This living document is a non-exhaustive list of key terms to understand the eth2 protocol, as defined by the Bison Trails Protocol Ops Team. Want to learn more? Check out the Bison Trails guide to eth2.
On eth2, the active set includes all validators with balance greater than 32 ETH.
On eth2, the primary source of load on the Beacon Chain will be "attestations." Attestations are availability votes for a shard block and, simultaneously, proof of stake votes for a beacon block. A sufficient number of attestations for the same shard block will create a "crosslink" which confirms the shard segment up to that shard block into the Beacon Chain.
eth2's Casper FFG stands for Casper, the Friendly Finality Gadget. This makes the final decision on which blocks are and are not a part of the chain.
A committee on eth2 is a subset of randomly selected validators, designated per slot, in which the first member of the committee has the chance to propose a block and all others must attest to it. The minimum committee size that the protocol targets is 128 attesters, and the maximum is ~5,000. As the active validator set increases, so will the number of committees. There can be 64 committees per slot, at maximum.
A smart contract on the Ethereum 1.X chain to which users can deposit chunks of 32 ETH to create validators on the eth2 chain The deposit contract went live on November 4th, 2020. You can track the activity related to it here.
The amount of ETH that is actually actively participating in consensus in an eth2 validator, equal to 32 ETH. Because validator balances change every epoch, it is very computationally expensive to continuously use new balances. The effective balance is just the validator balance, but rounded (in a special way) to a whole ETH number. Even if a validator accrues 2 ETH from rewards on the validator, bringing the validator balance to 34 ETH, only 32 ETH will be actively participating.
An epoch is the main time-measurement unit in eth2. Each epoch is composed of 32 slots in which blocks can be proposed. An epoch corresponds to ~6.4 minutes.
A state the chain achieves, when a block (and its contents—e.g. transactions) can no longer be changed without a large percentage of stake getting destroyed. eth2 guarantees finality, with a target of two epochs to reach it, at any given point in time. In order for finality to be reached, ⅔ of active validators need to get their attestations included on-chain.
Hysteresis is the rounding factor that impacts the validator balance to give the effective balance. The final settings are that once the validator balance falls by .25ETH below a whole number (i.e., 32 ETH -> 31.75 ETH) the effective balance goes from 32 ETH to 31 ETH. In order to bring it back up to 32, the validators balance needs to be 1.25 ETH above the whole number (i.e., once the validator balance hits 32.25 ETH, the effective balance goes from 31 to 32 ETH).
The Inactivity Leak Penalty is a countermeasure for if the network stops finalizing blocks due to a large number of validators going offline simultaneously.
LMD GHOST stands for Last Message Driven Greediest Heaviest Observed SubTree. This is the module that adds new blocks and decides what the head of the chain is.
A slot is a period of time in which a block proposer in eth2 may propose a block. This is the most granular measurement of “on-chain” time.
A validator client is a node that holds validators. It can technically also simultaneously serve as a beacon node, but this is not advisable because then it will be at risk of DoS attacks. The validator client will connect to public-facing beacon nodes to enable its validators to participate in consensus.
A validator is an entity actually participating in consensus using 32 ETH deposits. Each is primarily identified by a public_key and validator_index.
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