Multi Data Sources Cluster Configuration and config.xml

3-16 Oracle Fusion Middleware High Availability Guide ■ Weighted - Requests are balanced across a list of available servers using weights assigned to each server to determine the percentage of requests sent to each Local affinity determines whether clients show a preference to servers that run on the same machine to avoid network latency. If the flag is set to true, then requests are routed across the list of servers on the local machine using the load-balancing algorithm if any local servers are available. If no local servers are available, requests are routed to all available remote servers according to the load-balancing algorithm. If local affinity is set to false, requests are routed across all available servers local and remote based on the load-balancing algorithm. You configure weights as single integer values that are associated with component instances. You can assign weights to components that are not currently in a group, however, the weight is not used unless you later configure the component as a member of a group and select the weighted load-balancing algorithm. The weight is a unitless number. The percentage of requests to be sent to each member is calculated by summing the weights of all available members and dividing the weight for each member by the sum of the weights.

3.13 Multi Data Sources

A multi data source is an abstraction around a group of data sources that provides load balancing or failover processing at the time of connection requests, between the data sources associated with the multi data source. Multi data sources are bound to the JNDI tree or local application context just like data sources are bound to the JNDI tree. Applications look up a multi data source on the JNDI tree or in the local application context java:compenv just as they do for data sources, and then request a database connection. The multi data source determines which data source to use to satisfy the request depending on the algorithm selected in the multi data source configuration: load balancing or failover. A multi data source can be thought of as a pool of data sources. Multi data sources are best used for failover or load balancing between nodes of a highly available database system, such as redundant databases or Oracle Real Application Clusters Oracle RAC.

3.14 Cluster Configuration and config.xml

The config.xml file is an XML document that describes the configuration of a WebLogic Server domain. The domain element in config.xml is the top-level element, and all elements in the domain descend from the domain element. The domain element includes child elements such as the server, cluster, and application elements. These child elements may have children of their own. For example, the server element can include the child elements WebServer, SSL and Log. The Application element includes the child elements EJBComponent and WebAppComponent. Each element has one or more configurable attributes. An attribute defined in config.dtd has a corresponding attribute in the configuration API. For example, the Server element has a ListenPort attribute, and likewise, the Weblogic.management.configuration.ServerMBean has a ListenPort attribute. Configurable attributes are readable and writable, that is, ServerMBean has a getListenPort and a setListenPort method. To learn more about config.xml, see the Oracle Fusion Middleware Using Clusters for Oracle WebLogic Server. High Availability for WebLogic Server 3-17

3.15 About Singleton Services