pyth-network_pyth-crosschain/apps/developer-hub/content/docs/entropy/set-custom-gas-limits.mdx

---
title: Set Custom Gas Limits
description: How to set custom gas limits for Entropy callbacks
---

import { Step, Steps } from "fumadocs-ui/components/steps";
import { DynamicCodeBlock } from "fumadocs-ui/components/dynamic-codeblock";

Custom gas limits are useful when your callback function requires more gas than the [default provider limit]TODO(../contract-addresses), or when you want to optimize gas costs for simpler callbacks.

## Prerequisites

Before following this guide, you should first complete the basic setup from the [Generate Random Numbers in EVM Contracts](./generate-random-numbers-evm.mdx) guide. This guide builds upon that foundation and assumes you have:

- Installed the Pyth Entropy Solidity SDK
- Set up your contract with the `IEntropyConsumer` interface
- Implemented the basic `entropyCallback` function

## When to Use Custom Gas Limits

You might need custom gas limits in these scenarios:

- **Complex callback logic**: Your `entropyCallback` function performs computationally expensive operations
- **Gas optimization**: You want to use less gas for simple callbacks to reduce fees
- **Multiple operations**: Your callback needs to perform multiple state changes or external calls
- **Integration requirements**: Your application has specific gas requirements for reliability

## Implementation

### 1. Use requestV2 with Gas Limit Parameter

Instead of the basic `requestV2()` method, use the variant that accepts a `gasLimit` parameter:

<DynamicCodeBlock lang="solidity" 
code={`function requestRandomNumberWithCustomGas(
  uint32 customGasLimit
) external payable {
  // Calculate the fee for the custom gas limit
  uint256 fee = entropy.getFeeV2(customGasLimit);

// Request random number with custom gas limit
uint64 sequenceNumber = entropy.requestV2{ value: fee }(customGasLimit);

// Store the sequence number for tracking if needed
}
`} />

### 2. Calculate Fees with Custom Gas Limit

When using custom gas limits, you must use the `getFeeV2` variant that accepts a `gasLimit` parameter:

<DynamicCodeBlock lang="solidity" 
code={`// Get fee for custom gas limit
uint256 fee = entropy.getFeeV2(customGasLimit);

// NOT: uint256 fee = entropy.getFeeV2(); // This uses default gas limit
`} />

### 3. Complete Example

Here's a complete example showing how to implement custom gas limits:

<DynamicCodeBlock lang="solidity" 
code={`pragma solidity ^0.8.0;

import { IEntropyConsumer } from "@pythnetwork/entropy-sdk-solidity/IEntropyConsumer.sol";
import { IEntropyV2 } from "@pythnetwork/entropy-sdk-solidity/IEntropyV2.sol";

contract CustomGasLimitExample is IEntropyConsumer {
IEntropyV2 public entropy;
mapping(uint64 => bool) public processedRequests;

constructor(address entropyAddress) {
entropy = IEntropyV2(entropyAddress);
}

// Request with custom gas limit for complex callback
function requestComplexRandomNumber() external payable {
uint32 customGasLimit = 200000; // Higher limit for complex operations
uint256 fee = entropy.getFeeV2(customGasLimit);

    require(msg.value >= fee, "Insufficient fee");

    uint64 sequenceNumber = entropy.requestV2{ value: fee }(customGasLimit);
    // Store sequence number if needed for tracking

}

// Request with lower gas limit for simple callback
function requestSimpleRandomNumber() external payable {
uint32 customGasLimit = 50000; // Lower limit for simple operations
uint256 fee = entropy.getFeeV2(customGasLimit);

    require(msg.value >= fee, "Insufficient fee");

    uint64 sequenceNumber = entropy.requestV2{ value: fee }(customGasLimit);

}

// Complex callback that requires more gas
function entropyCallback(
uint64 sequenceNumber,
address provider,
bytes32 randomNumber
) internal override {
// Prevent duplicate processing
require(!processedRequests[sequenceNumber], "Already processed");
processedRequests[sequenceNumber] = true;

    // Complex operations that require more gas
    for (uint i = 0; i < 10; i++) {
      // Simulate complex state changes
      // This would require more gas than the default limit
    }

    // Use the random number for your application logic
    uint256 randomValue = uint256(randomNumber);
    // Your application logic here...

}

function getEntropy() internal view override returns (address) {
return address(entropy);
}
}
`} />

## Gas Limit Constraints

When setting custom gas limits, be aware of these constraints:

<Callout variant="info" header="Gas Limit Rules">
  Gas limits are automatically rounded up to the nearest multiple of **10,000**.
  Example: 19,000 becomes 20,000 25,500 becomes 30,000. The minimum gas limit is
  the provider's configured default limit. The maximum gas limit is 655,350,000
  (`uint16.max` \* 10,000).
</Callout>

### Recommended Gas Limits

- **Simple callbacks**: 50,000 - 100,000 gas
- **Moderate complexity**: 100,000 - 200,000 gas
- **Complex operations**: 200,000 - 500,000 gas
- **Very complex logic**: 500,000+ gas (use with caution)

## Best Practices

### 1. Estimate Gas Usage

Test your callback function to determine the actual gas usage:

<DynamicCodeBlock
  lang="solidity"
  code={`// In your tests, measure gas usage
uint256 gasStart = gasleft();
// Your callback logic here
uint256 gasUsed = gasStart - gasleft();
console.log("Gas used:", gasUsed);
`}
/>

### 2. Add Safety Buffer

Always add a safety buffer to your estimated gas usage:

<DynamicCodeBlock
  lang="solidity"
  code={`uint32 estimatedGas = 150000;
uint32 safetyBuffer = 20000;
uint32 customGasLimit = estimatedGas + safetyBuffer;
`}
/>

### 3. Handle Gas Limit Errors

Be prepared to handle cases where your gas limit is insufficient:

<Callout variant="warning">
  If your callback **runs out of gas**, the entropy provider will **not** be
  able to complete the callback. Always test your gas limits thoroughly and
  include adequate safety margins.
</Callout>

### 4. Consider Fee Implications

Higher gas limits result in higher fees. Balance your gas needs with cost considerations:

<DynamicCodeBlock
  lang="solidity"
  code={`// Compare fees for different gas limits
uint256 defaultFee = entropy.getFeeV2();
uint256 customFee = entropy.getFeeV2(customGasLimit);
uint256 additionalCost = customFee - defaultFee;
`}
/>

## Troubleshooting

If you're experiencing issues with custom gas limits:

1. **Callback not executing**: Your gas limit might be too low
2. **High fees**: Consider optimizing your callback or using a lower gas limit
3. **Reverts**: Check that your gas limit doesn't exceed the maximum allowed

For more debugging help, see the [Debug Callback Failures](/entropy/debug-callback-failures) guide.

## Additional Resources

- [Generate Random Numbers in EVM Contracts](/entropy/generate-random-numbers/evm) - Basic setup guide
- [Best Practices](/entropy/best-practices) - General optimization tips
- [Current Fees](/entropy/current-fees) - Fee information for different chains
- [Contract Addresses](/entropy/contract-addresses) - Entropy contract deployments