The complete ordered history of all transactions processed by the Solana cluster. The ledger is composed of sequential blocks (one per slot), each containing entries of transactions ordered by PoH. Validators store the ledger locally in Blockstore, and warehouse nodes or Bigtable archives provide long-term historical access.
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The complete ordered history of all transactions processed by the Solana cluster. The ledger is composed of sequential blocks (one per slot), each containing entries of transactions ordered by PoH. Validators store the ledger locally in Blockstore, and warehouse nodes or Bigtable archives provide long-term historical access.
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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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Ledger (ledger) Category: Core Protocol Definition: The complete ordered history of all transactions processed by the Solana cluster. The ledger is composed of sequential blocks (one per slot), each containing entries of transactions ordered by PoH. Validators store the ledger locally in Blockstore, and warehouse nodes or Bigtable archives provide long-term historical access. Related: Blockstore, Block, Entry
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A RocksDB-based database that stores raw shreds and block metadata on the validator's disk. Blockstore indexes shreds by slot and shred index, enabling block reconstruction and historical queries. It is separate from AccountsDB—Blockstore holds the ledger history while AccountsDB holds the current state.
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.
An ordered unit within a block containing a mix of PoH ticks and transaction batches. Each entry includes a PoH hash, a count of hashes since the previous entry, and zero or more transactions. Entries without transactions are tick entries that advance the PoH clock; entries with transactions prove those transactions occurred between two points in time.
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A validator's on-chain attestation affirming that it has verified and replayed a specific block, recorded as a hash of the validator's state at that slot. Ledger votes are submitted as vote transactions to the Vote Program and form the basis of Tower BFT consensus. Each vote carries increasing lockout commitments that make fork-switching progressively more expensive.
The validator currently designated to produce blocks for a given slot, as determined by the leader schedule. The leader receives transactions via its TPU, orders them using Proof of History, executes them, and broadcasts the resulting block as shreds via Turbine. Each slot has exactly one assigned leader, and leaders rotate according to the stake-weighted schedule.
The period during which a Tower BFT vote prevents a validator from switching to a competing fork. Lockouts double with each consecutive confirmation: vote depth 1 = 2-slot lockout, depth 2 = 4 slots, etc. This exponential lockout makes it increasingly expensive for validators to change their vote, providing economic finality.
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A RocksDB-based database that stores raw shreds and block metadata on the validator's disk. Blockstore indexes shreds by slot and shred index, enabling block reconstruction and historical queries. It is separate from AccountsDB—Blockstore holds the ledger history while AccountsDB holds the current state.
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.
An ordered unit within a block containing a mix of PoH ticks and transaction batches. Each entry includes a PoH hash, a count of hashes since the previous entry, and zero or more transactions. Entries without transactions are tick entries that advance the PoH clock; entries with transactions prove those transactions occurred between two points in time.
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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.