Chapter 3 Load Balancing Algorithm - Placement Strategy

In Chapter 2, we introduced all the implementations of the LoadSheddingStrategy. In this chapter, we will delve into the implementation principles of the placement strategy and discuss the effects of combining different placement strategies with different LoadSheddingStrategy implementations. Ultimately, we will present a scoring table that allows readers to clearly see the strengths and weaknesses of different algorithm combinations.

The placement strategy is controlled by the configuration loadBalancerLoadPlacementStrategy, with the default being the LeastLongTermMessageRate strategy.

# load balance placement strategy, support LeastLongTermMessageRate and LeastResourceUsageWithWeight
loadBalancerLoadPlacementStrategy=org.apache.pulsar.broker.loadbalance.impl.LeastLongTermMessageRate

The implemented interface is named org.apache.pulsar.broker.loadbalance.ModularLoadManagerStrategy, and there are four implementations. Among them, RoundRobinBrokerSelector is usually not considered because it places bundles using a round robin method without considering key information such as load data. In the following sections, we will focus on the LeastLongTermMessageRate and LeastResourceUsageWithWeight implementations, while the content related to AvgShedder will be covered in the next chapter.