Adaptive Server uses the load score for each instance to determine:
How best to distribute incoming connections – login redirection.
Whether to migrate existing connections – dynamic load distribution.
Load distribution is performed only for a logical cluster running on multiple instances. The Sybase load distribution strategy is to redirect work when one instance is overloaded and other instances are available. It does not seek to maintain perfectly balanced load scores. As a result, Adaptive Server maintains load thresholds for login redirection and dynamic load distribution. The load threshold is the percentage difference between the load on the current instance and the load on the least loaded instance currently participating in a logical cluster. That value must be met before Adaptive Server redirects a login or migrates an existing connection.
Adaptive Server maintains separate load thresholds for login redirection and connection migration. Typically, the login redirection threshold is lower than that for connection migration. You can use sp_cluster profile to configure the load thresholds when creating a load profile.
The load threshold tells Adaptive Server when to redirect connections from an overloaded instance to the least loaded instance. The hysteresis value guards against migration when the threshold value is met, but the actual load scores are too low to require migration.
For example, suppose the load score on the current instance is 2 and that of the least loaded instance is 1. The percentage difference is 100%, which meets the load threshold, but the actual load scores are so low migration is not appropriate.
