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Administering Instances

This chapter describes starting up and shutting down instances. It discusses the following topics:

Starting Up and Shutting Down Instances

This chapter discusses these topics in the following sections:

Starting Instances

This section provides procedures for starting instances with Oracle Parallel Server enabled or disabled by explaining:

Enabling Oracle Parallel Server and Starting Instances

You can start instances using either SQL*Plus or the Oracle Enterprise Manager as described in the Oracle8i Parallel Server Setup and Configuration Guide.

Note:
In Oracle8i, the keywords SHARED, EXCLUSIVE, and PARALLEL are obsolete in the STARTUP and ALTER DATABASE MOUNT statements.

Starting an Instance Using SQL*Plus

Starting Oracle Parallel Server instances is procedurally identical to starting a single instance with these exceptions:

Make sure the PARALLEL_SERVER parameter is set to TRUE in the instance initialization file.
Ensure your Cluster Manager software is running. Detailed instructions on Cluster Manager software administration appear in your operating-system specific documentation. If the Cluster Manager is not available or if Oracle cannot communicate with this component, Oracle displays the error ORA-29701: "Unable to connect to Cluster Manager".

See Also:
For Windows NT, the Cluster Manager is described in your vendor documentation.
Start any required operating system specific processes. For more information about these processes, see your Oracle operating system-specific documentation.

If you use the Oracle Database Configuration Assistant to create your database, specifically request that it create an Oracle Parallel Server database so it sets PARALLEL_SERVER to TRUE in your initialization file. To start a database with Oracle Parallel Server disabled, use the default value of FALSE for the PARALLEL_SERVER parameter on your instance.

See Also:
Oracle8i Parallel Server Concepts for more information about Cluster Manager.

Using RETRY to Mount a Database in Shared Mode

If you attempt to start an instance and mount a database in shared mode while another instance is currently recovering the same database, your new instance cannot mount the database until the recovery is complete.

Rather than repeatedly attempting to start the instance, use the STARTUP RETRY statement. This causes the new instance to retry mounting the database every five seconds until it succeeds or has reached the retry limit. Use the syntax:

   STARTUP OPEN database_name RETRY

To set the maximum number of times the instance attempts to mount the database, use the SQL*Plus SET command with the RETRY option; you can specify either an integer (such as 10) or the keyword INFINITE.

If the database can only be opened by being recovered by another instance, then using the RETRY will not repeat connection attempts. For example, if the database was mounted in exclusive mode by one instance, then trying the STARTUP RETRY command in shared mode does not work for another instance.

Setting and Connecting to Instances

Before you can set instances and connect to them, you must install and configure Net8 for the Oracle Parallel Server nodes and any clients that access these nodes. This allows clients to establish remote connections to the nodes.

SQL*Plus commands operate on the current instance with some exceptions as noted under the next heading. The current instance can be either the local, default instance on which you initiated your SQL*Plus session, or it can be a remote instance. Because the SQL*Plus prompt does not indicate which instance is the current instance, be sure you direct your commands to the correct instance.

Initiating a SQL*Plus session and connecting to the database without specifying an instance directs all SQL*Plus commands to the local instance. In this case, the default instance is also the current instance.

To switch the current instance from the local instance to a remote instance, do one of the following:

Re-execute the CONNECT command specifying a remote instance net service name as in this example:
```
CONNECT SYSTEM/MANAGER@net_service_name
```
Disconnect from the database and execute a SET INSTANCE command as in this example:
```
SET INSTANCE net_service_name
```

Then issue another CONNECT command with only your user ID and password. Specifying a remote instance with the CONNECT command while connected to the database by way of an instance allows you to switch from one instance to another without disconnecting.

The SET INSTANCE and SHOW INSTANCE Commands

When using SET INSTANCE to specify an instance on a remote node for the STARTUP command, the parameter file for the remote instance must be accessible by the local node.

The SHOW INSTANCE command displays the net service name for the current instance. SHOW INSTANCE returns the value "LOCAL" if you have not used SET INSTANCE during the SQL*Plus session.

To reset to the default instance, use SET INSTANCE without specifying a net service name or specify "LOCAL". Do not follow the SET INSTANCE command with the word "DEFAULT"; this indicates a connect string for an instance named "DEFAULT".

The CONNECT Command

Connecting as SYSOPER or SYSDBA allows you to perform privileged operations, such as instance startup and shutdown. Multiple SQL*Plus sessions can connect to the same instance at the same time. SQL*Plus automatically disconnects you from the first instance whenever you connect to another one.

Shutting Down Instances

Shutting down an Oracle Parallel Server instance is procedurally identical to shutting down a single instance with these exceptions:

In Parallel Server, shutting down one instance does not interfere with the operation of other running instances.
To shut down a database mounted in shared mode, shut down every instance in the Parallel Server cluster.
When you shut down an instance abnormally, Oracle forces all user processes running in that instance to log off the database. If a user process is currently accessing the database, Oracle terminates that access and displays the message "ORA-1092: Oracle instance terminated. Disconnection forced". If a user process is not currently accessing the database when the instance shuts down, Oracle displays the message "ORA-1012: Not logged on" upon the next call or request made to Oracle.
After a NORMAL or IMMEDIATE shutdown, instance recovery is not required. Recovery is required, however, after you issue the SHUTDOWN ABORT command or after an instance terminates abnormally. The SMON process of an instance that is still running performs instance recovery for the instance that shut down. If no other instances are running, the next instance to open the database performs instance recovery for any instances needing it.
If multiple SQL*Plus sessions are connected to the same instance simultaneously, all but one must disconnect before the instance can shut down normally. You can use the IMMEDIATE or ABORT option of the SHUTDOWN command to shut down an instance when multiple SQL*Plus sessions (or any other sessions) are connected to it.

See Also:
Oracle8i Administrator's Guide for more information on shutting down Oracle databases.

How Instances Are Affected by SQL*Plus and SQL

The following topics are described in this section:

How SQL*Plus Commands Apply to Instances

Table 4-1 describes how common SQL*Plus commands apply to instances.

***Table 4-1 How SQL*Plus Commands Apply to Instances***

*SQLPlus Command**	Associated Instance
ARCHIVE LOG	Always applies to the current instance.
CONNECT	Applies the default instance if no instance is specified in the CONNECT command.
HOST	Applies to the node running the SQL*Plus session, regardless of the location of the current and default instances.
RECOVER	Does not apply to any particular instance, but rather to the database.
SHOW INSTANCE	Displays information about the current instance, which can be different from the default local instance if you have redirected your commands to a remote instance.
SHOW PARAMETER and SHOWN SGA	Display parameter and SGA information from the current instance.
STARTUP and SHUTDOWN	Always apply to the current instance. These are privileged SQL*Plus commands.

Note:
The security mechanism that Oracle uses when you execute privileged SQL*Plus commands depends on your operating system. Most operating systems have a secure authentication mechanism when logging onto the operating system. On these systems, your default operating system privileges usually determine whether you can use STARTUP and SHUTDOWN. For more information, see your operating system-specific documentation.

How SQL Statements Apply to Instances

Most SQL statements apply to the current instance. For example, the statement ALTER DATABASE ADD LOGFILE only applies to the instance to which you are currently connected, rather than the default instance or all instances.

ALTER SYSTEM CHECKPOINT LOCAL also applies to the current instance. By contrast, ALTER SYSTEM CHECKPOINT or ALTER SYSTEM CHECKPOINT GLOBAL applies to all instances.

ALTER SYSTEM SWITCH LOGFILE applies only to the current instance. To force a global log switch, use the ALTER SYSTEM ARCHIVE LOG CURRENT statement. The THREAD option of ALTER SYSTEM ARCHIVE LOG allows you to archive online redo log files for a specific instance.

4 Administering Instances