Release 10.1A: OpenEdge Getting Started:
Installation and Configuration

> ## Understanding load balancing

> Load balancing is a feature that allows client connection requests to be distributed among multiple Unified Broker instances that support the same Application Service. Load balancing is a NameServer option that comes installed with some products (for example, the WebSpeed Enterprise Transaction Server) or that you must install as an option with others (for example, the AppServer). If you have load balancing with your product, the NameServer assigns client connections to the appropriate Unified Broker instances based on weight factors that you specify.

> If the weight factor that you specify for each Unified Broker instance is appropriate in relation to the others, the effect is to assign more connections to broker instances with greater resources, and thus to balance connection load among all the instances. You can set the load-balancing weight factor for each Unified Broker instance in the Progress Explorer or by editing the `priorityWeight` property in the `ubroker.properties` file.

> ##### Percentage weight factors

> Properly specified, weight factors give some sense of the amount of work that an individual Unified Broker instance can handle. For example, Table E–1 shows the effect of weight factors specified for three Unified Broker instances registered to support the same Application Service.

> Table E–1: Weight factors based on percentage
> Unified Broker name | Weight factor | Percent of time selected
> --- | --- | ---
> AS1 | 20 | 20
> AS2 | 20 | 20
> AS3 | 60 | 60

> The selection algorithm used by the NameServer guarantees that AS1 and AS2 are each selected 20% of the time and AS3 is selected 60% of the time. Thus, if the sum of weight factors for all Unified Broker instances that support the same application adds up to 100, each weight factor specifies the exact percentage of time that the NameServer selects the given Unified Broker instance over time.

> ##### Arbitrary sum weight factors

> You can specify arbitrary weight factors as any sum of values (not necessarily 100), but the weight of each is always proportional to the sum, as shown in Table E–2.

> Table E–2: Weight factors based on arbitrary sums
> Unified Broker name | Weight factor | Percent of time selected
> --- | --- | ---
> AS1 | 2 | 2/7
> AS2 | 2 | 2/7
> AS3 | 3 | 3/7

> ##### Fail-over weight factor

> You can also specify a fail-over weight factor of zero (0) for a Unified Broker instance that you want to accept connection requests when the NameServer finds no other Unified Broker instance available in the pool.

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