Parallel Threads: A Flexible Participation Method in the Polkadot Ecosystem

Parallel threads are an innovative concept that allows blockchain projects to participate in the security of the Polkadot network in a more flexible manner. This mechanism enables projects that are unable or unwilling to acquire dedicated parachain slots to temporarily access the shared security system of Polkadot on a block-by-block basis.

Origin of Concepts

The inspiration for parallel threads comes from the virtual memory technology in early personal computers. When physical memory is insufficient, the computer can use hard disk space to create virtual memory, thus expanding the system's memory capacity and allowing more processes to run simultaneously, although it may incur some performance loss.

Operating Mechanism

In the Polkadot network, some parachain slots will be designated as a parachain thread pool. These slots will not be allocated to fixed parachains but will be used to accommodate parachain thread candidate blocks that win through block-level bidding.

The organizer will provide bids priced in DOT to include candidate blocks from parallel threads into the relay chain. Relay chain block producers are incentivized to select the highest bidding candidate blocks to maximize their own profits. These bidding revenues may be distributed in an 80-20 ratio, with 80% going into the network treasury and 20% given to the block producers.

Comparison between Parallel Chains and Parallel Threads

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

Parallel threads enjoy the same core advantages as parallel chains, including the ability to communicate with other chains through XCMP and the complete economic security provided by the Polkadot validator set.

The main difference lies in the economic model: parallel chains need to be registered through governance proposals or slot auctions, while parallel threads only require a lower fixed registration fee. However, parallel threads need to participate in bidding each time they generate a new block in order to compete for inclusion in the next relay chain block.

Economic Model

The economic model of parallel threads mainly involves two aspects:

1. Transaction Fees: Parallel threads can use their own token system or DOT to pay for organizer fees.

2. Protocol Subsidy: Parallel threads can mint new tokens, providing additional incentives for organizers. The minting amount may be proportional to the block interval time.

The organizer can accept local token payments, but must quote in DOT when submitting candidate blocks to the relay chain.

Slot Conversion Mechanism

Parachains can convert their slots into parachreads and vice versa. This provides a flexible option for parachains that are about to expire and unable to renew their lease, allowing them to maintain their registered status on the relay chain and generate new blocks when needed.

This mechanism helps alleviate the sudden interruptions caused by the expiration of parallel chain slots, allowing projects to continue to operate within the Polkadot ecosystem even when renting full slots is no longer economically viable.