Configuration Prerequisites Configuring a Cache Cluster for Caches Using the Same Oracle WebLogic Server

3-14 Oracle Fusion Middleware Administrators Guide for Oracle Web Cache More connections are used when another cache cluster member contains little or no data in its cache, such as when it is initially started, when it recovers from a failure, or after invalidation. During this time, the cluster member sends many of the requests to its peers, the owners of the content. In most cases, these requests are served more quickly than requests to the origin server. Having a higher number of connections increases performance during this time and shortens the time it takes to fully load the cache. After a cache is fully loaded, fewer of the connections are used. There is no overhead for unused connections. ■ As the relative capacity of the cache cluster member. The capacity of a cache cluster member is weighted against the total capacity of all active cache cluster members. When you set the capacity, Oracle Web Cache assigns a percentage of the ownership array to the cluster member, indicating how much of the cached content is to be owned by the cluster member. The percentage is calculated using the following formula: cluster_member_capacity total_capacity_of_all_active_cluster_members For example, if cache cluster member Cache_A has a capacity of 100 and cache cluster member Cache_B has a capacity of 300, for a total capacity of 400, Cache_A is assigned 25 percent of the ownership array and Cache_B is assigned 75 percent of the ownership array. That means that Cache_A owns 25 percent of the cached content. Note that in calculating the relative capacity, Oracle Web Cache considers the capacity of active cluster members; it does not consider the capacity of cluster members that it has determined to have failed. Set the initial capacity for each cache cluster member to 10 percent of the Maximum Incoming Connections setting. After you have a better idea of an applications capacity needs and hit rates, fine tune the capacity. If these two assumptions apply to your cache cluster, then apply the following formula to determine the capacity for each cluster member: 1. Incoming traffic is distributed equally to all the cache cluster members. 2. Ownership of content is distributed equally among all the cache cluster members. In the following formula, pick the highest value between the default value or the max_ incoming_connections formula: maxdefault_value, max_incoming_connections cacheable_misses100 number_ of_caches - 1 number_of_caches In the formula: ■ default_value is: – 100 for production environments – 30 for test environments – 0 for invalidation-only clusters When the capacity increases, the number of file descriptors needed by Oracle Web Cache also increases. See Section 3.6.7 for further information about invalidation-only clusters. ■ max_incoming_connections is the Maximum Incoming Connections setting from the Resource Limits page of Fusion Middleware Control. Configuring High Availability Solutions 3-15 ■ cacheable_misses is the percentage of requests for cacheable objects that were not served directly by Oracle Web Cache, but were served by Oracle Web Cache after it fetched the content from the origin server. You can find the Cacheable Misses setting in the Web Cache Statistics page of Fusion Middleware Control. For example, assume a cache cluster with four members. If Oracle Web Cache is operating at 1500 maximum incoming connections, with a 30 percent cacheable miss rate, then the equation to calculate capacity for this configuration looks like the following: 1500 30100 4 - 1 4 The equation calculates to 337.5. You would round up to 338, which is the capacity you would then enter for each cache cluster member. 1500 .3 3 4 = 337.5 If you assign a capacity of 0 to a cluster member, that cluster member does not receive requests from other cluster members. However, that cluster member does forward requests to other cluster members, the owners of the content. If you assign a capacity of 0 to all cluster members, Oracle Web Cache does not forward requests between cluster members. Even when capacity is set to 0, you can still synchronize the configuration and Oracle Web Cache can automatically propagate invalidation requests to cluster members.

3.6.3 Task 1: Add Caches to the Cluster and Configure Properties

Before you add a cache to the cluster, ensure the conditions described in Section 3.6.1 are met. To add cache members to a cluster with Fusion Middleware Control: 1. Navigate to the Web Cache Home page in Fusion Middleware Control for an Oracle Web Cache instance. See Section 2.6.2 .

2. From the Web Cache menu, select Administration and then select Cluster.

The Cluster page displays. 3. For each cache member you want to add:

a. Click Add.

b. In the Component field, enter the name of the cache member.

The Capacity field is auto-filled with a default value. You can modify this value. See Section 3.6.2 for more information about capacity.

4. In the Failover Threshold field, enter the number of allowed consecutive request

failures before Oracle Web Cache considers another cache cluster member to have failed. The default is five failures. See Section 3.6.2 for further information about this field.

5. In the Ping URL field, enter the URL that cache cluster members uses to attempt to

contact a cache cluster member that has reached its failover threshold. Use a URL that is cacheable and that you can guarantee is stored in each cache. The default is _oracle_http_server_webcache_static_.html, which is stored in the cache.