The TVU component that replays received blocks by re-executing all transactions against the bank state. Replay stage verifies that transaction results match the leader's claimed results, updates the bank, and generates Tower BFT votes for valid blocks. If a replayed block is invalid, the validator marks that fork as dead.
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The TVU component that replays received blocks by re-executing all transactions against the bank state. Replay stage verifies that transaction results match the leader's claimed results, updates the bank, and generates Tower BFT votes for valid blocks. If a replayed block is invalid, the validator marks that fork as dead.
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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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Replay Stage (replay-stage) Category: Core Protocol Definition: The TVU component that replays received blocks by re-executing all transactions against the bank state. Replay stage verifies that transaction results match the leader's claimed results, updates the bank, and generates Tower BFT votes for valid blocks. If a replayed block is invalid, the validator marks that fork as dead. Related: TVU (Transaction Validation Unit), Bank, Fork
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Transaction Validation Unit—the pipeline on non-leader validators that receives shreds, reconstructs blocks, and replays transactions. TVU stages include: shred-fetch, retransmit, replay (execute transactions and verify results), and vote (submit Tower BFT votes). TVU runs continuously on all validators.
An in-memory representation of the accounts state at a specific slot. Each slot gets its own Bank that inherits from its parent slot's Bank. The Bank processes transactions, updates account balances, and tracks execution results. Once a slot is complete, the Bank is frozen and can be snapshotted or used as a parent for the next Bank.
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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Transaction Validation Unit—the pipeline on non-leader validators that receives shreds, reconstructs blocks, and replays transactions. TVU stages include: shred-fetch, retransmit, replay (execute transactions and verify results), and vote (submit Tower BFT votes). TVU runs continuously on all validators.
An in-memory representation of the accounts state at a specific slot. Each slot gets its own Bank that inherits from its parent slot's Bank. The Bank processes transactions, updates account balances, and tracks execution results. Once a slot is complete, the Bank is frozen and can be snapshotted or used as a parent for the next Bank.
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 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.