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 meta service. When a request to create a table is sent to the meta service, it creates a routing table (the details of table creation will not be described here). The meta 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 meta service: LeasebasedSelector and LoadBasedSelector.

LeasebasedSelector [not recommended]

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

It sorts available datanodes according to their lease time, and returns a sorted list of these datanodes.

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 meta service, with the default being LoadBasedSelector.

For example:

shell

cargo run -- metasrv start --selector LoadBased

shell

cargo run -- metasrv start --selector LeaseBased