Glossary

Network and timing

• Slot. The basic unit of time on Solana, targeted at about 400 milliseconds. One leader may produce one block per slot.
• Epoch. A period of 432,000 slots, roughly two to three days. Stake and the leader schedule are fixed per epoch.
• Leader. The validator scheduled to produce blocks in a given slot. Each leader produces four consecutive slots.
• Leader schedule. The publicly known list of leaders for every slot in an epoch, derived from stake.
• Skipped slot. A slot in which no block was produced or the block was not accepted by the network.
• Fork. A competing chain of blocks. Blocks on a minority fork are eventually abandoned.

Transactions

• Transaction. A signed message containing instructions. Its first signature uniquely identifies it.
• Wire format. The binary serialization of a transaction as sent over the network.
• Versioned transaction (v0). The current transaction format, which supports address lookup tables.
• Address lookup table (ALT). An on-chain table of addresses that lets a v0 transaction reference many accounts compactly.
• Recent blockhash. A hash included in every transaction to prove recency. It is valid for about 150 slots, roughly one minute.
• Compute units. The measure of computation a transaction consumes. The limit is set with the Compute Budget program.
• Priority fee. An additional fee per compute unit, set with the Compute Budget program, that makes a transaction more attractive to the leader.

Validator internals

• TPU (Transaction Processing Unit). The part of a validator that receives transactions, verifies signatures and executes them in its banking stage when it is the leader.
• QUIC. The transport protocol used to deliver transactions to the TPU.
• SWQoS (stake-weighted quality of service). The policy by which a leader allocates its QUIC connection capacity in proportion to the stake of the sending peer.
• Banking stage. The TPU stage that executes transactions and records them into entries.
• Entry. A batch of transactions recorded by the leader in order, chained by hashes.
• Shred. A fragment of the block, small enough to fit into a single network packet.
• Data shred / coding shred. Data shreds carry block data. Coding shreds carry erasure codes that allow missing data shreds to be recovered.
• FEC set. A group of data shreds together with the coding shreds that protect them.
• Turbine. The protocol that propagates shreds from the leader through a tree of validators.
• Replay. The process in which validators reassemble shreds into the block and re-execute it.

Commitment

• processed. The node has processed a block containing the transaction. It may still be rolled back.
• confirmed. A supermajority of stake has voted on the block.
• finalized. The block has been rooted and cannot be rolled back.

MEV

• MEV (maximal extractable value). Value that can be captured by including, excluding or ordering transactions.
• Searcher. A participant who looks for MEV opportunities and submits transactions to capture them.
• Backrun. A transaction placed after a target transaction to capture the opportunity that the target creates, for example a price difference after a large swap.
• Sandwich. Placing one transaction before and one after a target transaction to profit from its price impact.
• Bundle. A group of transactions that a block builder executes together and in order, or not at all.
• Relayer. A service that receives transactions on behalf of a validator and forwards them, for example to a block engine.
• Block engine. A service that receives transactions from relayers. With Private Orderflow over gRPC, your server takes this role.
• Scheduler priority. The order in which a leader's scheduler processes conflicting transactions, based on the fee it earns per unit of cost.
• Arbitrage. Capturing price differences between markets or pools.
• Liquidation. Closing an undercollateralized position in a lending protocol, usually for a reward.
• Landing rate. The share of submitted transactions that are included in a block.