Parallel Threads: Innovative Solutions in the Polkadot Ecosystem

Parachain threads are an innovative concept in the Polkadot network that allows blockchain projects to temporarily participate in Polkadot's security without the need to rent dedicated parachain slots. This mechanism is achieved by economically sharing parachain slots among multiple competing resources. For projects that cannot obtain a full parachain slot or consider acquiring a slot to be economically unreasonable, parachain threads provide a way to participate in Polkadot's shared security, although each executed block requires the payment of corresponding fees. Additionally, it offers an elegant exit solution for projects that no longer require dedicated parachain slots but wish to continue using the relay chain.

The Origin of Parallel Threads

The concept of parallel threads originated from the methods used in personal computers in the late 1980s and early 1990s to manage limited memory resources. At that time, computers faced challenges with physical memory limitations. To address this issue, system developers came up with the idea of using swap space on the hard disk to create virtual memory. This method allowed computers to extend their memory capacity, enabling more processes to run simultaneously, even though some processes might take longer to execute.

The Operating Mechanism of Parallel Threads

On the Polkadot relay chain, some parachain slots will be designated as parachain thread pools. This means that certain parachain slots will not be attached to fixed parachains but will serve as a space for the winners of fee auctions conducted on a block-by-block basis to incorporate their candidate blocks.

The organizer will provide bids in DOT to include parallel thread block candidates. Relay chain block producers can choose to include a block from these bids that contains a parallel thread. Obviously, they would prefer to accept the highest bids to maximize their profits. Tokens from parallel thread bids may be split into two parts, with most going to the Polkadot treasury and a small portion given to the block producers. This allocation ratio, like many other parameters in Polkadot, can be adjusted through governance mechanisms.

Comparison of Parallel Chains and Parallel Threads

From a development perspective, parachains and parallel threads are very similar. Chains developed using Substrate can manifest as independent chains with secure bridging, parachains, or parallel threads at different stages of their lifecycle. The technical threshold for switching between the latter two states is relatively low, as the differences primarily lie in the economic rather than the technical aspect.

Parachains enjoy the same advantages as full parachains when connected to Polkadot. They can exchange messages with other parachains or parathreads via XCMP and are fully economically secured by the set of Polkadot validators.

The main difference between parachains and parathreads lies in their economic models. Parachains need to be registered through the regular Polkadot method, such as governance proposals or parachain slot auctions. In contrast, the registration fee for parathreads is fixed and is usually much lower than the cost of obtaining a parachain slot. Similar to how DOT is returned to the auction winners after being locked during the parachain slot period, the deposit for parathreads will also be refunded after their term ends.

It is worth noting that registering a parallel thread does not guarantee its continued participation. When a parallel thread needs to generate a new block, it must pay fees to participate in the auction for each block in order to compete for inclusion in the validation of the next relay chain block. All registered parallel threads are competing for their blocks to be included.

Economic Model of Parallel Threads

The economic model of parallel threads mainly involves two aspects:

1. Source of the organizer's compensation:

   • If parallel threads have their own local token system, they can pay the organizers from the transaction fees.
   • If there are no local tokens or their value is low, DOT can be used to incentivize organizers.

2. Parallel Thread Protocol Subsidy:

   • Parallel threads can mint new tokens, providing additional incentives for organizers.
   • The number of minted tokens may be time-related; the longer the interval for being included in the relay chain, the more tokens willing to subsidize.
   • This minting process can be achieved through local inflation or similar treasury reserves.

The organizer can accept local parallel thread currency as payment, but bids must be submitted in DOT on the relay chain.

Parachain Slot Conversion

Projects with parallel chain slots can choose to convert them into parallel threads, and vice versa. This provides a graceful exit solution for parallel chains that have reached their rental period and do not have sufficient funds to renew. They can remain registered on the relay chain, but only generate new blocks as needed.

This mechanism helps alleviate the sudden interruptions caused by the expiration of parachain slots, allowing projects to continue functioning within the Polkadot ecosystem even if renting a full parachain slot is no longer economically viable.