Roadmap › Blockchain & Web3 Fundamentals › Module: Ethereum in Depth
Lessons in this course (15)
10. Oracles, storage and indexing
IntermediateMediumLesson 10 of 15
- Oracles feed off-chain data (prices, weather, randomness) to contracts — Chainlink Data Feeds, Chainlink VRF (verifiable randomness), Pyth. Using a single DEX spot price as an oracle is a classic exploit vector (flash-loan price manipulation) — use time-weighted or decentralised feeds.
- Storage: on-chain storage is very expensive → store files on IPFS (content-addressed by hash — CID), pin with services (Pinata, web3.storage), or permanently on Arweave; store only the hash/URI on-chain.
- Indexing: reading historical events directly from nodes is slow → The Graph subgraphs, custom indexers listening to events into a SQL database, or APIs (Alchemy, Moralis, Etherscan).