Staking

Terra's Staking module inherits from Cosmos SDK's staking module. This document is a stub, and covers mainly important Terra-specific notes about how it is used.

The Staking module enables Terra's Proof-of-Stake functionality by requiring validators to bond Luna, the native staking asset.

Transitions

End Block

This section was taken from the official Cosmos SDK docs, and placed here for your convenience to understand the Staking module's parameters.

Each abci end block call, the operations to update queues and validator set changes are specified to execute.

Validator Set Changes

The staking validator set is updated during this process by state transitions that run at the end of every block. As a part of this process any updated validators are also returned back to Tendermint for inclusion in the Tendermint validator set which is responsible for validating Tendermint messages at the consensus layer. Operations are as following:

• the new validator set is taken as the top params.MaxValidators number of validators retrieved from the ValidatorsByPower index
• the previous validator set is compared with the new validator set:
  • missing validators begin unbonding and their Tokens are transferred from the BondedPool to the NotBondedPool ModuleAccount
  • new validators are instantly bonded and their Tokens are transferred from the NotBondedPool to the BondedPool ModuleAccount

In all cases, any validators leaving or entering the bonded validator set or changing balances and staying within the bonded validator set incur an update message which is passed back to Tendermint.

Queues

Within staking, certain state-transitions are not instantaneous but take place over a duration of time (typically the unbonding period). When these transitions are mature certain operations must take place in order to complete the state operation. This is achieved through the use of queues which are checked/processed at the end of each block.

Unbonding Validators

When a validator is kicked out of the bonded validator set (either through being jailed, or not having sufficient bonded tokens) it begins the unbonding process along with all its delegations begin unbonding (while still being delegated to this validator). At this point the validator is said to be an unbonding validator, whereby it will mature to become an "unbonded validator" after the unbonding period has passed.

Each block the validator queue is to be checked for mature unbonding validators (namely with a completion time <= current time). At this point any mature validators which do not have any delegations remaining are deleted from state. For all other mature unbonding validators that still have remaining delegations, the validator.Status is switched from sdk.Unbonding to sdk.Unbonded.

Unbonding Delegations

Complete the unbonding of all mature UnbondingDelegations.Entries within the UnbondingDelegations queue with the following procedure:

• transfer the balance coins to the delegator's wallet address
• remove the mature entry from UnbondingDelegation.Entries
• remove the UnbondingDelegation object from the store if there are no remaining entries.

Redelegations

Complete the unbonding of all mature Redelegation.Entries within the Redelegations queue with the following procedure:

• remove the mature entry from Redelegation.Entries
• remove the Redelegation object from the store if there are no remaining entries.

Parameters

The subspace for the Staking module is staking.

type Params struct {
    UnbondingTime time.Duration `json:"unbonding_time" yaml:"unbonding_time"`
    MaxValidators uint16        `json:"max_validators" yaml:"max_validators"`
    MaxEntries    uint16        `json:"max_entries" yaml:"max_entries"`
    BondDenom string `json:"bond_denom" yaml:"bond_denom"`
}

UnbondingTime

Time duration of unbonding, in nanoseconds.

• type: time.Duration
• default value: time.Hour * 24 * 7 * 3 (3 weeks)

MaxValidators

Maximum number of active validators.

• type: uint16
• default value: 100

MaxEntries

Max entries for either unbonding delegation or redelegation (per pair/trio). We need to be a bit careful about potential overflow here, since this is user-determined.

• type: uint16
• default value: 7

BondDenom

Defines the denomination of the asset required for staking.

• type: string
• default value: uluna