9 Understanding the Oracle Real Application Clusters Installed Configuration

9.1 Understanding the Configured Environment in Oracle Real Application Clusters

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

9.2 Oracle Cluster Registry in Oracle Real Application Clusters

DBCA uses 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.

9.3 Oratab Configuration for Oracle Real Application Clusters

Oracle creates an entry for each RAC database in the oratab configuration file. Oracle Enterprise Manager uses this file during service discovery to determine the name of the RAC database, and to determine if the database should be automatically started when the system is restarted. The database entry has the following syntax:

db_unique_name:$ORACLE_HOME:N

The variable db_unique_name is the database name for your RAC database, $ORACLE_HOME is the directory path to the database, and N indicates that the database should not be started at restart time. The following is an example entry for a database named db:

db:/private/system/db:N

9.4 Database Components Created Using Database Configuration Assistant

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

• Tablespaces and Data files

• Control Files

• Redo Log Files

9.5 Managing Undo Tablespaces in Real Application Clusters

Oracle Database 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.

9.6 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.

9.7 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 process monitor (PMON) 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 when using DBCA, then Oracle configures the shared server. In this case, Oracle Database 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)"

9.8 Configuring the Listener File (listener.ora)

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

• Local Listeners

• Multiple Listeners

• How Oracle Database 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)))

9.9 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 database service entries

  
  

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

  
  

9.10 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 9-2.

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)))

9.11 Net Services Profile (sqlnet.ora File)

Oracle Universal Installer starts Oracle Net Configuration Assistant after the database is installed, and creates the Net Services profile, or sqlnet.ora file.

By default, the sqlnet.ora file is located in the following directory:

$ORACLE_HOME/network/admin

In this directory, in addition to the default sqlnet.ora file generated during installation, you also can find a sample sqlnet.ora file in the directory sample.

During installation, Oracle Net Configuration Assistant creates the following entries in the sqlnet.ora file:

NAMES.DIRECTORY_PATH=(TNSNAMES, EZCONNECT)

The parameter NAMES.DIRECTORY_PATH specifies the priority order of the naming methods to use to resolve connect identifiers to connect descriptors.

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

The Easy Connect naming method eliminates the need for service name lookup in the tnsnames.ora files for TCP/IP environments. With Easy Connect, clients use a connect string for a simple TCP/IP address, consisting of a host name and optional port and service name. If you use this method, then no naming or directory system is required.