Release 10.1A: OpenEdge Application Server:
Administration

> ## Understanding the NameServer’s load-balancing option

> Load balancing is a feature that allows client connection requests to be distributed, based on load, among multiple Unified broker instances that support the same Application Service. If your product includes load balancing (for example, the WebSpeed Enterprise Transaction Server) or you have installed the load-balancing option for a product that requires it (for example, the AppServer), 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, these weight factors give some sense of the amount of work that an individual WebSpeed Transaction Server instance can handle. For example, Table 9–3 shows the effect of weight factors specified for three WebSpeed Transaction Server instances registered for the same application service.

> Table 9–3: Weight factors based on percentage
> WebSpeed Transaction Server name | Weight factor | % of time selected
> --- | --- | ---
> WS1 | 20 | 20
> WS2 | 20 | 20
> WS3 | 60 | 60

> The selection algorithm used by the NameServer guarantees that WS1 and WS2 are each selected 20% of the time and WS3 is selected 60% of the time. Thus, if the sum of weight factors for all WebSpeed Transaction Server 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 WebSpeed Transaction Server instance over time.

> ##### Arbitrary weight factors

> You can specify any sum of values (not necessarily 100), but the weight of each is always proportional to the sum, as shown in Table 9–4.

> Table 9–4: Weight factors based on arbitrary sums
> WebSpeed Transaction Server name | Weight factor | % of time selected
> --- | --- | ---
> WS1 | 2 | 2/7
> WS2 | 2 | 2/7
> WS3 | 3 | 3/7

> ##### Fail-over weight factor

> Another use of Weight Factors is to provide connection-level fault tolerance, by keeping a backup Transaction Server ready to take over the load if the other Transaction Servers in your network fail. If you assign a Weight Factor of zero to the backup Transaction Server, the NameServer does not select it to fill any of the incoming Web requests. If the NameServer loses connection with all the other Transaction Servers that support the application service, the NameServer directs all the Web requests to the backup Transaction Server.

> For more information on load balancing and fault tolerance, see OpenEdge Getting Started: Installation and Configuration .

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