9 Understanding the Oracle Real Application Clusters Installed Configuration

Understanding the Configured Environment in Real Application Clusters

Oracle Net Configuration Assistant (NetCA) and Database Configuration Assistant (DBCA) configure your environment to meet the requirements for database creation and Enterprise Manager discovery of Real Application Cluster databases.

The Oracle Cluster Registry in Real Application Clusters

Database Configuration Assistant uses the Oracle Cluster Registry (OCR) for storing the configurations for the cluster databases that it creates. The OCR is a shared file in a cluster file system environment. If you do not use a cluster file system, then you must make this file a shared raw device. Oracle Universal Installer (OUI) automatically initializes the OCR during the Oracle Clusterware installation.

Database Components Created Using Database Configuration Assistant

This section describes the database components that DBCA creates, which include:

• Tablespaces and Datafiles

• Control Files

• Redo Log Files

Managing Undo Tablespaces in Real Application Clusters

Oracle stores rollback or undo information in undo tablespaces. To manage undo tablespaces, Oracle recommends that you use automatic undo management. Automatic undo management is an automated undo tablespace management mode that is easier to administer than manual undo management.

Initialization Parameter Files

Oracle recommends using the server parameter file (SPFILE). This file resides on the server on the shared disk; all instances in a cluster database can access this parameter file.

Configuring Service Registration-Related Parameters in Real Application Clusters

Two key benefits of RAC are connection load balancing and failover. RAC extends the ability of single-instance Oracle database load balancing, where connections are distributed among local dispatchers, to the balancing of connections among all instances in a cluster database. In addition, RAC provides failover by configuring multiple listeners on multiple nodes to manage client connection requests for the same database service. Connection load balancing and failover increase availability by taking advantage of the redundant resources within a cluster database. These features, however, require cross instance registration.

Cross instance registration in RAC occurs when an instance's PMON process registers with the local listener and with all other listeners. Thus, all instances in the cluster database register with all listeners that run on nodes that run instances of the cluster database. This enables all listeners to manage connections across all instances for both load balancing and failover.

Cross instance registration requires configuring the LOCAL_LISTENER and REMOTE_LISTENER initialization parameters. The LOCAL_LISTENER parameter identifies the local listener and the REMOTE_LISTENER parameter identifies the global list of listeners. The REMOTE_LISTENER parameter is dynamic. Oracle changes the setting for REMOTE_LISTENER dynamically when you reconfigure your cluster database, for example, when you add or delete instances.

By default, DBCA configures your environment with dedicated servers. However, if you select the Shared server option on DBCA, then Oracle configures the shared server. In this case, Oracle uses both dedicated and shared server processing. When shared servers are configured, the DISPATCHERS parameter is specified as in the following example:

DISPATCHERS="(protocol=tcp)"

If the DISPATCHERS initialization parameter does not specify the LISTENER attribute as in the previous example, then the PMON process registers information for all dispatchers with the listeners specified by the LOCAL_LISTENER and REMOTE_LISTENER parameters.

However, when the LISTENER attribute is specified, the PMON process registers dispatcher information with the listeners specified by the LISTENER attribute. In this case, setting the LISTENER attribute overrides REMOTE_LISTENER settings for the specified dispatchers as in the following example:

DISPATCHERS="(protocol=tcp)(listener=listeners_db_name)"

Configuring the Listener File (listener.ora)

You can configure two types of listeners in the listener.ora file as described under the following headings:

• Local Listeners

• Multiple Listeners

• How Oracle Uses the Listener (listener.ora File)

sid.local_listener=listener_sid

listener_sid=(address=(protocol=tcp)(host=node1-vip)(port=1522))

listener_node1= 
  (description= 
    (address=(protocol=ipc)(key=extproc))
    (address=(protocol=tcp)(host=node1-vip)(port=1521)(IP=FIRST))
    (address=(protocol=tcp)(host=node1-ip)(port=1521)(IP=FIRST)))
sid_list_listener_node1= 
  (sid_list= 
    (sid_desc= 
      (sid_name=plsextproc) 
      (oracle_home=/private/system/db) 
      (program=extproc)))

Directory Server Access (ldap.ora File)

If you configure access to a Lightweight Directory Access Protocol (LDAP)-compliant directory server with Oracle Net Configuration Assistant during a Custom Install or Advanced database configuration, an ldap.ora file is created. The ldap.ora file contains the following types of information:

• Type of directory

• Location of the directory

• Administrative context from which this server can look up, create, and modify a net service name, and the database service entries

  See Also:

  Oracle Database Net Services Administrator's Guide for further information about directory naming configuration and directory server access configuration

Net Service Names (tnsnames.ora File)

A tnsnames.ora file is created on each node with net service names. A connect identifier is an identifier that maps to a connect descriptor. A connect descriptor contains the following information:

• The network route to the service, including the location of the listener through a protocol address

• The SERVICE_NAME for an Oracle release 8.1 or later, or SID for pre-8.1 Oracle releases

  Note:

  The SERVICE_NAME parameter you use in tnsnames.ora is singular because you can only specify one service name.

DBCA creates net service names for connections as shown in Table 9-3:

db.us.acme.com= 
 (description= 
  (load_balance=on)
   (address=(protocol=tcp)(host=node1-vip)(port=1521)
   (address=(protocol=tcp)(host=node2-vip)(port=1521) 
  (connect_data=
     (service_name=db.us.acme.com)))

mydatabase.us.acme.com=
  (description =
     (address = (protocol = tcp)(host = node1-vip)(port = 1521))
     (address = (protocol = tcp)(host = node2-vip)(port = 1521))
  (load_balance = yes)
     (connect_data =
   (server = dedicated)
   (service_name = mydatabase.us.acme.com)
   )
   )

db1.us.acme.com=
 (description= 
  (address=(protocol=tcp)(host=node1-vip)(port=1521))
  (connect_data= 
    (service_name=db.us.acme.com)
    (instance_name=db1)))

REMOTE_LISTENER=listeners_db_unique_name

listeners_db.us.acme.com= 
(address_list=
   (address=(protocol=tcp)(host=node1-vip)(port=1521))
   (address=(protocol=tcp)(host=node2-vip)(port=1521)))

sid.local_listener=listener_sid

listener_db1.us.acme.com= 
   (address=(protocol=tcp)(host=node1-vip)(port=1522))

db_svc1.us.acme.com= 
  (description = 
    (address=(protocol=tcp)(host=node1-vip)(port=1521)) 
    (address=(protocol=tcp)(host=node2-vip)(port=1521))
    (load_balance=yes) 
    (connect_data=
        (server = dedicated) 
        (service_name = db_svc1.us.acme.com) 
  )
  )

db_svc2.us.acme.com= 
  (description=
    (address=(protocol=tcp)(host=node1-vip)(port=1521)) 
    (address=(protocol=tcp)(host=node2-vip)(port=1521)) 
    (load_balance=yes) 
    (connect_data =
        (server = dedicated)
        (service_name=db_svc2.us.acme.com)
        (failover_mode =
        (type=select)
        (method=basic)
           (retries=180)
           (delay=5)
     )
     )
     )

db_svc3.us.acme.com=
    (description=
      (address=(protocol=tcp)(host=node1-vip)(port=1521))
      (address=(protocol=tcp)(host=node2-vip)(port=1521))
      (load_balance=yes)
      (connect_data=
        (server=dedicated)
        (service_name=db_svc3.us.acme.com)
        (failover_mode=
        (backup=db_svc3_preconnect.us.acme.com)
        (type=select)
        (method=preconnect)
        (retries=180)
        (delay=5)
   )
   )
   )

db_svc3_preconnect.us.acme.com =
  (description =
    (address = (protocol = tcp)(host = node1-vip)(port = 1521))
    (address = (protocol = tcp)(host = node2-vip)(port = 1521))
    (load_balance = yes)
    (connect_data =
      (server = dedicated)
      (service_name = db_svc3_preconnect.us.amce.com)
      (failover_mode =
        (backup = db_svc3.us.acme.com)
        (type = select)
        (method = basic)
        (retries = 180)
        (delay = 5)
      )
    )
  )

extproc_connection_data.us.acme.com= 
 (description= 
  (address_list= 
    (address=(protocol=ipc)(key=extproc0))
  (connect_data= 
    (sid=plsextproc)))

db.us.acme.com= 
 (description= 
  (load_balance=on)
   (address=(protocol=tcp)(host=node1-vip)(port=1521))
   (address=(protocol=tcp)(host=node2-vip)(port=1521))
  (connect_data=
     (service_name=db.us.acme.com)))

db1.us.acme.com=
 (description=
  (address=(protocol=tcp)(host=node1-vip)(port=1521))
  (connect_data= 
    (service_name=db.us.acme.com)
    (instance_name=db1)))

db2.us.acme.com= 
 (description= 
  (address=(protocol=tcp)(host=node2-vip)(port=1521))
  (connect_data= 
    (service_name=db.us.acme.com)
    (instance_name=db2)))

listeners_db.us.acme.com= 
(address_list=
   (address=(protocol=tcp)(host=node1-vip)(port=1521))
   (address=(protocol=tcp)(host=node2-vip)(port=1521)))

extproc_connection_data.us.acme.com= 
 (description=
  (address_list=
    (address=(protocol=ipc)(key=extproc)))
  (connect_data=
    (sid=plsextproc)
    (presentation=RO)))

Net Services Profile (sqlnet.ora File)

The sqlnet.ora file is automatically configured with:

• The computer's domain

  This domain is automatically appended to any unqualified net service name. For example, if the default domain is set to us.acme.com, then Oracle resolves db in the connect string CONNECT scott/tiger@db as: db.us.acme.com.

• A naming method the server uses to resolve a name to a connect descriptor

  The order of naming methods is as follows: directory naming (for Custom Install or Advanced database configuration options only), tnsnames.ora file, Oracle Names server, and host naming.

The following is a sample sqlnet.ora file created during a preconfigured database configuration install:

SQLNET.AUTHENTICATION_SERVICES= (NTS)
NAMES.DIRECTORY_PATH= (TNSNAMES, EZCONNECT)