The most common use case for Data Feeds is to Get the Latest Price. However, AggregatorV3Interface also exposes functions which can be used to retrieve price data of a previous round ID.

There are two parameters that can cause Chainlink nodes to update:

You can find these parameters at data.chain.link on an example like ETH / USD.

To learn how data feeds update, see the Decentralized Data Model page.

Historical Rounds

As shown in the decentralized model, the consumer contracts call the proxy contract, which abstracts the underlying aggregator contract. The main advantage is to enable upgrades of the aggregator without impacting the consumer contracts. That also means that historical data can can be stored in different aggregators.
As show in the following sequence diagram, to get historical data, call the getRoundData function function and provide roundId as a parameter.

Note that roundIds have different meanings in proxy contracts and in aggregator contracts.

roundId in Aggregator (aggregatorRoundId)

Oracles provide periodic data updates to the aggregators. Data feeds are updated in rounds. Rounds are identified by their roundId, which increases with each new round. This increase may not be monotonic. Knowing the roundId of a previous round allows contracts to consume historical price data.

The examples in this document name the aggregator roundId as aggregatorRoundId to differentiate it from the proxy roundId.

roundId in Proxy

Because a proxy has references to current and all previous underlying aggregators, it needs a way to fetch data from the correct aggregator. The roundId is computed in the proxy contract as shown in the following example:

roundId = uint80((uint256(phaseId) << 64) | aggregatorRoundId);

where:

• phaseId is incremented each time the underlying aggregator implementation is updated. It is used as key to find the aggregator address.
• aggregatorRoundId is the aggregator roundId. The id starts at 1.
• roundId is the computed round id. From the above formula, you can think of it as a large number containing the phaseId and the aggregatorRoundId.

Example:

When you query historical data, it is important to know when you reach the end of the history of the underlying aggregator. As an example, if the latestRoundData function of the LINK / USD feed on Ethereum Mainnet returns roundId = 92233720368547771158, you can use this value to compute the phaseId and aggregatorRoundId:

• phaseId = 92233720368547771158 >> 64: Right shifting an integer by 64 bits is equivalent to dividing it by 2^64: phaseId = 92233720368547771158/ 2^64 = 5. The current phase id is 5 , which means that this proxy has had 5 underlying aggregators since its initial deployment.
• aggregatorRoundId = uint64(92233720368547771158): This retrieves the first 64 bits from the right. To calculate this off-chain, you can use the following JavaScript example:

// First parse to BigInt to perform computation with big integers
const num = BigInt("92233720368547771158");
const num2 = BigInt("0xFFFFFFFFFFFFFFFF"); // Largest 64bits integer

console.log(Number(num >> 64n)); // returns 5 (phaseId)
console.log(Number(num & num2)) // returns 13078 (aggregatorRoundId) . Use & (AND bitwise operator) which sets each bit to _1_ if both bits are _1_

Using 13078 as the current aggregator's round, get its historical data by looping over the getRoundData function:

• Start from the first round: 92233720368547758081 (result of 92233720368547771158 - 13078 + 1)
• Continue until the current round: 92233720368547771158

To get the historical data for previous aggregators, decrement the phaseId and start from round 1. For phase 4, get the starting roundId off-chain using the following JavaScript example:

const phaseId = BigInt("4");
const aggregatorRoundId = BigInt("1");

roundId = (phaseId << 64n) | aggregatorRoundId // returns 73786976294838206465n

Loop over the getRoundData function. Start at 73786976294838206465 and increment it until you get a revert. This means that you reached the last round for the underlying aggregator. The same process could be repeated for previous phaseIds (3,2,1).

getRoundData return values

The getRoundData function returns the following values:

• roundId: The combination of aggregatorRoundId and phaseId (see explanation above). The roundId can jump significantly when the phaseId is updated.
• answer is the price.
• answeredInRound: The combination of aggregatorAnsweredInRound and phaseId. aggregatorAnsweredInRound: The round the answer was updated in. You can check answeredInRound against the current roundId. If answeredInRound is less than roundId, the answer is being carried over. If answeredInRound is equal to roundId, then the answer is fresh.
• startedAt: The timestamp when the round started.
• updatedAt: The timestamp when the answer was computed.

Solidity

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.7;

import "@chainlink/contracts/src/v0.8/interfaces/AggregatorV3Interface.sol";

/**
 * THIS IS AN EXAMPLE CONTRACT THAT USES HARDCODED VALUES FOR CLARITY.
 * THIS IS AN EXAMPLE CONTRACT THAT USES UN-AUDITED CODE.
 * DO NOT USE THIS CODE IN PRODUCTION.
 */

contract HistoricalPriceConsumerV3 {

    AggregatorV3Interface internal priceFeed;

    /**
     * Network: Goerli
     * Aggregator: ETH/USD
     * Address: 0xD4a33860578De61DBAbDc8BFdb98FD742fA7028e
     */
    constructor() {
        priceFeed = AggregatorV3Interface(0xD4a33860578De61DBAbDc8BFdb98FD742fA7028e);
    }

    /**
     * Returns historical price for a round id.
     * roundId is NOT incremental. Not all roundIds are valid.
     * You must know a valid roundId before consuming historical data.
     *
     * ROUNDID VALUES:
     *    InValid:      18446744073709562300
     *    Valid:        18446744073709554683
     *
     * @dev A timestamp with zero value means the round is not complete and should not be used.
     */
    function getHistoricalPrice(uint80 roundId) public view returns (int256) {
        (
            uint80 id,
            int price,
            uint startedAt,
            uint timeStamp,
            uint80 answeredInRound
        ) = priceFeed.getRoundData(roundId);
        require(timeStamp > 0, "Round not complete");
        return price;
    }
}

Javascript

/**
 * THIS IS EXAMPLE CODE THAT USES HARDCODED VALUES FOR CLARITY.
 * THIS IS EXAMPLE CODE THAT USES UN-AUDITED CODE.
 * DO NOT USE THIS CODE IN PRODUCTION.
 */

const Web3 = require("web3") // for nodejs only
// Replace the provider URL with your own endpoint URL
const web3 = new Web3("https://rpc.ankr.com/eth_goerli")
const aggregatorV3InterfaceABI = [{ "inputs": [], "name": "decimals", "outputs": [{ "internalType": "uint8", "name": "", "type": "uint8" }], "stateMutability": "view", "type": "function" }, { "inputs": [], "name": "description", "outputs": [{ "internalType": "string", "name": "", "type": "string" }], "stateMutability": "view", "type": "function" }, { "inputs": [{ "internalType": "uint80", "name": "_roundId", "type": "uint80" }], "name": "getRoundData", "outputs": [{ "internalType": "uint80", "name": "roundId", "type": "uint80" }, { "internalType": "int256", "name": "answer", "type": "int256" }, { "internalType": "uint256", "name": "startedAt", "type": "uint256" }, { "internalType": "uint256", "name": "updatedAt", "type": "uint256" }, { "internalType": "uint80", "name": "answeredInRound", "type": "uint80" }], "stateMutability": "view", "type": "function" }, { "inputs": [], "name": "latestRoundData", "outputs": [{ "internalType": "uint80", "name": "roundId", "type": "uint80" }, { "internalType": "int256", "name": "answer", "type": "int256" }, { "internalType": "uint256", "name": "startedAt", "type": "uint256" }, { "internalType": "uint256", "name": "updatedAt", "type": "uint256" }, { "internalType": "uint80", "name": "answeredInRound", "type": "uint80" }], "stateMutability": "view", "type": "function" }, { "inputs": [], "name": "version", "outputs": [{ "internalType": "uint256", "name": "", "type": "uint256" }], "stateMutability": "view", "type": "function" }]
const addr = "0xA39434A63A52E749F02807ae27335515BA4b07F7"
const priceFeed = new web3.eth.Contract(aggregatorV3InterfaceABI, addr)

// Valid roundId must be known. They are NOT incremental.
let validId = BigInt("18446744073709554177")
priceFeed.methods.getRoundData(validId).call()
    .then((historicalRoundData) => {
        document.getElementById('get-price-field').value = historicalRoundData.answer
    })

Python

# THIS IS EXAMPLE CODE THAT USES HARDCODED VALUES FOR CLARITY.
# THIS IS EXAMPLE CODE THAT USES UN-AUDITED CODE.
# DO NOT USE THIS CODE IN PRODUCTION.

from web3 import Web3

# Change this to use your own RPC URL
web3 = Web3(Web3.HTTPProvider('https://rpc.ankr.com/eth_goerli'))
# AggregatorV3Interface ABI
abi = '[{"inputs":[],"name":"decimals","outputs":[{"internalType":"uint8","name":"","type":"uint8"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"description","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"uint80","name":"_roundId","type":"uint80"}],"name":"getRoundData","outputs":[{"internalType":"uint80","name":"roundId","type":"uint80"},{"internalType":"int256","name":"answer","type":"int256"},{"internalType":"uint256","name":"startedAt","type":"uint256"},{"internalType":"uint256","name":"updatedAt","type":"uint256"},{"internalType":"uint80","name":"answeredInRound","type":"uint80"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"latestRoundData","outputs":[{"internalType":"uint80","name":"roundId","type":"uint80"},{"internalType":"int256","name":"answer","type":"int256"},{"internalType":"uint256","name":"startedAt","type":"uint256"},{"internalType":"uint256","name":"updatedAt","type":"uint256"},{"internalType":"uint80","name":"answeredInRound","type":"uint80"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"version","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"}]'
# Price Feed address
addr = '0xA39434A63A52E749F02807ae27335515BA4b07F7'

# Set up contract instance
contract = web3.eth.contract(address=addr, abi=abi)

#  Valid roundId must be known. They are NOT incremental.
# invalidRoundId = 18446744073709562300
validRoundId = 18446744073709554177

historicalData = contract.functions.getRoundData(validRoundId).call()
print(historicalData)