Configuring Transparent Application Failover
The TAF policy can be configured either in the client-side TNS
connection entry, defining the FAILOVER_MODE parameter within the CONNECT_DATA
section, or at the server-side service attributes. When both methods are
defined, the server-side service attributes take precedence.
The following table
describes the parameters that are associated with the FAILOVER_MODE:
|
Parameter
|
Values
|
Description
|
|
TYPE
|
Session
|
When a user connection is lost due to an instance crash, a new
session is automatically established on a surviving instance. This type of
failover does not support replay of the queries that were in progress.
|
|
Select
|
Re-establishes the lost user
connection on a surviving instance, and replays the queries that were in
progress.
|
|
|
None
|
Is the default mode without failover functionality.
|
|
|
METHOD
|
Basic
|
Re-establishes the lost user
connections at failover time. Doesn't require much work on the backup server
until failover time.
|
|
Preconnect
|
Pre-establishes the connection on another instance to provide
rapid failover facility.
|
|
|
DELAY
|
|
Specifies the amount of time
(in seconds) to wait between connect attempts.
|
|
RETRIES
|
|
Specifies the number of re-attempts to connect after a failover.
|
The following types of transactions do not automatically fail over and
must be restarted by TAF:
- Transactional statements. Transactions involving INSERT, UPDATE, or DELETE statements are not supported by TAF.
- ALTER SESSION statements. ALTER SESSION and SQL*Plus SET statements do not fail over.
- Transactions using temporary segments in the TEMP tablespace and global temporary tables do not fail over.
- PL/SQL package states. PL/SQL package states are lost during failover.
EXECUTE
DBMS_SERVICE.MODIFY_SERVICE (service_name => 'OLTP_SERVICE'
,
aq_ha_notifications => TRUE
,
failover_method => DBMS_SERVICE.FAILOVER_METHOD_BASIC
,
failover_type => DBMS_SERVICE.FAILOVER_TYPE_SELECT
,
failover_retries => 180
,
failover_delay => 5
,
clb_goal => DBMS_SERVICE.CLB_GOAL_LONG);
