Load metrics is a collection of system statistics that define a load on a server. Each server in a cluster is assigned a value, or normalized load, based on the load metrics.
Many factors affect overall system performance and throughput of a server. The load metrics that EAServer uses to determine the normalized load are:
CPU utilization
Method response time
IIOP connections
When overall cluster load is light, incoming requests are evenly distributed to all member servers; that is, all member servers have some load. When the cluster becomes more loaded, the load is distributed according to a server’s current load.
Various system load metrics are collected at each sampling interval by the load collector in each server. At each broadcasting interval, the load collector broadcasts its load metrics to all member servers. At each calculating interval the load collectors in the name servers calculate and generate a normalized load list (NLL) of all member servers sorted according to their load metrics. The NLL consists of two elements: the server name and normalized load number. For example, a three-server cluster may have an NLL of:
(Jaguar_server_A, 5), (Jaguar_server_B, 3), (Jaguar_server_C, 1)
Which indicates that the load of Jaguar_server_A is five times greater than the least-loaded server, Jaguar_server_C.A normalized load number ranges from 1 to 5 and is generated by combining all weighted load metrics. A value of 5 indicates a heavily loaded server, while a 1 indicates a lightly loaded server.
All name servers have their own copies of the NLL, which reflects the Naming Service’s view of system-wide load distribution that remains static for an entire refresh interval.
The NLL is referenced to balance the load of a cluster if an adaptive load distribution policy is used. See “Load distribution policies” for information about the various distribution policies.
