instance.htm