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Oracle 10g release 2 load balancing features

Oracle Tips by Burleson Consulting

Oracle 10g release 2 has some exciting new features for the shared pool and load balancing.  As a review, Oracle provides a least-highly-loaded algorithm to load balance incoming transactions among the various components of an Oracle application server environment with the Oracle Web cache, and this is being expanded.  We now see these load balancing features within Oracle 10g release 2:

Web Server Load Balancing:   The web cache component includes Apache extension to load-balance transactions to the least-highly-loaded Oracle HTTP server (OHS).

RAC instance Load Balancing:  Staring in Oracle 10g release 2, Oracle JDBC and ODP.NET provide connection pool load balancing facilities through integration with the new ?load balancing advisory? tool.  This replaces the more-cumbersome listener-based load balancing technique.

ASM Disk load balancing: Oracle's Automatic Storage Management (SAM) now enables a single storage pool to be shared by multiple databases for optimal load balancing.  Shared disk storage resources can alternatively be assigned to individual databases and easily moved from one database to another as processing requirements change.

Data Guard Load Balancing ? Oracle Data Guard allows for load balancing between standby databases.

Listener Load Balancing - If advanced features such as load balancing and automatic failover are desired, there are optional sections of the listener.ora file that must be present

Like the Oracle advisories for the shared pool and data buffer caches (an extension of the v$db_cache_advice view), the 10g load balancing advisory monitors each instance in a RAC environment and post ?feedback events? (using FAN, the fast Application Notification facility).  These feedback events are used by the connection pool (in Oracle HTTP server, via JDBC and OPP.NET to route new transactions to the least highly-loaded of the RAC servers.

In the Oracle whitepaper ?Oracle Database 10g Release 2: A Revolution in Database Technology? whitepaper we see that Oracle monitors the relative ?workload? (using a round-robin technique) on each Grid instance and posts the data to the Automatic Workload Repository, where it is picked-up by the application server:

Database workloads change over time as well as the cluster configuration can change.  It is important to create and allocate database connections based on the most up to date information.

Oracle Database 10g Release 2 Real Application Clusters provides a load balancing advisory.  RAC constantly monitors the workload being executed for each service by each instance providing the service.

This information is published to the Automatic Workload Repository and published to the application using FAN events.  The FAN event includes the current service level provided and a recommendation of what percentage of connections to be directed to each instance.

The integrated Oracle Clients use these events to provide intelligent load balancing of application requests.  Most connection pools use a random or round-robin algorithm to select an idle connection from the pool when the application does a get connection. 

Using FAN events from the load balancing advisory, the connection pool will select the connection currently providing the best service.

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