Elastic Scaling: Streamlining Growth on Polkadot

Elastic scaling is an extremely useful addition for parachains that need higher throughput than allowed by the current Polkadot protocol. This blog from Fatemeh Shirazi explains its importance and how this technical upgrade will come about.

Polkadot’s mission is based on delivering a platform that focuses on excellent scaling and security. The aim is to allow decentralized applications to operate in the best conditions possible.

Polkadot scales by applying a hierarchy to the platform architecture. Parachains are allowed to submit one block for each block on the Relay Chain, the central chain that provides shared security for all parachains. The Relay Chain can serve up to 300 parachains.

The hierarchical architecture of Polkadot allows parachain projects to be able to combine resources and have strong security backing, all but eliminating the threat of attack. If each parachain was to run security on their own blockchains these security resources would be divided, making attacks cheaper and easy to carry out.

Elastic scaling is just one of several exciting changes proposed for Polkadot that open up more opportunities for adoption within the ecosystem.

Scaling a parachain beyond one core

One important aspect of elastic scaling is to allow parachains to produce multiple blocks for each Relay Chain block, and have them validated. These parachain blocks can still be built in a sequential fashion, but the Relay Chain processes them in parallel.

Polkadot can validate many parachain blocks at a time. We refer to the Relay Chain resources and time used to validate a parachain block on the Relay Chain as a “core”, similar to what was previously loosely referred to as a “slot”.

So if the Relay Chain can validate 50 parachain blocks at a time, we say it has 50 cores, just as a processor with 50 cores can execute 50 threads at a time. This way, parachains will be able to obtain more than one core at the same time for execution, so parachains with high throughput will be able to get transactions executed faster.

Core assignment: A new model

The established Polkadot model is that prospective projects apply for slots by participating in an auction. A new project that wins an auction becomes a parachain. The auction determines how many tokens need to be locked. Under the single core model this means a lease period of anything between six months and two years.

Agile Coretime, which is already in the process of being implemented, changes this as it allows for more flexible assignment of cores. “Coretime” refers to the right to use a core on the relay chain. The new changes will permit the purchase of one or more cores for shorter periods of time such as one month, one hour, or even one block, through on-chain purchase or from a secondary market.

Elastic scaling: enabling extra cores

These two changes, multiple cores per parachain plus Agile Coretime, come together to enable elastic scaling. This is a development through which a parachain can lease additional cores on short notice for a short period of time to help them get their blocks validated at a faster rate, and thus execute more transactions. Elastic scaling is useful to various entities in the blockchain space. For example, service providers can serve more of their customers (application developers), which helps them gain increased revenue and reach.

Applications, many of which have unpredictable coretime requirements, will also benefit from elastic scaling.They can save costs by only buying the coretime they need at a specific time, without having to choose between high cost and low performance.

At launch, applications are likely to have a small number of users. Clearly, good ones will build that quantity up over time. Elastic scaling allows them to buy more coretime as they need it, depending on the growth of their users.

It is hard for a project to estimate how much coretime it will require on a future roadmap. If a service provides rigid scaling only, these projects either have to buy significant coretime in bulk at the start - and find the funds to pay for it - or end up with slow services, risking the loss of end users once they become popular.

Cost-effective scaling

What many applications tend to do is acquire more coretime than they need, which raises the price for all parties, and raises the entry bar for application developers. Elastic scaling allows them to only pay for coretime when needed and reduces the price for everyone. Additionally, through the secondary markets that are likely to be introduced with Agile Coretime, projects will be able to resell any coretime they won’t need in future.

Comparison to other scaling models

Until now, Web3 projects that exist as “roll-ups”, typically Layer-2 operations building on Ethereum, have addressed the scalability problem. However, these have flaws of their own, either having to operate with weaker security (as “optimistic” roll-ups) or having to do heavy computation for nodes as per the “zero-knowledge” model.

This comes about because, with roll-ups, the execution of blocks is delegated outside the set of validators. As such, the bulk of the computation and storage is off-chain.

What else can we expect?

CoreJAM, as outlined by Gavin Wood in Dubai last week, is a more far-reaching and general extension of Polkadot’s core model than Agile Coretime or elastic scaling on their own (both, however, would fit neatly into the CoreJAM model).

On top of this, Polkadot can validate more than just chains. Right now, smart contracts on parachains have a limitation in that while calls between contracts on a chain are synchronous and fast, cross-chain calls are slower and asynchronous. This leads to a difficult choice of which chain to be on and therefore which contracts are easy to interoperate with. The CorePlay idea, that is a possible extension of CoreJAM, proposes that the same smart contract can be scheduled with different smart contracts as demand for faster calls allows.

Maximum scalability and security within an interconnected network is how Polkadot plans to encourage a fresh wave of Web3 adoption over the coming months and years - and the technology will be ready to capture the interest.

This article initially appeared in the Polkadot Forum. It has been updated and abridged by Oliver Brett to serve the purposes of the Polkadot blog.