10g Database Services for High Availability

Oracle Database Tips by Donald Burleson

A ?database service? is an additional service other than the database configured to manage connections to given database instances. A service is started and kept active by the CRS. Configuring a service can be done using the dbca or srvctl. However, using the dbca is preferable because doing so adds the necessary entries to the tnsnames.ora file.

Figure H.1 demonstrates using the dbca to configure the services past_forms, past_admin, and past_rman for the past database. Services can be configured using the dbca at the time the database is created or after the database is created.

The administrator has planned for the instance past1 to be used for the business forms, and for the instance past2 to be used for administration and rman. The services have been configured so that past_forms will prefer past1 but still have access to past2 in the event of a failure on past1. The opposite is true for past_admin. The service past_rman will only connect to the instance past2.

The TAF (Transparent Application Failover) policy is set in this step as well. The three options are none, basic, and pre-connect. Failover is the concept that if an instance fails, the connection will transfer to an alternate instance. Basic TAF establishes a new connection to an alternate instance when the failure occurs. Pre-connect TAF establishes a second connection to a node that has been configured ?available?. Pre-connect speeds up the failover process, but requires that the backup instance be available for backup connections.

Once services have been defined, they will be listed in the CRS. Use the crs_statuscommand to list them as seen in Figure H.2.

Figure H.3 demonstrates using the srvctl utility to verify and view the configuration of services for the past database.

Services can also be viewed while connected to the database. Figure H.4 demonstrates listing the connections created in this exercise.

After setting up the services desired with the dbca, open the tnsnames.ora file with a text editor and read through the new entries. Figure H.5 shows the entry for the past_forms service just created. Notice that the service name is not the database name.

The srvctl utility can be used to add, remove, start and stop services. The following examples demonstrate these functions using srvctl:

srvctl add service ?d past 's past_forms ?r past1 ?a past2
srvctl remove service ?d past 's past_forms
srvctl start service ?d past 's past_forms
srvctl stop service ?d ?past 's past_forms

For more information about configuring services for high availability, visit http://tahiti.oracle.com  and search for the following documents:

 

WITHIN THE DOCUMENT	SEARCH FOR
Oracle? Database Net Services Reference Guide - Part Number B10776-01	Local Naming Parameters  (tnsnames.ora)
Oracle? Real Application Clusters Deployment and Performance Guide ? Part Number B10768-02	A Services Deployment Example
Oracle? Real Application Clusters Administrator's Guide ? Part Number B10765-02	Server Control (SRVCTL) Reference