Parallel Threads: A Flexible Participation Method in the Polkadot Ecosystem

Parachains are an innovative concept within the Polkadot network that allows blockchain projects to participate in Polkadot's security ecosystem in a more flexible manner. This mechanism enables projects that are unable or unwilling to acquire a full parachain slot to still benefit from Polkadot's shared security while paying the corresponding fees for each executed block.

Origin of the Concept

The inspiration for parallel threads comes from the virtual memory technology used in early personal computers. When physical memory is insufficient, the computer can use swap space on the hard drive to extend available memory, allowing more processes to run simultaneously, although some operations may take longer.

Operating Mechanism

On Polkadot's relay chain, some parachain slots will be designated as parallel thread pools. These slots will not attach to fixed parachains, but will serve as a bidding space for parallel threads to compete for inclusion of their candidate blocks through auctioning fees for each block.

The organizer will propose bids priced in DOT to include candidate blocks of parallel threads. Relay chain block producers can select the most profitable candidate blocks from these bids. The tokens obtained from the bids may be distributed in an 80-20 ratio, where 80% goes to the Polkadot treasury and 20% is given to the block producers. This distribution ratio, like many parameters in Polkadot, can be adjusted through the governance mechanism.

Comparison of Parallel Chains and Parallel Threads

From a technical perspective, parachains and parallel threads are very similar. Chains developed using Substrate can present three states during their lifecycle: independent chains (with secure bridging), parachains, or parallel threads. The transition between the latter two states is relatively straightforward, with the main difference being the economic model rather than the technical implementation.

Parallel threads enjoy the same advantages in connecting to Polkadot as complete parachains. They can communicate with other parachains or parallel threads through XCMP and are fully economically secured by the Polkadot validator set.

The main difference lies in the economic model. Parachains need to be registered through governance proposals or slot auctions, while parathreads only require a fixed registration fee, which is significantly lower than the cost of obtaining a parachain slot. The deposit for parathreads will be refunded after their term ends.

It is worth noting that the registration of parallel threads does not guarantee that their blocks will be included in the relay chain. Each time a new block is generated, parallel threads need to participate in a bidding process to compete for inclusion in the verification of the next relay chain block. This mechanism may lead to the formation of a market for inclusion fees similar to that of Bitcoin or Ethereum, where the inclusion price may rise during busy periods.

Economic Model of Parallel Threads

The organizer's compensation comes from two main sources:

1. The transaction fees of the local tokens in the parallel thread itself. If the parallel thread does not have valuable local tokens, DOT can also be used to incentivize organizers.

2. Parachain protocol subsidies. Parachains can mint new tokens to provide additional incentives for organizers. The amount minted may be proportional to the interval time at which the parachain blocks are included in the relay chain.

Although organizers can accept local parallel thread currency payments, transactions can only be conducted using DOT on the relay chain. Therefore, organizers must submit bids for block candidates in DOT.

Parachain Slot Conversion

Projects with parachain slots can choose to convert them into parachreads and vice versa. This provides an elegant exit solution for parachains that have reached their lease period but lack the funds to renew. They can maintain their registered status on the relay chain and only generate new blocks when necessary.

This mechanism helps alleviate the sudden interruptions caused by the expiration of parachain slots, allowing parachains that are no longer economically viable to continue participating in the network in the form of parallel threads, maintaining their functionality.