Velas exposes a variety of cluster state data to programs via sysvar accounts. These accounts are populated at known addresses published along with the account layouts in the
solana-program crate, and outlined below.
To include sysvar data in program operations, pass the sysvar account address in the list of accounts in a transaction. The account can be read in your instruction processor like any other account. Access to sysvars accounts is always readonly.
The Clock sysvar contains data on cluster time, including the current slot, epoch, and estimated wall-clock Unix timestamp. It is updated every slot.
- Layout: Clock
slot: the current slot
epoch_start_timestamp: the Unix timestamp of the first slot in this epoch. In the first slot of an epoch, this timestamp is identical to the unix_timestamp (below).
epoch: the current epoch
leader_schedule_epoch: the most recent epoch for which the leader schedule has already been generated
unix_timestamp: the Unix timestamp of this slot. Each slot has an estimated duration based on Proof of History. But in reality, slots may elapse faster and slower than this estimate. As a result, the Unix timestamp of a slot is generated based on oracle input from voting validators. This timestamp is calculated as the stake-weighted median of timestamp estimates provided by votes, bounded by the expected time elapsed since the start of the epoch.
More explicitly: for each slot, the most recent vote timestamp provided by each validator is used to generate a timestamp estimate for the current slot (the elapsed slots since the vote timestamp are assumed to be Bank::ns_per_slot). Each timestamp estimate is associated with the stake delegated to that vote account to create a distribution of timestamps by stake. The median timestamp is used as the
unix_timestamp, unless the elapsed time since the
epoch_start_timestamp has deviated from the expected elapsed time by more than 25%.
The EpochSchedule sysvar contains epoch scheduling constants that are set in genesis, and enables calculating the number of slots in a given epoch, the epoch for a given slot, etc. (Note: the epoch schedule is distinct from the
- Layout: EpochSchedule
The Fees sysvar contains the fee calculator for the current slot. It is updated every slot, based on the fee-rate governor.
- Layout: Fees
The Instructions sysvar contains the serialized instructions in a Message while that Message is being processed. This allows program instructions to reference other instructions in the same transaction.
- Layout: Instructions
The RecentBlockhashes sysvar contains the active recent blockhashes as well as their associated fee calculators. It is updated every slot.
- Layout: RecentBlockhashes
The Rent sysvar contains the rental rate. Currently, the rate is static and set in genesis. The Rent burn percentage is modified by manual feature activation.
- Layout: Rent
The SlotHashes sysvar contains the most recent hashes of the slot's parent banks. It is updated every slot.
- Layout: SlotHashes
The SlotHistory sysvar contains a bitvector of slots present over the last epoch. It is updated every slot.
- Layout: SlotHistory
The StakeHistory sysvar contains the history of cluster-wide stake activations and de-activations per epoch. It is updated at the start of every epoch.
- Layout: StakeHistory