Time for action – configuring FCF for JDBC connections

Let's see an example of how we can configure FCF for JDBC clients.

  1. In order to run FCF as we configured it, we need to create database services where TAF or aq_ha_notifications is disabled. As we discussed, in 11gR2, it's possible to create role-specific database services so that service is automatically enabled or disabled whenever there is a role change. The following statements can be run on the primary and standby clusters to create a database service for a production service OLTP:
    • For the primary cluster, use the following:
      srvctl add service -d ORCL_PRIM -s OLTP -r prim_node1,prim_node2 -l PRIMARY -q FALSE -e NONE -m NONE -w 0 -z 0
    • For the standby cluster, use the following:
      srvctl add service -d ORCL_STD -s OLTP -r std_node1,std_node2 -l    PRIMARY -q FALSE -e NONE -m NONE -w 0 -z 0

    If needed, the following statements will create a read-only service for reporting on the physical standby database:

    • For the primary cluster, use the following:
      srvctl add service -d ORCL_PRIM -s REPORTING -r prim_node1,prim_node2 -l PHYSICAL_STANDBY -q FALSE -e NONE -m NONE -w 0 -z 0
    • For the standby cluster, use the following:
      srvctl add service -d ORCL_PRIM -s REPORTING -r std_node1,std_node2 -l PHYSICAL_STANDBY -q FALSE -e NONE -m NONE -w 0 -z 0

      Tip

      Create the REPORTING service with the DBMS_SERVICE.CREATE_SERVICE procedure on the primary database so that standby knows about this service through redo transmission.

  2. Now we configure the JDBC clients with the proper CONNECT descriptor.
    "jdbc:oracle:thin:@" +
"(DESCRIPTION_LIST=" +
  "(LOAD_BALANCE=off)" + 
  "(FAILOVER=on)" +
  "(DESCRIPTION=" +
    "(ADDRESS_LIST=" +
    "(LOAD_BALANCE=on)" + 
    "(ADDRESS=(PROTOCOL=TCP)(HOST=PRIMARY_SCAN)(PORT=1521)))" +
    "(CONNECT_DATA=(SERVICE_NAME=OLTP)))" +
  "(DESCRIPTION=" +
    "(ADDRESS_LIST=" +
    "(LOAD_BALANCE=on)" +
    "(ADDRESS=(PROTOCOL=TCP)(HOST=STANDBY_SCAN)(PORT=1521)))" +
   "(CONNECT_DATA=(SERVICE_NAME=OLTP))))";
  3. The JDBC client should set the TCP_CONNTIMEOUT_STR property so that the connection attempt fails over to the next host in the ADDRESS_LIST list after the specified time.
    Properties prop = new Properties(); prop.put(oracle.net.ns.SQLnetDef.TCP_CONNTIMEOUT_STR, ""+5000); // 5000ms pds.setConnectionProperties(prop);
  4. Enable FCF and configure the application to connect to all of the primary and standby ONS daemons.
    pds.setFastConnectionFailoverEnabled(true); 
pds.setONSConfiguration("nodes=prim_node1:6200,prim_node2:6200,std_node1:6200,std_node2:6200");

What just happened?

We've successfully configured FCF for JDBC client connections.

Fast Application Notification (FAN)

FAN is a notification mechanism in which Oracle doesn't wait for clients to detect any database status changes (such as service, instance, or if the database goes up or down), and quickly (as its name implies) informs clients about the events. If FAN is not used, clients need to wait for the TCP timeout duration to fail over to another specified connection. This duration can be very long and not suitable for our failover time target.

Note

If the Data Guard broker is used in a failover, the FAN event is automatically sent to the clients.

In addition to up/down events, FAN also notifies clients with load-balancing advisory events. Clients use this information and connect to the instance with the best response time.

It's possible to take advantage of FAN with the following methods:

  1. If an integrated Oracle client is used, the client application can use FAN without programmatic changes. The integrated clients for FAN events are Oracle database 11g JDBC, Oracle Universal Connection Pool (UCP) for Java, Oracle database 11g ODP.NET, and Oracle database 11g Oracle Call Interface (OCI).

    Tip

    JDBC clients subscribe to ONS daemons and receive FAN events only if FCF is configured on the clients.

  2. Implement FAN server-side callouts on your Database Tier.

What just happened?

Connection failover methods are important pieces of the database high-availability feature, and we've gone through configuring automatic connection failover for Oracle database clients in an RAC and Data Guard environment.

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