One minute to understand the origin of the Polkadot parachain: what problem does it solve?


Achieve scalability for the blockchain and bring flexibility to developers.

Original title: How did the “parachain” scheme come about? 》
Written by: Web3 Foundation Translation: PolkaWorld

This document mainly describes the implementation of the Polkadot Parachain function host , mainly for the implementers of the Polkadot Parachain host. The document is divided into the following sections:

  1. Parachain origin
  2. Agreement overview
  3. Architecture overview
  4. Runtime architecture
  5. Runtime APIs
  6. Node architecture
  7. Data structure and type

This article is the first part of “Parallel Chain Origin” translated by PolkaWorld. Interested students can read the original document for further understanding.

This document aims to describe the purpose, function, and implementation of Polkadot’s parachain function host (software that provides security and advancement for forming parachains). This document is not for specific parachain implementers, but for implementers of Parachain Host. In fact, this document is usually aimed at implementers of Polkadot.

There are other documents that describe this research in more detail. All reference documents are placed in this document and should be read together with this document for a better understanding of the full text. However, this is the only document that aims to describe the key elements of a specific instance of Polkadot and disassemble the research into lower-level technical details and software structure.

Parachain origin

Parachain is a solution to the problem. As with any solution, you cannot understand the problem without first understanding it. So let’s start with the problems faced by blockchain technology, which have led us to explore design spaces like parachains.

Question 1: Scalability

A few years ago, an obvious phenomenon was that the transaction throughput of Bitcoin, Ethereum and other simple proof-of-work (PoW) blockchains was too low.

TODO: What if there are more blockchains?

The Proof of Stake (PoS) system can achieve higher throughput than the PoW blockchain. The PoS system is guaranteed by bound capital, rather than expending effort-the opportunity cost of liquidity VS burning electricity. Their way of working is to choose a group of verifiers with known economic identities, and they lock the tokens in exchange for the right to obtain “verification” or participate in the consensus process. If they are found to perform this process incorrectly, they will be punished by slash, which means that some or all of the locked tokens will be destroyed. This has a strong inhibitory effect on bad behavior.

Since this consensus protocol does not waste resources, block time and agreement can happen faster. The solution to the PoW challenge does not have to be found before the block is created, so the cost of creating a block is reduced to the cost of only creating and distributing the block.

However, to reach consensus on the PoS chain, more than two-thirds of validators must reach full agreement on everything that happens on Layer 1, and all logic is executed as part of the blockchain state machine. This means everyone still needs to check everything. In addition, based on the information received through the asynchronous network, validators may have a different view of the system, which makes it more difficult to reach agreement on the latest state.

Parachain is an example of sharding protocol. Sharding is a concept borrowed from the traditional database architecture. Instead of asking every participant to check every transaction, we ask every participant to check a certain subset of transactions, so that there is enough redundancy so that Byzantine (arbitrarily malicious) participants cannot sneak into invalid transactions. —— At least it is impossible to reverse these transactions without being detected and slashed.

Through the cooperation of sharding and proof of rights and interests, even if not all participants check all state transitions, the parachain host can also provide comprehensive security on many parachains.

TODO: Pay attention to network influence and bridging

Question 2: Flexibility/Specialization

“Not smart” virtual machines cannot provide you with flexibility. Any engineer knows that being able to solve a problem professionally will bring them and their users a multiplier effect.

TODO: Do more with less

After recognizing these problems, we began to look for solutions to these problems, which would allow developers to create and deploy specific purpose blockchains under a unified security source, and have the ability to pass messages between them. This is a heterogeneous sharding solution, which we call a parachain.

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