solana/book/src/stake-delegation-and-rewards.md

Stake Delegation and Rewards

Stakers are rewarded for helping validate the ledger. They do it by delegating their stake to fullnodes. Those fullnodes do the legwork and send votes to the stakers' staking accounts. The rest of the cluster uses those stake-weighted votes to select a block when forks arise. Both the fullnode and staker need some economic incentive to play their part. The fullnode needs to be compensated for its hardware and the staker needs to be compensated for risking getting its stake slashed. The economics are covered in staking rewards. This chapter, on the other hand, describes the underlying mechanics of its implementation.

Vote and Rewards accounts

The rewards process is split into two on-chain programs. The Vote program solves the problem of making stakes slashable. The Rewards account acts as custodian of the rewards pool. It is responsible for paying out each staker once the staker proves to the Rewards program that it participated in validating the ledger.

The Vote account contains the following state information:

• votes - The submitted votes.

• delegate_id - An identity that may operate with the weight of this account's stake. It is typically the identity of a fullnode, but may be any identity involved in stake-weighted computations.

• authorized_voter_id - Only this identity is authorized to submit votes.

• credits - The amount of unclaimed rewards.

• root_slot - The last slot to reach the full lockout commitment necessary for rewards.

The Rewards program is stateless and pays out reward when a staker submits its Vote account to the program. Claiming a reward requires a transaction that includes the following instructions:

1. RewardsInstruction::RedeemVoteCredits
2. VoteInstruction::ClearCredits

The Rewards program transfers lamports from the Rewards account to the Vote account's public key. The Rewards program also ensures that the ClearCredits instruction follows the RedeemVoteCredits instruction, such that a staker may not claim rewards for the same work more than once.

Delegating Stake

VoteInstruction::DelegateStake allows the staker to choose a fullnode to validate the ledger on its behalf. By being a delegate, the fullnode is entitled to collect transaction fees when its is leader. The larger the stake, the more often the fullnode will be able to collect those fees.

Authorizing a Vote Signer

VoteInstruction::AuthorizeVoter allows a staker to choose a signing service for its votes. That service is responsible for ensuring the vote won't cause the staker to be slashed.

Limitations

Many stakers may delegate their stakes to the same fullnode. The fullnode must send a separate vote to each staking account. If there are far more stakers than fullnodes, that's a lot of network traffic. An alternative design might have fullnodes submit each vote to just one account and then have each staker submit that account along with their own to collect its reward.