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
Hi
For me should be A,B,E
http://docs.oracle.com/database/121/RACAD/hafeats.htm#RACAD8268
Regards
Indeed A,B,E
http://docs.oracle.com/database/121/NETAG/advcfg.htm#NETAG455
B correct.
The TAF setting on a service overrides any TAF setting in the client connection definition.
http://docs.oracle.com/database/121/RACAD/hafeats.htm#RACAD8268
E is correct
[oracle@rac1 ~]$ srvctl add service -d dell -s testsrv -r dell1 -a dell2 -P preconnect
(failover_mode= (backup=testsrv_preconnect)(type=select)(method=preconnect))
http://practical-tech.blogspot.com/2012/09/oracle-rac-11gr2-server-side-taf-using_24.html
C wrong: TAF only restart query not restart transaction.
TAF can restart a query after failover has completed but for other types of transactions, such as INSERT, UPDATE, or DELETE, the application must rollback the failed transaction and resubmit the transaction.
http://docs.oracle.com/database/121/RACAD/hafeats.htm#RACAD8268