Greedy Heaviest Observed Subtree
Web3 / blockchain technology
The GHOST protocol is a consensus mechanism variation of the longest-chain rule that Ethereum adopted to improve security and reduce uncle block waste. Rather than simply following the chain with the most blocks, GHOST considers the entire tree of valid blocks, including those that weren't included in the main chain (uncle blocks). When choosing between competing chains of equal length, GHOST selects the branch with the heaviest cumulative work, including all observed subtrees. This approach maintains security while significantly improving throughput by allowing legitimate blocks created by honest miners to contribute to chain weight even if they weren't directly included in the canonical chain. Example: Ethereum's Proof-of-Work era employed the GHOST rule until the merge to Proof-of-Stake in September 2022, where uncle blocks (renamed "ommer blocks") received partial rewards for contributing to network security even though they weren't part of the main chain. Why it matters for blockchain technology: GHOST substantially improves network efficiency and security by utilizing all valid work performed by honest miners, reducing wasted computational resources and strengthening consensus against certain attack vectors compared to pure longest-chain rules.
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