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Core Protocol

Alpenglow

A next-generation consensus protocol proposed in SIMD-0326 that aims to collapse Solana's legacy systems (Proof of History, Tower BFT, gossip-based vote propagation) into two streamlined mechanisms: Rotor for data propagation and Votor for off-chain voting. Alpenglow targets reducing transaction finality from ~12.8 seconds to under 150 milliseconds, representing the most significant consensus overhaul in Solana's history.

IDalpenglowAliasSIMD-326
Plain meaning

Plain meaning

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A next-generation consensus protocol proposed in SIMD-0326 that aims to collapse Solana's legacy systems (Proof of History, Tower BFT, gossip-based vote propagation) into two streamlined mechanisms: Rotor for data propagation and Votor for off-chain voting. Alpenglow targets reducing transaction finality from ~12.8 seconds to under 150 milliseconds, representing the most significant consensus overhaul in Solana's history.

Mental model

Mental model

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Technical context

Technical context

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Consensus, leader rotation, slots, epochs, and the runtime.

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Alpenglow (alpenglow)
Category: Core Protocol
Definition: A next-generation consensus protocol proposed in SIMD-0326 that aims to collapse Solana's legacy systems (Proof of History, Tower BFT, gossip-based vote propagation) into two streamlined mechanisms: Rotor for data propagation and Votor for off-chain voting. Alpenglow targets reducing transaction finality from ~12.8 seconds to under 150 milliseconds, representing the most significant consensus overhaul in Solana's history.
Aliases: SIMD-326
Related: Consensus Mechanism, Finality, Tower BFT, Proof of History (PoH)
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Branch

Consensus Mechanism

The protocol by which nodes in a distributed network agree on the current state of the ledger. Common mechanisms include Proof of Work (Bitcoin), Proof of Stake (Ethereum, Solana), and BFT variants. Consensus ensures all honest nodes converge on the same transaction history despite potential network delays or malicious actors.

Proof of Stake (PoS)Proof of Work (PoW)
Open term
Branch

Finality

The guarantee that a transaction cannot be reversed. Solana offers two levels: optimistic confirmation (~400ms, 66.7%+ stake voted) and full finality (~12-13 seconds, 31+ confirmations rooted). Once a slot is rooted, its transactions are irreversible under the assumption that no more than 1/3 of stake is malicious.

ConfirmationOptimistic Confirmation
Open term
Branch

Tower BFT

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).

Vote AccountFork
Open term
Branch

Proof of History (PoH)

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.

SlotLeader Schedule
Open term
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Blockchain General

Consensus Mechanism

The protocol by which nodes in a distributed network agree on the current state of the ledger. Common mechanisms include Proof of Work (Bitcoin), Proof of Stake (Ethereum, Solana), and BFT variants. Consensus ensures all honest nodes converge on the same transaction history despite potential network delays or malicious actors.

Open term
Core Protocol

Finality

The guarantee that a transaction cannot be reversed. Solana offers two levels: optimistic confirmation (~400ms, 66.7%+ stake voted) and full finality (~12-13 seconds, 31+ confirmations rooted). Once a slot is rooted, its transactions are irreversible under the assumption that no more than 1/3 of stake is malicious.

Open term
Core Protocol

Tower BFT

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).

Open term
Core Protocol

Proof of History (PoH)

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.

Open term
Commonly confused with

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Core Protocolalpenglow-certificate

Alpenglow Certificate

A fast finality certificate produced by the Alpenglow consensus protocol when a supermajority of validators (66.7%+ of stake) have attested to a block through Votor's off-chain voting mechanism. Once an Alpenglow certificate is formed, the block is considered final, reducing finality time from Tower BFT's ~12.8 seconds to a target of under 150 milliseconds. Certificates are compact proofs of consensus that can be verified by any node.

Open term
Core Protocolaccounts-db

AccountsDB

The persistent storage layer for all Solana accounts. AccountsDB stores account data in memory-mapped AppendVec files, indexed by pubkey and slot. It supports fast lookups, handles account deduplication across slots, and periodically cleans up dead accounts. AccountsDB is the largest consumer of validator disk space.

AliasAccountsDb
Open term
Core Protocolagave

Agave

The Rust-based Solana validator client maintained by Anza (formerly Solana Labs). Agave is the original and most widely deployed validator implementation. It handles all aspects of validation: TPU, TVU, gossip, AccountsDB, and RPC. The name 'Agave' was adopted to distinguish it from the Firedancer client.

AliasAnza Agave
Open term
Related terms

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Blockchain Generalconsensus

Consensus Mechanism

The protocol by which nodes in a distributed network agree on the current state of the ledger. Common mechanisms include Proof of Work (Bitcoin), Proof of Stake (Ethereum, Solana), and BFT variants. Consensus ensures all honest nodes converge on the same transaction history despite potential network delays or malicious actors.

Open term
Core Protocolfinality

Finality

The guarantee that a transaction cannot be reversed. Solana offers two levels: optimistic confirmation (~400ms, 66.7%+ stake voted) and full finality (~12-13 seconds, 31+ confirmations rooted). Once a slot is rooted, its transactions are irreversible under the assumption that no more than 1/3 of stake is malicious.

Open term
Core Protocoltower-bft

Tower BFT

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).

Open term
Core Protocolproof-of-history

Proof of History (PoH)

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.

Open term
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Core Protocol

Proof of History (PoH)

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.

Open term
Core Protocol

Tower BFT

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).

Open term
Core Protocol

Slot

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.

Open term
Core Protocol

Block

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.

Open term