Overview

Introduction

Datanode is mainly responsible for storing the actual data for GreptimeDB. As we know, in GreptimeDB, a table can have one or more regions, and Datanode is responsible for managing the reading and writing of these regions. Datanode is not aware of table and can be considered as a region server. Therefore, Frontend and Metasrv operate Datanode at the granularity of region.

Components

A Datanode contains all the components needed for a region server. Here we list some of the vital parts:

• A gRPC service is provided for reading and writing region data, and Frontend uses this service to read and write data from Datanodes.
• An HTTP service, through which you can obtain metrics, configuration information, etc., of the current node.
• Heartbeat Task is used to send heartbeat to the Metasrv. The heartbeat plays a crucial role in the distributed architecture of GreptimeDB and serves as a basic communication channel for distributed coordination. The upstream heartbeat messages contain important information such as the workload of a Region. If the Metasrv has made scheduling(such as Region migration) decisions, it will send instructions to the Datanode via downstream heartbeat messages.
• The Datanode does not include components like the Physical Planner, Optimizer, etc. (these are placed in the Frontend). The user's query requests for one or more Tables will be transformed into Region query requests in the Frontend. The Datanode is responsible for handling these Region query requests.
• A Region Manager is used to manage all Regions on a Datanode.
• GreptimeDB supports a pluggable multi-engine architecture, with existing engines including File Engine and Mito Engine.