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76 lines
5.1 KiB
76 lines
5.1 KiB
---
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title: The Merge
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sort_key: A2
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---
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The Merge was probably the most significant upgrade to Ethereum since Homestead. This page explains what The Merge was
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and how it affected Geth users.
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## What was The Merge
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[The Merge](https://ethereum.org/en/upgrades/merge/) was an upgrade to Ethereum that swapped out its original
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proof-of-work (PoW) based consensus mechanism for a proof-of-stake based (PoS) mechanism. The term "Merge" refers
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to the fact that the initial phase of the transition involved launching a PoS chain in parallel with the
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PoW Ethereum Mainnet. That PoS chain, known as the Beacon Chain, was been executing the PoS consensus logic but
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without including any real Ethereum transaction data. The Merge was the moment when Ethereum's blockchain
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and the Beacon Chain joined together to form one unified chain. At the moment of The Merge, execution clients
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switched off their proof-of-work and block gossiping functions and handed responsibility for all consensus and
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fork choice logic over to consensus clients. This was a profound change to how Ethereum operates. Now that The Merge
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is done, node operators are required to run a consensus client in addition to an execution client such as Geth.
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## How did Geth change?
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Geth is an execution client. Historically, running an execution client alone was enough to turn a computer
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into a full Ethereum node. However, since The Merge, Geth has not been able to track the Ethereum chain on
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its own. Instead, it needs to be coupled to another piece of software called a ["consensus client"][con-client-link].
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The execution client is responsible for transaction handling, transaction gossip, state management and
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the Ethereum Virtual Machine (EVM). However, Geth is no longer responsible for block proposals or
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handling consensus logic. These are in the remit of the consensus client.
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There are five consensus clients available, all of which connect to Geth in the same way.
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Instructions for this are available on the [Consensus Clients page](/docs/interface/consensus-clients).
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## Client architecture
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The relationship between the two Ethereum clients is shown in the schematic below. The two clients each connect
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to their own respective peer-to-peer (P2P) networks. This is because the execution clients gossip transactions over
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their P2P network enabling them to manage their local mempool. The consensus clients gossip blocks over their P2P
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network, enabling consensus and chain growth.
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For this two-client structure to work, consensus clients must be able to pass bundles of transactions to Geth
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to be executed. Executing the transactions locally is how the client validates that the transactions do not
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violate any Ethereum rules and that the proposed update to Ethereum's state is correct. Likewise, when the node
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is selected to be a block producer the consensus client must be able to request executable data from Geth including bundles of transactions and metadata to
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include in the new block and a resulting state change. This inter-client communication is handled by a local RPC
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connection using the [`engine` API][engine-api-link] which is part of the JSON-RPC API exposed by Geth.
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## Using Geth since The Merge
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Although The Merge was a profound change to Ethereum's underlying achitecture, there were minimal changes to how Geth
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users interact with Ethereum. At The Merge responsibility for consensus logic and block propagation were handed over to
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the consensus layer, but all of Geth’s other functionality remains intact. This means transactions, contract deployments
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and data queries can still be handled by Geth using the same methods as before. This includes interacting with Geth using
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the JSON_RPC_API directly using tools such as [curl](https//curl.se), third party libraries such as
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[Web3.js][web3js-link] or [Web3.py][web3py-link] in development frameworks, e.g. [Truffle][truffle-link], [Hardhat][hardhat-link],
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[Brownie][brownie-link], [Foundry][foundry-link] or using Web3.js in Geth's built-in Javascript console.
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Much more information about the Javascript console is available on the [Javascript Console page](/docs/interface/javascript-console).
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## Summary
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The Merge was an upgrade to Ethereum that swapped the original PoW based consensus mechanism for a PoS based consensus
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mechanism. This changed the client software organization for Ethereum nodes. Since The Merge, both execution and consensus
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clients are required. Each client has responsibility for specific parts of the Ethereum protocol and communicate with each
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other over a local RPC connection.
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[engine-api-link]: https://github.com/ethereum/execution-apis/blob/main/src/engine/specification.md
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[cl-list]: https://ethereum.org/en/developers/docs/nodes-and-clients/#consensus-clients
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[web3py-link]: https://web3py.readthedocs.io/en/stable/web3.main.html
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[web3js-link]: https://web3js.readthedocs.io/en/v1.2.9/
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[brownie-link]: https://eth-brownie.readthedocs.io/en/stable/
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[truffle-link]: https://trufflesuite.com/
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[hardhat-link]: https://hardhat.org/
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[foundry-link]: https://github.com/foundry-rs/foundry)
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[con-client-link]:https://ethereum.org/en/glossary/#consensus-client
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