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Signing Info (Liveness)

Every block includes a set of precommits by the validators for the previous block, known as the LastCommitInfo provided by Tendermint. A LastCommitInfo is valid so long as it contains precommits from +2/3 of total voting power.

Proposers are incentivized to include precommits from all validators in the Tendermint LastCommitInfo by receiving additional fees proportional to the difference between the voting power included in the LastCommitInfo and +2/3 (see distribution).

type LastCommitInfo struct {
Round int32
Votes []VoteInfo

Validators are penalized for failing to be included in the LastCommitInfo for some number of blocks by being automatically jailed, potentially slashed, and unbonded.

Information about validator's liveness activity is tracked through ValidatorSigningInfo. It is indexed in the store as follows:

  • ValidatorSigningInfo: 0x01 | ConsAddrLen (1 byte) | ConsAddress -> ProtocolBuffer(ValSigningInfo)
  • MissedBlocksBitArray: 0x02 | ConsAddrLen (1 byte) | ConsAddress | LittleEndianUint64(signArrayIndex) -> VarInt(didMiss) (varint is a number encoding format)

The first mapping allows us to easily lookup the recent signing info for a validator based on the validator's consensus address.

The second mapping (MissedBlocksBitArray) acts as a bit-array of size SignedBlocksWindow that tells us if the validator missed the block for a given index in the bit-array. The index in the bit-array is given as little endian uint64. The result is a varint that takes on 0 or 1, where 0 indicates the validator did not miss (did sign) the corresponding block, and 1 indicates they missed the block (did not sign).

Note that the MissedBlocksBitArray is not explicitly initialized up-front. Keys are added as we progress through the first SignedBlocksWindow blocks for a newly bonded validator. The SignedBlocksWindow parameter defines the size (number of blocks) of the sliding window used to track validator liveness.

The information stored for tracking validator liveness is as follows: