Load-Balancing Policies

Load balancing improves performance of the scalable service, both in response time and in throughput.

Two classes of scalable data services exist: pure and sticky. A pure service is one where any instance can respond to client requests. A sticky service has the cluster balancing the load for requests to the node. Those requests are not redirected to other instances.

A pure service uses a weighted load-balancing policy. Under this load-balancing policy, client requests are by default uniformly distributed over the server instances in the cluster. For example, in a three-node cluster where each node has the weight of 1, each node services one-third of the requests from any client on behalf of that service. Weights can be changed at any time through the clresource(1cl) command interface or through the Sun Cluster Manager GUI.

A sticky service has two types: ordinary sticky and wildcard sticky. Sticky services allow concurrent application-level sessions over multiple TCP connections to share in-state memory (application session state).

Ordinary sticky services permit a client to share state between multiple concurrent TCP connections. The client is said to be “sticky” toward the server instance listening on a single port. The client is guaranteed that all requests go to the same server instance, if that instance remains up and accessible and the load balancing policy is not changed while the service is online.

Wildcard sticky services use dynamically assigned port numbers, but still expect client requests to go to the same node. The client is “sticky wildcard” over ports toward the same IP address.