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Solana Sysvar Cluster Data

Solana 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.

There are two ways for a program to access a sysvar.

The first is to query the sysvar at runtime via the sysvar's get() function:

let clock = Clock::get()

The following sysvars support get:

  • Clock
  • EpochSchedule
  • Fees
  • Rent
  • EpochRewards

The second is to pass the sysvar to the program as an account by including its address as one of the accounts in the Instruction and then deserializing the data during execution. Access to sysvars accounts is always readonly.

let clock_sysvar_info = next_account_info(account_info_iter)?;
let clock = Clock::from_account_info(&clock_sysvar_info)?;

The first method is more efficient and does not require that the sysvar account be passed to the program, or specified in the Instruction the program is processing.

Clock​

The Clock sysvar contains data on cluster time, including the current slot, epoch, and estimated wall-clock Unix timestamp. It is updated every slot.

  • Address: SysvarC1ock11111111111111111111111111111111

  • Layout: Clock

  • Fields:

    • 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%.

EpochSchedule​

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 leader schedule)

  • Address: SysvarEpochSchedu1e111111111111111111111111
  • Layout: EpochSchedule

Fees​

The Fees sysvar contains the fee calculator for the current slot. It is updated every slot, based on the fee-rate governor.

  • Address: SysvarFees111111111111111111111111111111111
  • Layout: Fees

Instructions​

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. Read more information on instruction introspection.

  • Address: Sysvar1nstructions1111111111111111111111111
  • Layout: Instructions

RecentBlockhashes​

The RecentBlockhashes sysvar contains the active recent blockhashes as well as their associated fee calculators. It is updated every slot. Entries are ordered by descending block height, so the first entry holds the most recent block hash, and the last entry holds an old block hash.

Rent​

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.

  • Address: SysvarRent111111111111111111111111111111111
  • Layout: Rent

SlotHashes​

The SlotHashes sysvar contains the most recent hashes of the slot's parent banks. It is updated every slot.

  • Address: SysvarS1otHashes111111111111111111111111111
  • Layout: SlotHashes

SlotHistory​

The SlotHistory sysvar contains a bitvector of slots present over the last epoch. It is updated every slot.

  • Address: SysvarS1otHistory11111111111111111111111111
  • Layout: SlotHistory

StakeHistory​

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.

  • Address: SysvarStakeHistory1111111111111111111111111
  • Layout: StakeHistory

EpochRewards​

The EpochRewards sysvar tracks the progress of epoch rewards distribution. The sysvar is created in the first block of the epoch, and lasts for several blocks while paying out the rewards. When all rewards have been distributed, the sysvar is deleted. Unlike other sysvars, which almost always exist on-chain, EpochRewards sysvar only exists during the reward period. Therefore, calling EpochRewards::get() on blocks that are outside of the reward period will return an error, i.e. UnsupportedSysvar. This can serve as a method for determining whether epoch rewards distribution has finished.

  • Address: SysvarEpochRewards1111111111111111111111111
  • Layout: EpochRewards

LastRestartSlot​

The LastRestartSlot sysvar contains the slot number of the last restart or 0 (zero) if none ever happened.

  • Address: SysvarLastRestartS1ot1111111111111111111111
  • Layout: LastRestartSlot