Selector ​

Introduction ​

What is the Selector? As its name suggests, it allows users to select specific items from a given namespace and context. There is a related trait, also named Selector, whose definition can be found below.

There is a specific scenario in Metasrv service. When a request to create a table is sent to the Metasrv service, it creates a routing table (the details of table creation will not be described here). The Metasrv service needs to select the appropriate Datanode list when creating a routing table.

Selector Type ​

Currently, there are two types of Selector available in the Metasrv service: LeasebasedSelector and LoadBasedSelector.

LeasebasedSelector [not recommended] ​

LeasebasedSelector is just a simple implementation of Selector, but it is not recommended.

It shuffles available Datanodes, and returns the list.

LoadBasedSelector ​

LoadBasedSelector is another implementation of the Selector.

It sorts available Datanodes according to the load, and returns a sorted list of these Datanodes.

Configuration ​

You can configure the Selector when starting the Metasrv service, with the default being LoadBasedSelector.

For example:

cargo run -- metasrv start --selector load_based

cargo run -- metasrv start --selector load_based

cargo run -- metasrv start --selector lease_based

cargo run -- metasrv start --selector lease_based