Why is Polygon a Commit Chain and not a side chain?

Is Polygon a side chain? You will know after reading this article.

Original: finematics

So what is a commit chain? How is it different from side chains? What makes Polygon Commit Chain a commit chain instead of a side chain? We will answer all these questions in this article.

Let’s start by understanding what exactly is a side chain.

Side chain

The side chain is essentially a separate blockchain that can be used as a way to extend the layer 1 blockchain (such as Ethereum or Bitcoin). As the name implies, the side chain runs in parallel with the main chain or runs on the “side” of the main chain.

The side chain has its own consensus mechanism, usually in the form of Proof of Stake (PoS), Delegated Proof of Stake (DPoS) or Proof of Authority (PoA).

The side chain allows users to send their tokens from the main chain and receive them on the side chain. Once the funds are transferred to the sidechain, they can be used in the sidechain ecosystem. Similarly, users can withdraw their tokens from the side chain to the main chain. The whole process is called two-way hook or two-way bridge. It should be noted that once user tokens are on the side chain, they are completely dependent on the consensus mechanism of the side chain.

Initially, all scaling solutions (such as side chains, Plasma, and Rollup) were classified as layer 2 solutions because they were built on top of layer 1.

Coin World-Why is Polygon a Commit Chain and not a side chain?

After a while, the Ethereum community began to distinguish between the extended solution that is fully protected by the Ethereum main chain-layer 2 and other extended options with its own consensus mechanism-the side chain. Currently, almost all scaling solutions are classified as one or the other.

When it comes to Polygon Commit Chain, it is worth distinguishing it from side chains because it has many additional capabilities that rely on the security of the main Ethereum layer.

Let us review them one by one.

Permissionless validator on Ethereum

Many side chains use consensus mechanisms to limit the number of entities that can verify the chain. For example, in Delegated Proof of Stake (DPoS), there are usually 21 validators selected by token holders, and only these validators can verify the state of the blockchain. Similarly, in the Proof of Authority (PoA) model, the chain initiator chooses the authority to run the chain. This excludes the majority of participants and creates a situation where only a few people are responsible for ensuring that transactions are correctly verified.

In the Polygon PoS chain, anyone can join the network and start verifying the state of the blockchain. This is important because it allows any participant to become a validator and self-check that all transactions are processed correctly.

The validators on the Polygon PoS Chain must stake their MATIC tokens and run a full node.

MATIC tokens are pledged on the Ethereum main chain. This is also where all validator sets are maintained. If verifiers start to act maliciously, for example, by double signing or severe downtime, their pledge will be cut.

Coin World-Why is Polygon a Commit Chain and not a side chain?

This is also a good time to introduce the two core components of the Polygon PoS chain architecture-Heimdall chain and Bor chain.

Heimdall chain and Bor chain

Heimdall works with the Stake Manager contract deployed on the Ethereum mainnet to coordinate validator selection and update validators.

Since staking is actually done on the Ethereum smart contract, we don’t have to rely on the honesty of the verifier, but instead inherit the security of the Ethereum chain for this key part. Even if most of the validators collude and start to act maliciously, the community can gather and redeploy the contract on Ethereum for a fork, i.e. cut down the malicious validators, and the chain can continue to operate as expected.

Heimdall is also responsible for checkpointing-this will be discussed in detail later in this article.

Bor is the block producer layer of the PoS chain architecture, responsible for aggregating transactions into blocks.

Bor block producers are a subset of validators regularly reorganized by Heimdall validators. Block producers are selected to verify only a certain number of blocks, also known as “span”. After this period of time, the selection process is triggered again.

Let us take a closer look at the process of selecting a block producer.

Coin World-Why is Polygon a Commit Chain and not a side chain?
  1. Suppose there are 3 validators in the pool, they are Alice, Bill and Clara.
  2. Alice pledged 100 MATIC tokens, while Bill and Clara pledged 40 MATIC tokens each.
  3. Verifiers are allocated to slots based on their pledge, because Alice has 100 MATIC tokens pledged, and each slot has 10 tokens (managed and maintained by the verifier), Alice will get a total of 5 slots. Similarly, Bill and Clara got a total of 2 slots.
  4. All validators are assigned to these slots [A, A, A, A, A, B, B, C, C]
  5. Using historical Ethereum blocks as seeds, we shuffle this array.
  6. After shuffling the slots with seeds, we get this array [A, B, A, A, C, B, A, A, C]
  7. Now according to the number of producers (maintained by the verifier governance), we select verifiers from the top. For example, if we want to select 5 producers, we set the producers as [A, B, A, A, C]
  8. Therefore, the producer set for the next span is defined as [A: 3, B:1, C:1 ].
  9. Using this validator set and Tendermint’s proposer selection algorithm, we choose a producer for each sprint on Bor.

This model allows anyone to use any number of MATIC tokens to participate in the protection of the network. It also does not sacrifice transaction speed, because not all validators have to verify blocks all the time.

Let us return to another important function of Heimdall-Checkpointing.

checking point

Checkpoints are important because they provide finality on the Ethereum chain.

The Heimdall layer allows the blocks generated by Bor to be aggregated into a single Merkle root and published to the Ethereum main chain on a regular basis. This published state is also called a checkpoint, so the entire process is called a checkpoint.

The checkpoint proposer was initially selected through Tendermint’s weighted round-robin algorithm. Implement further custom checks based on the success of the checkpoint submission. This allows Polygon PoS Chain to choose to decouple from Tendermint proposers and provide it with functions such as selecting proposers only when the checkpoint transaction on the Ethereum mainnet succeeds or submitting the checkpoint transaction of the previous block when the checkpoint transaction fails.

Submitting checkpoints on Tendermint is a two-stage submission process. The proposer selected by the above algorithm sends a checkpoint with an address in the proposer field, and all other proposers verify it.

Then the next proposer sends a confirmation transaction to prove that the previous checkpoint transaction was successful on the Ethereum mainnet. Each validator set change will be relayed by the validator node on Heimdall embedded on the validator node. This allows Heimdall to always stay in sync with the state of the Polygon contract on the Ethereum main chain.

The Polygon PoS Chain contract deployed on the main chain is considered the ultimate source of truth, so all verification is done by querying the Ethereum main chain contract.

The checkpoint also provides a “certificate of destruction” when withdrawing assets.

Speaking of withdrawal, let’s take a look at another important element of the PoS chain-the two-way Ethereum bridge.

Two-way Ethereum Bridge

A typical two-way bridge relies on a small group of authorities that are usually not even pledged, and are not part of the sidechain verifier set-basically the bridge is usually controlled by several PoA signers. This is an important security issue.

Coin World-Why is Polygon a Commit Chain and not a side chain?

Polygon provides two different ways to move assets between Ethereum and Polygon-Plasma Bridge and PoS Bridge.

Due to the Plasma exit mechanism, Plasma Bridge provides a higher security guarantee. However, due to certain restrictions in the Plasma framework, all withdrawals/withdrawals have a 7-day withdrawal period.

The PoS bridge does not have this limitation, it is protected by a powerful set of validators that we discussed earlier in this article. The state of these validators is maintained on the Ethereum mainnet, and they are guaranteed by all funds in the system-approximately $500 million at the time of writing. As far as we know, the PoS bridge is the only bridge protected by the entire set of validators in the bridge chain; as mentioned earlier, the bridge is usually protected by a small group of PoA signers.

As we have seen, Polygon PoS Chain provides many additional security measures based on the Ethereum main chain, not just a side chain. Perhaps, the commit chain is a better name.

Coin World-Why is Polygon a Commit Chain and not a side chain?

So what do you think of Polygon Commit Chain? Do you think it is valuable to distinguish it from sidechains?

If you like to read this article, you can also check Finematics on Youtube ‌ and Twitter ‌.

Posted by:CoinYuppie,Reprinted with attribution to:https://coinyuppie.com/why-is-polygon-a-commit-chain-and-not-a-side-chain/
Coinyuppie is an open information publishing platform, all information provided is not related to the views and positions of coinyuppie, and does not constitute any investment and financial advice. Users are expected to carefully screen and prevent risks.

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