Examples of TAF Configurations

October 23, 2003
Don Burleson

The following is a list of several examples of TAF configurations:

· Connect-Time Failover with Client Load Balancing

· Retry of connections

· Pre-established failover connections

TAF with Connect-Time Failover and Client Load Balancing

To implement TAF with connect-time failover and client load balancing for multiple addresses, configure the tnsnames.orafiles as shown below. Oracle Net connects randomly to one of the protocol addresses on aultlinux1 or aultlinux2. If the instance were to fail after the connection, the TAF application fails over to the other node's listener, reissuing any select statements in flight.

ault=

(DESCRIPTION=

(LOAD_BALANCE=on)

(FAILOVER=on)

(ADDRESS=

(PROTOCOL=tcp)

(HOST=aultlinux1)

(PORT=1521))

(ADDRESS=

(PROTOCOL=tcp)

(HOST=aultlinux2)

(PORT=1521))

(CONNECT_DATA=

(SERVICE_NAME=ault)

(FAILOVER_MODE=

(TYPE=select)

(METHOD=basic))))

Configuring TAF to Retry a Connection

With a proper configuration, TAF will automatically retry connecting if the first connection attempt fails. The tnsnames.orafile is configured with the retries and delay parameters. In the example shown below, Oracle Net tries to reconnect to the listener on the aultlinux1 server. If the failover connection fails, Oracle Net waits 10 seconds before trying to reconnect again. Using this tnsnames.ora file Oracle Net attempts to reconnect up to 10 times.

ault=

(DESCRIPTION=

(ADDRESS=

(PROTOCOL=tcp)

(HOST=aultlinux1)

(PORT=1521))

(CONNECT_DATA=

(SERVICE_NAME=ault)

(FAILOVER_MODE=

(TYPE=select)

(METHOD=basic)

(RETRIES=10)

(DELAY=10))))

Configuring TAF for Pre-Establishing Connections

TAF can be configured to create pre-established connections to a second instance. The initial and backup connections are explicitly specified. In the example below, clients that use net service name ault1 to connect to the listener on aultlinux1 are also pre-connected to aultlinux2. If the aultlinux1 fails after the connection, Oracle Net automatically fails over to aultlinux2, reissuing any select statements in progress. In this reciprocal setup, Oracle Net pre-connects to aultlinux1 for those clients that use ault2 to connect to the listener on aultlinux2.

ault1 =

(DESCRIPTION=

(ADDRESS=

(PROTOCOL=tcp)

(HOST=aultlinux1)

(PORT=1521))

(CONNECT_DATA=

(SERVICE_NAME=ault)

(INSTANCE_NAME=ault1)

(FAILOVER_MODE=

(BACKUP=ault2)

(TYPE=select)

(METHOD=preconnect))))

ault2=

(DESCRIPTION=

(ADDRESS=

(PROTOCOL=tcp)

(HOST=ault2)

(PORT=1521))

(CONNECT_DATA=

(SERVICE_NAME=ault)

(INSTANCE_NAME=ault2)

(FAILOVER_MODE=

(BACKUP=ault1)

(TYPE=select)

(METHOD=preconnect))))

Verifying TAF Configurations

The v$sessionview contains the failover_type, failover_method, and failed_over columns. These columns are used to monitor connected clients and the TAF status. An example select against this view is shown below.

SELECT MACHINE, FAILOVER_TYPE, FAILOVER_METHOD, FAILED_OVER, COUNT(*)

FROM V$SESSION

GROUP BY MACHINE, FAILOVER_TYPE, FAILOVER_METHOD, FAILED_OVER;

The output before failover of the aultlinux1 server resembles the following:

MACHINE FAILOVER_TYPE FAILOVER_M FAI COUNT(*)

-------------- ------------- ---------- --- ----------

aultlinux1 NONE NONE NO 11

aultlinux2 select PRECONNECT NO 1

The output after a failover from the aultlinux1 server is:

MACHINE FAILOVER_TYPE FAILOVER_M FAI COUNT(*)

---------------- ------------- ---------- --- --------

aultlinux2 NONE NONE NO 10