Data indexing service
Because there's no server, every data of a DApp will be stored on blockchain. And keeping track of all those datas is too complicated if getting data directly from blockchain.
The Graph is a decentralized protocol for indexing and querying data from blockchains, starting with Ethereum. It makes it possible to query data that is difficult to query directly. Luckily, The Graph open-sourced their source code and build a Docker image so that every developers can run their own graph on any EVM-compatible network.
To start running your graph node:
docker-compose up -d
After that, a GraphQL playground will be served on port 8000.