EVM 与燃料机制

Ethereum isn't just a ledger; it's a decentralized computer! This "computer" is called the Ethereum Virtual Machine (EVM).

Think of the EVM as a global, single-instance computer that runs all smart contracts and updates the state of the blockchain.

Every node in the Ethereum network runs the EVM, ensuring everyone agrees on the exact state of the network.

The EVM is a deterministic state machine. This means that given the same starting state and the same transaction, it will always produce the same output state.

It processes transactions, executes smart contract code, and updates the blockchain's state (account balances, contract storage, etc.) accordingly.

This determinism is crucial for a decentralized network, as it allows all participants to independently verify the blockchain's integrity.

Smart contracts, written in languages like Solidity, are compiled into EVM bytecode. This bytecode consists of low-level instructions called opcodes.

Each opcode performs a specific task, such as adding two numbers, pushing data onto the stack, or storing data in memory.

The EVM executes these opcodes sequentially, processing the logic defined by the smart contract.

Running computations on a global, decentralized computer isn't free. This is where Gas comes in.

Gas is a unit of computational effort required to perform operations on the Ethereum network.

It's used to:

• Prevent infinite loops in smart contracts.
• Compensate miners/validators for their computational resources.
• Prioritize transactions based on the fee offered.

When you send a transaction, you specify a Gas Limit. This is the maximum amount of gas you're willing to spend on that transaction.

It acts as a safety mechanism. If the transaction requires more gas than the limit, it will revert (fail), but you still pay for the gas used up to that point.

A standard Ether transfer typically costs 21,000 gas units. Smart contract interactions can cost much more depending on their complexity.

While Gas Limit is the quantity, Gas Price is the cost per unit of gas. It's typically denominated in Gwei.

1 Gwei = 0.000000001 Ether. So, 1 Ether = 1,000,000,000 Gwei.

You can set a higher Gas Price to incentivize miners/validators to include your transaction in a block sooner, especially during network congestion.

The total transaction fee you pay is calculated as:

Gas Units Used * Gas Price

For example, if a transaction uses 21,000 gas units and the gas price is 50 Gwei:

• Fee = 21,000 * 50 Gwei = 1,050,000 Gwei
• Which is 0.00105 Ether

Remember, you only pay for the gas actually used, up to your Gas Limit.

If your transaction runs out of gas before completing its execution, it will result in an "Out of Gas" error.

When this happens:

• All state changes made by the transaction are reverted.
• The transaction fails and is not recorded on the blockchain (except as a failed transaction).
• Crucially, you still pay the transaction fee for all the gas consumed up to the point of failure.

Ethereum offers gas refunds for certain operations that reduce the blockchain's state size.

For instance, if a smart contract deletes data from storage, a portion of the gas spent on that deletion is refunded.

This incentivizes developers to write efficient contracts that don't unnecessarily bloat the blockchain's state.

Test your understanding of the Ethereum Virtual Machine and Gas mechanics.

In this lesson, we explored the core mechanics of the Ethereum network:

• The Ethereum Virtual Machine (EVM) is the global, deterministic computer executing smart contracts.
• Gas is the unit of computational effort required for transactions.
• Gas Limit sets the maximum gas a transaction can consume.
• Gas Price (in Gwei) determines the cost per unit of gas.
• Total transaction fees are Gas Used * Gas Price.
• Running "out of gas" reverts the transaction but still consumes the spent gas.

Understanding these concepts is vital for developing efficient and cost-effective DApps!