Database Reference
In-Depth Information
CHAPTER 33
■ ■ ■
Session Disconnection, Load
Rebalancing, and TAF
N one of the manuals, including the latest Oracle11 g release 1 editions, indicate any link
between ALTER SYSTEM DISCONNECT SESSION and Transparent Application Failover (TAF). This is
also true for a transactional shutdown of an instance, that is, a shutdown operation, which is
deferred until all clients have committed or rolled back their work, with the command SHUTDOWN
TRANSACTIONAL . A third undocumented link exists between the disconnection of sessions with
the PL/SQL package DBMS_SERVICE in Oracle10 g as well as Oracle11 g and TAF.
The SQL statement ALTER SYSTEM DISCONNECT SESSION , the SQL*Plus command SHUTDOWN
TRANSACTIONAL , and the PL/SQL package DBMS_SERVICE may be used to gracefully disconnect
and reconnect database sessions that have Transparent Application Failover enabled, to another
DBMS instance. This feature is useful in cases where maintenance needs to be performed. It is
also useful in a scenario where load needs to be rebalanced among DBMS instances in a RAC
cluster, after one or more nodes had intermittently been unavailable.
Introduction to Transparent Application Failover
Transparent Application Failover is an automatic database session reestablishment feature
built into Oracle Call Interface (OCI). It is primarily intended for RAC environments to reestablish
database sessions in case of cluster node failure, but the functionality as such is fully independent
of RAC and may be used for single instance as well as Data Guard environments. TAF does not
work with the JDBC Thin driver, since that driver is not built on top of OCI. Following is an
example of a Net service name configured with Transparent Application Failover:
taftest.oradbpro.com =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = dbserver1)(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = dbserver2)(PORT = 1521))
)
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