Shulou(Shulou.com)06/01 Report--

Most of the databases of traditional enterprises such as banking and telecommunications industry use the high-availability architecture of oracle rac+dataguard. In the implementation process of rac project, due to the stringent requirements of business continuity, high-availability implementation and testing work is particularly important.

Oracle has a separate chapter called Ensuring application Continuity in the official rac documentation of the new version of 12cR2. In the previous oracle10g and 11g versions, in order to realize the RAC failover (failover) feature of client, all kinds of applications app and db need to make various configuration adjustments. With the arrival of the new 12cR2 version of oracle, these configuration steps become more simplified.

The following is a brief summary of the failover configuration in the oracle11gR2 environment.

First of all, according to whether pre-existing connections (such as connections in connection pooling) are used, client connections are divided into Connect Time Connection Failover and Runtime Connection Failover,runtime prefixes that refer to cases where connections already exist, such as connection pooling.

1 、 Connect Time Connection Failover

The Failover when connecting to the database can be realized by configuring scan ip and service in the tnsnames.ora of the client.

2 、 Runtime Connection Failover

Oracle implements Runtime Connection Failover through two means, namely TAF (Transparent Application Failover) and FCF (Fast Connection Failover).

The first is TAF:

It can be defined in the connection string in the tnsnames.ora on the client side or in the service on the server side. TAF is only valid for clients and connection pooling that use OCI connections, where OCI connections can be encapsulated on OCI connections. For example, JDBC-OCI driver supports TAF, but JDBC thin driver does not support TAF (because JDBC thin driver is not based on OCI).

The second is FCF:

Fast Connection Failover, which is actually implemented by the client by subscribing to FAN HA events.

Because JDBC thin connections are not based on OCI, Runtime Connection Failover in this case cannot use TAF, only FCF.

If you want the application app to have the TAF attribute, you can make a simple app transformation: first install the oracle client program in the client environment of app, and then adjust the jdbc thin connection to the connection mode of jdbc oci.

In the oracle12cR2 version, failover can be transaction-based, and replay dml statements are much more failover-based than 11g session-based statements.

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