RAC之Workload Management(负载管理)

Workload management enables you to manage workload distributions to provide optimal performance for users and applications. Workload management comprises the following:

1>Services—Oracle Database 10g introduces a powerful automatic workload management facility, called services, to enable the enterprise grid vision. Services are entities that you can define in Oracle RAC databases that enable you to group database workloads and route work to the optimal instances that are assigned to offer the service.

(services可以允许我们将整个数据库负载进行分组，然后将不同的工作负载路由到提供该service的最优的实例。)
2>Connection Load Balancing—A feature of Oracle Net Services that balances incoming connections across all of the instances that provide the requested database service.

(将connection分布在提供了我们请求的service的实例上。分为客户端连接负载均衡、服务器端负载均衡)

3>Load Balancing Advisory—Provides information to applications about the current service levels that the database and its instances are providing. The load balancing advisory makes recommendations to applications about where to direct application requests to obtain the best service based on the policy that you have defined for that service.

(负载均衡顾问/咨询 对于负载均衡的实现十分重要，他提供了系统的负载信息。)

4>Fast Application Notification (FAN)—The notification mechanism that Oracle RAC uses to quickly alert applications about configuration and workload service level changes.

5>Runtime Connection Load Balancing—This is the ability of Oracle Clients to provide intelligent allocations of connections in the connection pool based on the current service level provided by the database instances when applications request a connection to complete some work.

6>Fast Connection Failover—This is the ability of Oracle Clients to provide rapid failover of connections by subscribing to FAN events.

7>High Availability Framework—An Oracle RAC component that enables the Oracle Database to maintain components in a running state at all times.

When a user or application connects to a database, Oracle recommends that you specify a service in the connect data portion of the connect string. Oracle Database automatically creates one database service when the database is created. For many installations, this may be all you need. To enable more flexibility in the management of the workload using the database, Oracle Database 10g enables you to create multiple services and specify which instances offer the services.

With Runtime Connection Load Balancing, applications can use load balancing advisory events to provide better service to users. The Oracle JDBC and ODP.NET clients are automatically integrated to take advantage of load balancing advisory events. (load balanceing advisory 的实现需要 Runtime Connection Load Balancing的支持)

oracle推荐使用service来进行负载均衡的配置，而目前实际情况下的RAC，多数都没有利用好service来进行负载均衡。service对于负载均衡十分重要，对于failover也十分重要。RAC环境下的service是一个十分重要的组件，我们应该很好的掌握它。其他的FAN, Load balancing advisory等等都是为service来服务的。