Onchain Data & Indexing

Onchain Data & Indexing

What You Probably Got Wrong

You try to query historical state via RPC calls. You can't cheaply read past state. eth_call reads current state. Reading state at a historical block requires an archive node (expensive, slow). For historical data, you need an indexer.

You loop through blocks looking for events. Scanning millions of blocks with eth_getLogs is O(n) — it will timeout, get rate-limited, or cost a fortune in RPC credits. Use an indexer that has already processed every block.

You store query results onchain. Leaderboards, activity feeds, analytics — these belong offchain. Compute offchain, index events offchain. If you need an onchain commitment, store a hash.

You don't know about The Graph. The Graph turns your contract's events into a queryable GraphQL API. It's how every serious dApp reads historical data. Etherscan uses indexers. Uniswap uses indexers. So should you.

You treat events as optional. Events are THE primary way to read historical onchain activity. If your contract doesn't emit events, nobody can build a frontend, dashboard, or analytics on top of it. Design contracts event-first.

Events Are Your API

Solidity events are cheap to emit (~375 gas base + 375 per indexed topic + 8 gas per byte of data) and free to read offchain. They're stored in transaction receipts, not in contract storage, so they don't cost storage gas.

Design Contracts Event-First

Every state change should emit an event. This isn't just good practice — it's how your frontend, indexer, and block explorer know what happened.

// ✅ Good — every action emits a queryable event
contract Marketplace {
    event Listed(
        uint256 indexed listingId,
        address indexed seller,
        address indexed tokenContract,
        uint256 tokenId,
        uint256 price
    );
    event Sold(uint256 indexed listingId, address indexed buyer, uint256 price);
    event Cancelled(uint256 indexed listingId);

    function list(address token, uint256 tokenId, uint256 price) external {
        uint256 id = nextListingId++;
        listings[id] = Listing(msg.sender, token, tokenId, price, true);