Execution Clients¶
The execution client is the half of an Ethereum node responsible for the work covered throughout most of this section so far: processing transactions, executing EVM bytecode, and maintaining the state trie. This chapter covers what it actually does and the major independent implementations.
What an execution client does¶
Given a block (handed to it by the consensus client), the execution client processes every transaction in order, running the EVM (see The EVM) for each one, updating account balances and contract storage, computing gas usage and fees, and producing the resulting new state root and transaction receipts. It also serves JSON-RPC requests, every eth_call, eth_getBalance, and similar query is answered by the execution client, since it's the component that actually holds and can query current state.
Major implementations¶
- Geth (go-ethereum): historically the most widely run execution client, written in Go, maintained by the Ethereum Foundation.
- Nethermind: written in C#/.NET.
- Besu: written in Java, notable for its enterprise and permissioned-network use cases in addition to public mainnet use.
- Erigon: a Geth-derived client focused specifically on faster sync times and more efficient storage for archive-node use cases (see Archive Nodes).
- Reth: a newer, Rust-based client developed by Paradigm, focused on performance and modularity.
Client diversity across these independent implementations is the specific structural benefit described in Ethereum Nodes, a bug specific to one client's code doesn't affect nodes running a different one, and the Ethereum community actively monitors the real-world distribution of which clients node operators actually run, historically raising concern when any single client's share has grown large enough to represent a meaningful systemic risk if it turned out to have a serious bug.
Common misconceptions¶
Different execution clients are not different, competing versions of Ethereum. They're independent implementations of the identical protocol specification, expected to (and, when working correctly, do) produce byte-for-byte identical results when processing the same blocks; the diversity is in the software, not in the rules being enforced.
An execution client alone cannot participate in Ethereum's consensus, since the Merge, it depends entirely on a paired consensus client (see Consensus Clients) to tell it which blocks to process and validate; it has no independent way to determine the canonical chain on its own.
Further reading¶
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