The algorithm validators use to decide which fork to build upon when multiple competing chains exist. Solana combines Tower BFT voting weight (stake-weighted votes with lockout) and a GHOST-like rule to select the fork with the heaviest cumulative stake support.
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The algorithm validators use to decide which fork to build upon when multiple competing chains exist. Solana combines Tower BFT voting weight (stake-weighted votes with lockout) and a GHOST-like rule to select the fork with the heaviest cumulative stake support.
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Think of it as part of the chain machinery that keeps ordering, execution, or consensus moving.
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Consensus, leader rotation, slots, epochs, and the runtime.
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Fork Choice (fork-choice) Category: Core Protocol Definition: The algorithm validators use to decide which fork to build upon when multiple competing chains exist. Solana combines Tower BFT voting weight (stake-weighted votes with lockout) and a GHOST-like rule to select the fork with the heaviest cumulative stake support. Related: Fork, Tower BFT, GHOST (Greedy Heaviest Observed SubTree)
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A divergence in the blockchain where two or more blocks are produced for the same slot or different validators build on different parent blocks. Forks are common during normal operation and are resolved by Tower BFT's fork-choice rule. Only one fork ultimately becomes the canonical chain; transactions on abandoned forks are dropped.
Solana's custom BFT consensus algorithm built on top of Proof of History. Tower BFT uses PoH as a clock to reduce communication overhead in traditional PBFT from O(n²) to O(n). Validators vote on forks with exponentially increasing lockout periods—each consecutive vote doubles the lockout, making rollbacks progressively more expensive. A fork is finalized when it reaches supermajority (66.7%+ of stake).
Greedy Heaviest Observed SubTree—a fork-choice rule where validators select the fork that has the most cumulative stake-weighted votes. Unlike longest-chain rules, GHOST considers all votes in the tree, not just the tip. Solana's implementation weighs votes by stake and factors in Tower BFT lockout periods.
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A divergence in the blockchain where two or more blocks are produced for the same slot or different validators build on different parent blocks. Forks are common during normal operation and are resolved by Tower BFT's fork-choice rule. Only one fork ultimately becomes the canonical chain; transactions on abandoned forks are dropped.
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A divergence in the blockchain where two or more blocks are produced for the same slot or different validators build on different parent blocks. Forks are common during normal operation and are resolved by Tower BFT's fork-choice rule. Only one fork ultimately becomes the canonical chain; transactions on abandoned forks are dropped.
Solana's custom BFT consensus algorithm built on top of Proof of History. Tower BFT uses PoH as a clock to reduce communication overhead in traditional PBFT from O(n²) to O(n). Validators vote on forks with exponentially increasing lockout periods—each consecutive vote doubles the lockout, making rollbacks progressively more expensive. A fork is finalized when it reaches supermajority (66.7%+ of stake).
Greedy Heaviest Observed SubTree—a fork-choice rule where validators select the fork that has the most cumulative stake-weighted votes. Unlike longest-chain rules, GHOST considers all votes in the tree, not just the tip. Solana's implementation weighs votes by stake and factors in Tower BFT lockout periods.
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A clock mechanism that cryptographically proves the passage of time between events. PoH uses a sequential SHA-256 hash chain where each output becomes the next input, creating a verifiable ordering of events without requiring consensus. The leader produces ~400,000 hashes per slot (~400ms), and any validator can verify the sequence in parallel, enabling Solana's high throughput by removing the need for validators to agree on time.
Solana's custom BFT consensus algorithm built on top of Proof of History. Tower BFT uses PoH as a clock to reduce communication overhead in traditional PBFT from O(n²) to O(n). Validators vote on forks with exponentially increasing lockout periods—each consecutive vote doubles the lockout, making rollbacks progressively more expensive. A fork is finalized when it reaches supermajority (66.7%+ of stake).
A time window during which a designated leader validator can produce a block. Each slot lasts approximately 400 milliseconds. Slots are numbered sequentially from genesis and grouped into epochs of 432,000 slots (~2-3 days). Not every slot produces a block—a skipped slot means the leader was offline or too slow.
A set of entries produced by a leader during a single slot. A block contains transactions bundled into entries, each with a PoH hash proving ordering. Blocks are broken into shreds for network propagation via Turbine. Maximum block size is limited by compute units (48M CU cap per block) rather than byte size.