Clear DefinitionsGas Limit
Pronunciation
[gas lim-it]
Analogy
A gas limit is like setting the maximum budget for a contractor's job. You're saying, 'You can spend up to this amount to complete the work, but not a penny more.' If the job can't be completed within that budget, the work stops and you're still charged for the resources used up to that point.
Definition
The maximum amount of computational work, measured in gas units, that a user is willing to pay for when executing a transaction or smart contract on Ethereum and compatible blockchains. The gas limit sets a ceiling on resource consumption to protect users from unexpectedly high fees.
Key Points Intro
Gas limits provide predictability and protection against excessive computational costs.
Key Points
Set by the user when submitting a transaction.
Protects against infinite loops and unexpectedly expensive operations.
If a transaction exceeds its gas limit, it fails but still incurs fees for resources consumed.
Must be set high enough to complete the intended operation.
Example
When deploying a complex smart contract on Ethereum, you might set a gas limit of 3 million gas units based on the estimated requirement of 2.5 million, giving yourself a safety buffer in case your estimation was slightly off.
Technical Deep Dive
The Ethereum Virtual Machine tracks gas consumption during execution by assigning a specific cost to each operation (opcode). Simple operations like addition cost 3 gas, while storage operations are more expensive at 20,000+ gas for a new storage slot. When a transaction's cumulative gas consumption reaches the specified limit, execution immediately halts with an 'out of gas' exception. The state is reverted to what it was before the transaction began, but the gas consumed is not refunded—it's paid to validators as compensation for the computational work performed. Blocks themselves also have gas limits, currently around 30 million on Ethereum, which cap the total computation per block.
Security Warning
Setting a gas limit too low risks transaction failure after consuming gas, resulting in wasted fees. However, setting it unnecessarily high can expose you to excessive costs if there's a bug in the contract that causes it to use more gas than expected.
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