WebLogic and RAC Database

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WebLogic is a popular java application server that codes and deploys web applications. WebLogic supports connectivity to the Oracle database through JDBC drivers. Code that opens a connection to a database can be inserted into web pages or applications in the presentation or business layer. Thick clients, such as standalone Java applications, can connect to remote databases with RMI. Thin clients can embed database connection code in servlets and JSP tags. Both EJB session beans and entity beans can also use JDBC to connect to the Oracle database.

WebLogic has an advanced feature called connection pooling that opens a specified number of connections upon startup.

Connecting to a database using a WebLogic Server in a two-tier configuration involves creating a java.util.Properties object describing the connection. This object contains name-value pairs containing information such as user name, password, database name, server name, and port number.

For example:

Properties props = new Properties();
props.put("user", "appowner");
props.put("password", "f514");
props.put("server", "ault1");

The server name, ault1 in the preceding example, refers to an entry in the tnsnames.ora file, which is located in the Oracle client installation. The server name defines host names and other information about an Oracle database instance. Once the tnsnames.ora entry is in use, the TAF facility suitable for the Oracle RAC database can be used.

A WebLogic connection pool consists of a group of JDBC connections that are created when the connection pool is registered. This is done either by starting up the WebLogic Server or by assigning the connection pool to a target server or cluster. Connection pools use type 2 or type 4 JDBC drivers to create physical database connections. An application borrows a connection from the pool, uses it, and then returns it to the pool by closing it.

MultiPool is a group of connection pools. MultiPool helps in:

* Load Balancing:  Pools in WebLogic are accessed using a standard round-robin method. When moving to a new connection, the WebLogic Server will select a connection based on the next connection pool in the specified order.

* High Availability:  Connection pools are listed in the order that determines when connection pool switching occurs. The WebLogic Server provisions database connections from starting with the first connection pool on the list. If for some reason that connection pool fails, it uses the others specified in order.

As shown in Figure 11.6, there are two connection pools. Each of the connection pools can be configured to access a particular database instance of the Oracle RAC.

Figure 11.6: WebLogic with JDBC MultiPool Architecture

All of the connections in a given connection pool are identical, but the connections within a multipool can vary. These pools can be configured to access different instances of the same database, as with the Oracle RAC. In this way, the instances are effectively used and the database resources are load balanced.

This feature is particularly useful even if the JDBC thin driver is used. When a type 2 JDBC driver or WebLogic jDriver for Oracle is used, the tnsnames.ora connect string entry can be specified. The TNS entry can be based on a TAF configuration so that load balancing and failover features can be defined.