TAF WITH SCAN IN 11GR2

TAF WITH SCAN IN 11GR2

TRANSPARENT APPLICATION

FAILOVER WITH SCAN

Transparent Application Failover is process 

by which the sessions are automatically failover

 to the other available instance in the cluster database.

New connection would be point to the available instance

 on the cluster database and if you have any active

 transaction and it will be rollback to the last committed

transaction.

TRANSPARENT APPLICATION FAILOVER

 (TAF) FAILOVER METHODS

(METHOD = BASIC/PRECONNECT)

BASIC FAILOVER 

The second connection to the available instance is made

 only if and when the primary instance is down or

 disconnected for some reason.

PRECONNECT FAILOVER 

The Second connection to another available instance is

 made at the same time as the connection to the primary 

instance. Having the backup connection already in place

 can reduce the time needed for a failover in the event 

that one needs to take place. We have considered the

 Over Head while the sessions are pre-connected.

TRANSPARENT APPLICATION FAILOVER

 (TAF) FAILOVER TYPE 

(TYPE=SESSION/SELECT/NONE)

SESSION 

When the TYPE= Session specified, it will 

failover to the available instance in the cluster

database and it doesn’t continue with selected,

 if it is in the process. OCI will start the select 

process again.

SELECT

When the type=select specified, 

it will failover to the available 

instance in the cluster database 

and the failover process also 

replays the queries that is in 

the progress.

NONE

No failover function is used. 

When you specify it as none, 

no failover function will be used.




TAF can be configured at the Oracle Client side

 in tnsnames.ora 

or at the Database Server side using srvctl

SRVCTL SYNTAX FOR CREATING SERVICE

srvctl add service -d -s
-r "" [-a ""] 

[-P {BASIC | NONE | PRECONNECT}]
-g [-c {UNIFORM | SINGLETON}]
[-k ]
[-l [PRIMARY][,PHYSICAL_STANDBY][,LOGICAL_STANDBY]

[,SNAPSHOT_STANDBY]]
[-y {AUTOMATIC | MANUAL}]
[-q {TRUE|FALSE}]
[-x {TRUE|FALSE}]
[-j {SHORT|LONG}]
[-B {NONE|SERVICE_TIME|THROUGHPUT}]
[-e {NONE|SESSION|SELECT}] 
       -- This defines the type of TAF whether SESSION

 or SELECT.
[-m {NONE|BASIC}] 
       --This defines the method of TAF.
[-z ] 
       -- the number of times to attempt to connect after a failover.
[-w ]
       -- the amount of time in seconds to wait between connect attempts.

SYNTAX

          srvctl add service -d -s
          -r "" [-a ""]

 [-P {BASIC | NONE | PRECONNECT}]
         [-e {NONE|SESSION|SELECT}]
         [-m {NONE|BASIC}]
         [-z ]
         [-w ]

PRECONNECT USING SCAN NAMES

When you are connecting using the scan names and

 having the failover method as PRE-CONNECT 

then you use should configured with the

 (preferred instance & available instance).

Ex:

Bhuvan =

  (description =

   (address = (protocol=tcp)(host=bhuvanrac-scan)(port=1521))

   (connect_data=

     (service_name=bhuvanrac)

     (failover_mode= (backup=bhuvanrac_preconnect)

       (type=select) (method=preconnect)

     )

   ) )

bhuvanrac_preconnect =

  (description =

   (address = (protocol=tcp)(host=bhuvanrac-scan)(port=1521))

   (connect_data=(service_name=bhuvanrac_preconnect))

  )

BASIC USING SCAN NAMES

SCAN provides load balancing and failover for

 client connections to the database. 

The SCAN works as a cluster alias for databases in the cluster.

bhuvanrac =

  (description =

   (address = (protocol=tcp)(host=bhuvanrac-scan)(port=1521))

   (connect_data=(service_name=bhuvanrac))

  )

TRADITIONAL METHOD

JDBC connection

BHUVAN=(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)

(Host=bhuora01)(Port=1521)) (ADDRESS=(PROTOCOL=TCP)

(HOST=bhuora02)(PORT = 1521))

(CONNECT_DATA=(SERVICE_NAME=BHUVANRAC)

(FAILOVER_MODE=(TYPE=SELECT)(METHOD=BASIC))))

TNS ENTRY

BHUVAN=

(DESCRIPTION=

(ADDRESS=(PROTOCOL=TCP)(Host=bhuora01)(Port=1521))

(ADDRESS=(PROTOCOL=TCP)(HOST=bhuora02)(PORT=1521))

(CONNECT_DATA=(SERVICE_NAME=BHUVANRAC)

(FAILOVER_MODE=(TYPE=SELECT)(METHOD=BASIC))))

Start the service $ srvctl start service -d  -s 

Stop the service 
$ srvctl stop service -d  -s 

To Modify the service

$ srvctl modify service -d  -s 

To see the configuration of the service

$ srvctl config service -d  -s 

To see the Connection of the pre-connect session
select inst_id,username,service_name,failover_type,

 failover_method,failed_over from gv$session where username='BHUVAN';