Which three statements are true about services when used with transparent application failover (TAF) for an
administrator-managed RAC database?
A.
TAF-enabled sessions fail over to a surviving instance accepting logins for the service.
B.
TAF-settings for the service override TAF settings in TNS entry used by the client.
C.
TAF can restart a query or a transaction after failover.
D.
The TAF settings for a client connections overrides any TAF settings in the service definition.
E.
TAF PRECONNECT requires configuration for the service and in the client TNS entry.
Explanation:
A: SESSION failover. When the connection to an instance is lost, SESSION failover results only in the
establishment of a new connection to another Oracle RAC node; any work in progress is lost. SESSION failover
is ideal for online transaction processing (OLTP) systems, where transactions are small.
C: SELECT failover. With SELECT failover, Oracle Net keeps track of all SELECT statements issued during the
transaction, tracking how many rows have been fetched back to the client for each cursor associated with a
SELECT statement. If the connection to the instance is lost, Oracle Net establishes a connection to another
Oracle RAC node and re-executes the SELECT statements, repositioning the cursors so the client can continue
fetching rows as if nothing has happened. The SELECT failover approach is best for data warehouse systems
that perform complex and time-consuming transactions.
D: Oracle’s answer to application failover is a new Oracle Net mechanism dubbed Transparent Application
Failover. TAF allows the DBA to configure the type and method of failover for each Oracle Net client.
Incorrect Answers:E: In PRECONNECT failover, the application simultaneously connects to both a primary and a backup node.
This offers faster failover, because a pre-spawned connection is ready to use. But the extra connection adds
everyday overhead by duplicating connections.
http://www.dba-oracle.com/art_oramag_rac_taf.htm
A,B,E